View source for Light pollution

{{Short description|Excess artificial light in an environment}}
{{About|light pollution in the visible spectrum|pollution in the radio spectrum|radio spectrum pollution|other uses}}
[[File:Melbourne (AU), Melbourne City Centre -- 2019 -- 1530-4.jpg|thumb|upright=1.3|Light pollution over [[Melbourne]], Australia]]
{{Pollution sidebar|Electromagnetic}}
'''Light pollution''' refers to [[artificial lighting]] that alters the natural patterns of light and dark in ecosystems. In a descriptive sense, light pollution occurs when artificial light is used in a poor or excessive way, especially at night, causing negative effects in our environment and our view of the night sky. Light pollution can be understood not only as a phenomenon resulting from a specific source or kind of pollution, but also as a contributor to the wider, collective impact of various sources of pollution.

Although this type of pollution can exist throughout the day, its effects are magnified during the night with the contrast of the sky's darkness. It has been estimated that 83% of the world's people live under light-polluted skies and that 23% of the world's land area is affected by [[skyglow]].<ref name="NWA" /><ref>{{cite journal |url=https://www.knowablemagazine.org/article/living-world/2018/there-goes-night |first=Stephanie |last=Pain |title=There goes the night |journal=Knowable Magazine |date=March 23, 2018 |publisher=[[Annual Reviews (publisher)|Annual Reviews]] |doi=10.1146/knowable-032218-043601 |doi-access=free |access-date=March 26, 2018 |archive-date=March 11, 2021 |archive-url=https://web.archive.org/web/20210311010733/https://knowablemagazine.org/article/living-world/2018/there-goes-night |url-status=live |url-access=subscription }}</ref>
The area affected by artificial illumination continues to increase.<ref name="Kyba">{{cite journal |last1=Kyba |first1=Christopher C. M. |last2=Kuester |first2=Theres |last3=Sánchez de Miguel |first3=Alejandro |last4=Baugh |first4=Kimberly |last5=Jechow |first5=Andreas |last6=Hölker |first6=Franz |last7=Bennie |first7=Jonathan |last8=Elvidge |first8=Christopher D. |last9=Gaston |first9=Kevin J. |last10=Guanter |first10=Luis |title=Artificially lit surface of Earth at night increasing in radiance and extent |journal=Science Advances |date=November 2017 |volume=3 |issue=11 |article-number=e1701528 |doi=10.1126/sciadv.1701528 |pmid=29181445 |pmc=5699900 |bibcode=2017SciA....3E1528K }}</ref> A major side effect of [[urbanization]], light pollution is blamed for compromising health, disrupting ecosystems, and spoiling aesthetic environments. Studies show that urban areas are more at risk.<ref name="Han-2014">{{Cite journal |last1=Han |first1=Pengpeng |last2=Huang |first2=Jinliang |last3=Li |first3=Rendong |last4=Wang |first4=Lihui |last5=Hu |first5=Yanxia |last6=Wang |first6=Jiuling |last7=Huang |first7=Wei |date=16 June 2014 |title=Monitoring Trends in Light Pollution in China Based on Nighttime Satellite Imagery |journal=Remote Sensing |language=en |volume=6 |issue=6 |pages=5541–5558 |doi=10.3390/rs6065541 |doi-access=free |bibcode=2014RemS....6.5541H |issn=2072-4292}}</ref> Globally, it has increased by at least 49% from 1992 to 2017.<ref>{{Cite journal |last1=Sánchez de Miguel |first1=Alejandro |last2=Bennie |first2=Jonathan |last3=Rosenfeld |first3=Emma |last4=Dzurjak |first4=Simon |last5=Gaston |first5=Kevin J. |date=January 2021 |title=First Estimation of Global Trends in Nocturnal Power Emissions Reveals Acceleration of Light Pollution |journal=Remote Sensing |language=en |volume=13 |issue=16 |page=3311 |doi=10.3390/rs13163311 |bibcode=2021RemS...13.3311S |issn=2072-4292|doi-access=free |hdl=10261/255323 |hdl-access=free }}</ref>

Light pollution is caused by inefficient or unnecessary use of artificial light. Specific categories of light pollution include light trespass, over-illumination, glare, light clutter, and skyglow. A single offending light source often falls into more than one of these categories.<ref name="Kaushik-2022" /><ref name="Chepesiuk-2009" />

Solutions to light pollution are often steps like adjusting [[light fixture]]s or using more appropriate [[Electric light|light bulbs]]. Further remediation can be done with more efforts to educate the public in order to push legislative change.<ref>{{Cite journal |last1=Zielińska-Dabkowska |first1=Karolina M. |last2=Xavia |first2=Kyra |last3=Bobkowska |first3=Katarzyna |date=2020 |title=Assessment of Citizens' Actions against Light Pollution with Guidelines for Future Initiatives |journal=Sustainability |language=en |volume=12 |issue=12 |page=4997 |doi= 10.3390/su12124997|doi-access=free |bibcode=2020Sust...12.4997Z |issn= }}</ref> However, because it is a man-made phenomenon, addressing its impacts on humans and the environment has political, social, and economic considerations.

==Definitions==

Light [[pollution]] is the presence of  artificial light in otherwise dark conditions.<ref>{{Cite journal
| last1 = Verheijen | first1 = F. J.
| title = Photopollution: Artificial light optic spatial control systems fail to cope with. Incidents, causation, remedies
| journal = Experimental Biology
| volume = 44
| issue = 1
| pages = 1–18
| year = 1985
| pmid = 3896840
}}</ref><ref>{{cite journal|doi=10.1046/j.1365-8711.2000.03562.x|date=2000|last1=Cinzano|pages=641–657|volume=318|journal=[[Monthly Notices of the Royal Astronomical Society]]|url=http://www.lightpollution.it/cinzano/download/mnras_paper.pdf|first1=P.|last2=Falchi|first2=F.|last3=Elvidge|first3=C. D.|last4=Baugh|first4=K. E.|title=The artificial night sky brightness mapped from DMSP Operational Linescan System measurements|issue=3|doi-access=free |arxiv=astro-ph/0003412|bibcode=2000MNRAS.318..641C|s2cid=15679234|access-date=2010-03-31|archive-date=2021-03-11|archive-url=https://web.archive.org/web/20210311010238/http://www.lightpollution.it/cinzano/download/mnras_paper.pdf|url-status=live}}</ref><ref>[http://amper.ped.muni.cz/light/lp_what_is.pdf Hollan, J: What is light pollution, and how do we quantify it?] {{Webarchive|url=https://web.archive.org/web/20110718180717/http://amper.ped.muni.cz/light/lp_what_is.pdf |date=2011-07-18 }}. Darksky2008 conference paper, Vienna, August 2008. Updated April 2009.</ref><ref>Marín, C. and Orlando, G. (eds.) (June 2009) [http://www.starlight2007.net/pdf/FinalReportFuerteventuraSL.pdf Starlight Reserves and World Heritage] {{Webarchive|url=https://web.archive.org/web/20200927091205/https://www.starlight2007.net/pdf/FinalReportFuerteventuraSL.pdf |date=2020-09-27 }}. Starlight Initiative, IAC and the UNESCO World Heritage Centre. Fuerteventura, Spain.</ref>

The term is most commonly used in relation to in the outdoor environment and surrounding, but is also used to refer to artificial light indoors. Adverse consequences are multiple; some of them may not be known yet. Light pollution makes it harder for people in cities that use excessive artificial light hard, and like other pollutants it can harm our environment. Light pollution is a side-effect of [[industrial civilization]]. Its sources include building exterior and interior lighting, advertising, outdoor area lighting (such as car parks), offices, factories, streetlights, and illuminated sporting venues. It is most severe in highly industrialized, densely populated areas of North America, Europe, and Asia and in major cities in the Middle East and North Africa like [[Tehran]] and [[Cairo]], but even relatively small amounts of light can be noticed and create problems. Awareness of the harmful effects of light pollution began in the second half of the 19th century,<ref>{{cite book|last1=Guillemain|first1=Amédée|title=Le Ciel, notions d'astronomie à l'usage des gens du monde et de la jeunesse|date=1864|publisher=Librairie de L. Hachette et Cie|location=Paris|pages=101, 383|url=https://gallica.bnf.fr/ark:/12148/bpt6k62098808/f13.item.r|access-date=2021-02-07|archive-date=2021-03-11|archive-url=https://web.archive.org/web/20210311005601/https://gallica.bnf.fr/ark:/12148/bpt6k62098808/f13.item.r|url-status=live}}</ref> but efforts to address its effects did not begin until the 1950s.<ref>{{cite journal|last1=Portree|first1=David. S. F.|title=Flagstaff's Battle for Dark Skies|journal=The Griffith Observer|date=2002|issue=October, 2002}}</ref> In the 1980s a global [[dark-sky movement]] emerged with the founding of the [[International Dark-Sky Association]] (IDA). There are now such educational and advocacy organizations in many countries worldwide.

About 83% of people, including 99% of Europeans and Americans, live under light-polluted skies that are more than 10% brighter than natural darkness.  80% of North Americans cannot see the [[Milky Way]] galaxy.<ref>{{Cite web |last=Yong |first=Ed |date=2022-06-13 |title=How Animals Perceive the World |url=https://www.theatlantic.com/magazine/archive/2022/07/light-noise-pollution-animal-sensory-impact/638446/ |access-date=2022-06-14 |website=The Atlantic |language=en |archive-date=2023-06-03 |archive-url=https://web.archive.org/web/20230603170150/https://www.theatlantic.com/magazine/archive/2022/07/light-noise-pollution-animal-sensory-impact/638446/ |url-status=live }}</ref>

==Types==

[[File:Skybeamer-uniqema-640.jpg|thumb|upright|A light pollution source, using a broad spectrum [[metal halide lamp]], pointing upward at Uniqema factory, [[Gouda, South Holland|Gouda]], the Netherlands]]

===Light trespass===

Light trespass occurs when unwanted light enters one's property, an example for this would be when : A neighbor installs a new light fixture on their property. It’s unshielded and casts a bright light that spills onto your property and perhaps even inside your home.<ref name="International Dark-Sky Association">Liebel, Brian. “My Neighbor’s Lighting.” ''DarkSky International'', 26 May 2015, updated 22 Aug. 2023, <nowiki>https://darksky.org/resources/what-is-light-pollution/light-pollution-solutions/lighting/my-neighbors-lighting/</nowiki>.</ref> A common light trespass problem occurs when a strong light enters the window of one's home from the outside, causing problems such as [[sleep deprivation]]. A number of cities in the U.S. have developed standards for outdoor lighting to protect the rights of their citizens against light trespass.

The [[International Dark-Sky Association|Dark-Sky Association]] was started to reduce the light going up into the sky which reduces the visibility of stars (see Skyglow below). This is any light that is emitted more than 90° above [[nadir]]. By limiting light at this 90° mark they have also reduced the light output in the 80–90° range which creates most of the light trespass issues.
[[File:Phoenix Lights from afar.jpg|thumb|The city of Phoenix, seen from {{convert|55|mi}} away in [[Surprise, Arizona]]]]

U.S. federal agencies may also enforce standards and process complaints within their areas of jurisdiction. For instance, in the case of light trespass by white [[strobe]] lighting from communication towers in excess of [[Federal Aviation Administration|FAA]] minimum lighting requirements<ref>{{cite web| title = AC 70/7460-1K Obstruction Marking and Lighting| date = 2007-02-01| url = http://wireless.fcc.gov/antenna/documentation/faadocs/7460-1K.pdf| access-date = 2009-07-04| archive-url = https://web.archive.org/web/20100527213109/http://wireless.fcc.gov/antenna/documentation/faadocs/7460-1K.pdf| archive-date = 2010-05-27}}</ref> the [[Federal Communications Commission]] maintains an Antenna Structure Registration database<ref name="FCC Antenna Structure Registration">{{cite web|title = FCC Antenna Structure Registration|url = http://wireless.fcc.gov/antenna/index.htm?&job=home|access-date = 2009-07-04|archive-url = https://web.archive.org/web/20090207035625/http://wireless.fcc.gov/antenna/index.htm?&job=home|archive-date = 2009-02-07}}</ref> information which citizens may use to identify offending structures and provides a mechanism for processing citizen inquiries and complaints.<ref name="fcc.gov">{{cite web|title = FCC Consumer & Governmental Affairs Bureau|url = http://www.fcc.gov/cgb/cgb_offices.html#CICD|publisher = U.S. Federal Communications Commission|date = March 2011|access-date = 2006-12-03|archive-date = 2010-08-10|archive-url = https://web.archive.org/web/20100810191544/http://www.fcc.gov/cgb/cgb_offices.html#CICD|url-status = live}}</ref> The [[U.S. Green Building Council]] (USGBC) has also incorporated a credit for reducing the amount of light trespass and sky glow into their environmentally friendly building standard known as [[Leadership in Energy and Environmental Design|LEED]].

Light trespass can be reduced by selecting light fixtures that limit the amount of light emitted more than 80° above the [[nadir]]. The [[Illuminating Engineering Society of North America|IESNA]] definitions include full cutoff (0%), cutoff (10%), and semi-cutoff (20%). (These definitions also include limits on light emitted above 90° to reduce sky glow.)

===Over-illumination===

[[File:HPS-lamps.jpg|thumb|An office building is illuminated by [[sodium lamp|high-pressure sodium (HPS)]] lamps shining upward. Much light goes into the sky and neighboring apartment blocks, causing light pollution.]]Over-illumination is the excessive and unnecessary use of light.<ref name="Chepesiuk-2009">{{Cite journal |last=Chepesiuk |first=Ron |date=1 January 2009 |title=Missing the Dark: Health Effects of Light Pollution |journal=Environmental Health Perspectives |language=en |volume=117 |issue=1 |pages=A20-7 |doi=10.1289/ehp.117-a20 |issn=0091-6765 |pmc=2627884 |pmid=19165374}}</ref>

A large and overabundant amount of electricity is required to support light consumption in the United States. U.S homes consumed 81 billion kilowatt hours (kWh) of electricity for lighting in 2020 according to the U.S. Energy Information Administration (EIA).<ref name="www.eia.gov">{{Cite web |title=Frequently Asked Questions (FAQs) - U.S. Energy Information Administration (EIA) |url=https://www.eia.gov/tools/faqs/faq.php?id=99&t=3#:~:text=According%20to%20the%20most%20recent%20CBECS%2C%20in%202018%2C%20electricity%20consumption,consumption%20by%20U.S.%20commercial%20buildings. |access-date=29 March 2024 |website=www.eia.gov |archive-date=29 March 2024 |archive-url=https://web.archive.org/web/20240329024520/https://www.eia.gov/tools/faqs/faq.php?id=99&t=3#:~:text=According%20to%20the%20most%20recent%20CBECS%2C%20in%202018%2C%20electricity%20consumption,consumption%20by%20U.S.%20commercial%20buildings. |url-status=live }}</ref> Additionally, the EIA reported that 208 billion kWh and 53 billion kWh of electricity were used for commercial and manufacturing buildings respectively in 2018.<ref name="www.eia.gov" />

Light use is not excessive in all developed countries. Amongst developed countries there are large variations in patterns of light use. American cities emit three to five times more light to space per capita compared to German cities.<ref>{{cite journal |last1=Kyba |first1=Christopher |last2=Garz |first2=Stefanie |last3=Kuechly |first3=Helga |last4=de Miguel |first4=Alejandro |last5=Zamorano |first5=Jaime |last6=Fischer |first6=Jürgen |last7=Hölker |first7=Franz |date=23 December 2014 |title=High-Resolution Imagery of Earth at Night: New Sources, Opportunities and Challenges |journal=Remote Sensing |volume=7 |issue=1 |pages=1–23 |bibcode=2014RemS....7....1K |doi=10.3390/rs70100001 |doi-access=free}}<!--|access-date=8 March 2015--></ref>

Over-illumination stems from several factors:

* Consensus-based standards or norms that are not based on [[vision science]];<ref>{{cite journal |last1=Fotios |first1=S |last2=Gibbons |first2=R |date=9 January 2018 |title=Road lighting research for drivers and pedestrians: The basis of luminance and illuminance recommendations |journal=Lighting Research & Technology |volume=50 |issue=1 |pages=154–186 |doi=10.1177/1477153517739055 |doi-access=free}}</ref>
* Improper design, by specifying higher levels of light than needed for a given visual task;<ref name="EcoSky2">{{cite journal |last1=Kyba |first1=Christopher C. M. |last2=Mohar |first2=Andrej |last3=Pintar |first3=Gašper |last4=Stare |first4=Jurij |date=20 February 2018 |title=Reducing the environmental footprint of church lighting: matching façade shape and lowering luminance with the EcoSky LED |journal=International Journal of Sustainable Lighting |volume=19 |issue=2 |page=132 |doi=10.26607/ijsl.v19i2.80 |doi-access=free}}</ref>
* Incorrect choice of fixtures or [[light bulbs]], which do not direct light into areas as needed;<ref name="EcoSky2" />
* Improper selection of hardware to utilize more energy than needed to accomplish the lighting task;
* Incomplete training of building managers and occupants to use lighting systems efficiently;
* Inadequate lighting maintenance resulting in increased [[stray light]] and energy costs;
* "Daylight lighting" demanded by citizens to reduce crime or by shop owners to attract customers;<ref name="ReferenceB2">Over-illumination can be a design choice, not a fault. In both cases target achievement is questionable.</ref>
* Substitution of old lamps with more efficient [[LED]]s using the same electrical power; and
* Indirect lighting techniques, such as illuminating a vertical wall to bounce light onto the ground.
* Institutions who illuminate their buildings not to improve navigation, but "to show that its empire is inescapable".<ref name="The New Yorker-2023">{{Cite magazine |date=2023-02-20 |title=Is Artificial Light Poisoning the Planet? |url=https://www.newyorker.com/magazine/2023/02/27/darkness-manifesto-book-johan-eklof |access-date=2023-02-21 |magazine=The New Yorker |language=en-US |archive-date=2023-02-21 |archive-url=https://web.archive.org/web/20230221001754/https://www.newyorker.com/magazine/2023/02/27/darkness-manifesto-book-johan-eklof |url-status=live }}</ref>
* Lighting less for the benefit of seeing at night, and more for institutions to push working hours beyond natural [[daylight]] hours. An economic and financial gain as opposed to a necessity.<ref name="The New Yorker-2023" />

Most of these issues can be readily corrected with available, inexpensive [[technology]],<ref>{{Cite arXiv |last1=Raki |first1=Gholamreza Fardipour |last2=Khakzad |first2=Mohsen |date=2024 |title=Silicon-Photomultiplier (SiPM) Protection Against Over-Current and Over-Illumination |class=hep-ex |eprint=2404.07875}}</ref> and with the resolution of landlord/tenant practices that create barriers to rapid correction of these matters. Most importantly, public awareness would need to improve for industrialized countries to realize the large payoff in reducing over-illumination.<ref>{{Cite journal |last1=Kim |first1=Kyung Hee |last2=Choi |first2=Jae Wook |last3=Lee |first3=Eunil |last4=Cho |first4=Yong Min |last5=Ahn |first5=Hyung Rae |date=2015 |title=A study on the risk perception of light pollution and the process of social amplification of risk in Korea |url=http://link.springer.com/10.1007/s11356-015-4107-5 |journal=Environmental Science and Pollution Research |language=en |volume=22 |issue=10 |pages=7612–7621 |doi=10.1007/s11356-015-4107-5 |pmid=25649389 |bibcode=2015ESPR...22.7612K |issn=0944-1344|url-access=subscription }}</ref>

In certain cases, an over-illumination lighting technique may be needed. For example, indirect lighting is often used to obtain a "softer" look, since hard direct lighting is generally found less desirable for certain surfaces, such as skin. The indirect lighting method is perceived as cozier and suits bars, restaurants, and living quarters. It is also possible to block the direct lighting effect by adding softening filters or other solutions, though intensity will be reduced.<ref>{{Cite arXiv |last1=Miguel |first1=De |last2=Sánchez |first2=Alejandro |date=2022-09-05 |title=Pros and cons of gaussian filters versus step filters for light pollution monitoring |class=astro-ph.IM |language=en |eprint=2209.02100}}</ref>

===Glare===

<!-- This section is linked from [[Solar power]]. -->
{{Main|Glare (vision)}}

Glare can be categorized into different types. One such classification is described in a book by Bob Mizon, coordinator for the [[British Astronomical Association]]'s [[Commission for Dark Skies|Campaign for Dark Skies]], as follows:<ref>Mizon, Bob (2001) ''Light Pollution: Responses and Remedies''. Springer. {{ISBN|1-85233-497-5}}</ref>
* ''Blinding glare'' describes effects such as that caused by staring into the Sun. It is completely blinding and leaves temporary or permanent vision deficiencies.
* ''Disability glare'' describes effects such as being blinded by oncoming car lights, or light scattering in fog or in the eye, reducing contrast, as well as reflections from print and other dark areas that render them bright, with a significant reduction in sight capabilities.
* ''Discomfort glare'' does not typically cause a dangerous situation in itself, though it is annoying and irritating at best. It can potentially cause fatigue if experienced over extended periods.

According to Mario Motta, president of the [[Massachusetts Medical Society]], "...{{nbsp}}glare from bad lighting is a [[Public health|public-health]] hazard—especially the older you become. Glare light scattering in the eye causes loss of contrast and leads to unsafe driving conditions, much like the glare on a dirty windshield from low-angle sunlight or the high beams from an oncoming car."<ref name="Motta-2009">{{cite web| last = Motta| first = Mario| title = U.S. Physicians Join Light-Pollution Fight| work = news| publisher = Sky & Telescope| date = 2009-06-22| url = http://www.skyandtelescope.com/news/48814012.html| access-date = 2009-06-23| archive-url = https://web.archive.org/web/20090624203356/http://www.skyandtelescope.com/news/48814012.html| archive-date = 2009-06-24}}</ref> In essence bright and/or badly shielded lights around roads can partially blind drivers or pedestrians and contribute to accidents.

The blinding effect is caused in large part by reduced contrast due to light scattering in the eye by excessive brightness, or to the reflection of light from dark areas in the field of vision, with luminance similar to the background luminance. This kind of glare is a particular instance of disability glare, called veiling glare. (This is not the same as loss of accommodation of [[night vision]] which is caused by the direct effect of the light itself on the eye.)

===Light clutter===

[[File:Las Vegas Strip.png|thumb|The [[Las Vegas Strip]] displays excessive groupings of colorful lights. This is a classic example of light clutter.]][[File:San Tan Mountain Lights.jpg|thumb|View of the Phoenix metro area from the top of Goldmine Trail in the San Tan Mountains]]

Light clutter refers to excessive groupings of lights. Groupings of lights may generate confusion, distract from obstacles (including those that they may be intended to illuminate), and potentially cause accidents. Clutter is particularly noticeable on roads where the [[street light]]s are badly designed, or where brightly lit advertisements surround the roadways. Depending on the motives of the person or organization that installed the lights, their placement and design can even be intended to distract drivers, and can contribute to accidents.<ref name="Kaushik-2022">{{Cite journal |last1=Kaushik |first1=Komal |last2=Nair |first2=Soumya |last3=Ahamad |first3=Arif |date=September 2022 |title=Studying light pollution as an emerging environmental concern in India |journal=Journal of Urban Management |volume=11 |issue=3 |pages=392–405 |doi=10.1016/j.jum.2022.05.012 |issn=2226-5856|hdl=10419/271475 |hdl-access=free }}</ref>

=== Sky glow ===
[[Skyglow|Sky glow]] is the bright haze above cities that is produced from excessive artificial lighting at night.<ref name="Chepesiuk-2009" /> This type of light pollution is created from artificial light reflecting in the sky and bouncing around the different types of particles that reside in the atmosphere<ref>{{Cite journal |last1=Kaushik |first1=Komal |last2=Nair |first2=Soumya |last3=Ahamad |first3=Arif |date=September 2022 |title=Studying light pollution as an emerging environmental concern in India |journal=Journal of Urban Management |volume=11 |issue=3 |pages=392–405 |doi=10.1016/j.jum.2022.05.012 |issn=2226-5856 |hdl-access=free |hdl=10419/271475}}</ref> The effect of sky glow can be harmful in [[astronomy]] and on the health of many organisms. It worsens the visibility of the stars, the [[Milky Way]], and significantly increases the natural light levels at night.<ref>{{Cite journal |last1=Kyba |first1=Christopher C. M. |last2=Tong |first2=Kai Pong |last3=Bennie |first3=Jonathan |last4=Birriel |first4=Ignacio |last5=Birriel |first5=Jennifer J. |last6=Cool |first6=Andrew |last7=Danielsen |first7=Arne |last8=Davies |first8=Thomas W. |last9=Outer |first9=Peter N. den |last10=Edwards |first10=William |last11=Ehlert |first11=Rainer |last12=Falchi |first12=Fabio |last13=Fischer |first13=Jürgen |last14=Giacomelli |first14=Andrea |last15=Giubbilini |first15=Francesco |date=2015-02-12 |title=Worldwide variations in artificial skyglow |journal=Scientific Reports |language=en |volume=5 |issue=1 |page=8409 |doi=10.1038/srep08409 |pmid=25673335 |pmc=5389131 |bibcode=2015NatSR...5.8409K |issn=2045-2322}}</ref>

===From satellites===
{{main|Satellite flare}}

[[File:Night sky at ESO's Paranal Observatory around twilight, Eso2004a.jpg|thumb|upright|Visibility of satellites during twilight marked green and red. 30° above the horizon is where most astronomical observations take place. In Earth's shadow, represented by the darker area on the left, satellites become practically invisible.]]
Also contributing to light pollution are [[artificial satellites]]. With increasing numbers of [[satellite constellation]]s such as [[OneWeb#Concerns|OneWeb]], [[Starlink]], and [[Project Kuiper|Kuiper]], members of the astronomical community, notably the [[International Astronomical Union|IAU]], fear that light pollution will increase significantly, one of many concerns reported in the media regarding satellite overcrowding.<ref name="iau">{{cite web |title=IAU's statement on satellite constellations |url=https://www.iau.org/news/announcements/detail/ann19035/ |website=International Astronomical Union |access-date=3 June 2019 |archive-date=27 May 2020 |archive-url=https://web.archive.org/web/20200527073625/https://www.iau.org/news/announcements/detail/ann19035/ |url-status=live }}</ref><ref>{{cite web|url=http://www.astronomy.com/news/2019/06/light-pollution-from-satellites-will-get-worse-but-how-much|title=Light pollution from satellites will get worse. But how much?|date=2019-06-14|access-date=2019-11-07|website=astronomy.com|archive-date=2021-04-28|archive-url=https://web.archive.org/web/20210428172415/https://astronomy.com/news/2019/06/light-pollution-from-satellites-will-get-worse-but-how-much|url-status=live}}</ref><ref>{{cite web|url=https://www.theverge.com/2019/5/29/18642577/spacex-starlink-satellite-constellation-astronomy-light-pollution|date=2019-05-29|title=SpaceX Starlink satellite constellation astronomy light pollution|archive-date=2020-11-29|archive-url=https://web.archive.org/web/20201129020343/https://www.theverge.com/2019/5/29/18642577/spacex-starlink-satellite-constellation-astronomy-light-pollution}}</ref> Public discourse surrounding the continuing deployment of satellite constellations includes multiple petitions by astronomers and citizen scientists,<ref>{{cite web|url=https://astronomersappeal.wordpress.com/|title=Appeal by Astronomers|first=Stefano|last=Gallozzi|date=2020-01-09|archive-url=https://web.archive.org/web/20201129001704/https://astronomersappeal.wordpress.com/2020/01/09/astronomers-appeal/|archive-date=2020-11-29}}</ref><ref>{{cite web|url=https://www.astro.princeton.edu/~gbakos/satellites/index.html|title=Light pollution from Satellites|archive-url=https://web.archive.org/web/20201129023557/https://www.astro.princeton.edu/~gbakos/satellites/index.html|archive-date=2020-11-29|first=Gaspar|last=Bakos}}</ref> and has raised questions about which regulatory bodies hold jurisdiction over human actions that obscure starlight.<ref>{{cite web|title=SpaceX's Starlink satellites are about to ruin stargazing for everyone|url=https://theconversation.com/spacexs-starlink-satellites-are-about-to-ruin-stargazing-for-everyone-149516|date=2020-11-17|first=Samantha|last=Lawler|editor-first1=Nehal |editor-last1=El-Hadi |doi=10.64628/AAM.unhydkawg |archive-url=https://web.archive.org/web/20201129000433/https://theconversation.com/spacexs-starlink-satellites-are-about-to-ruin-stargazing-for-everyone-149516|archive-date=2020-11-29}}</ref><ref>{{cite web|url=https://www.rcinet.ca/en/2020/11/18/astronomers-vs-tech-giants-in-space/|title=Astronomers vs tech giants in space|first=Marc|last=Montgomery|date=2020-11-18|archive-url=https://web.archive.org/web/20201129000829/https://www.rcinet.ca/en/2020/11/18/astronomers-vs-tech-giants-in-space/|archive-date=2020-11-29}}</ref><ref>{{cite press release|url=https://www.darksky.org/why-do-mega-constellations-matter-to-the-dark-sky-community/|title=Why do mega constellations matter to the Dark Sky community|date=2019-12-27|archive-url=https://web.archive.org/web/20201117232230/https://www.darksky.org/why-do-mega-constellations-matter-to-the-dark-sky-community/#webpage|archive-date=2020-11-17}}</ref><ref>{{cite web |url=https://aas.org/satellite-constellations-1-workshop-report|title=Satellite Constellations 1 Workshop Report |website=American Astronomical Society |date=2020-08-25|archive-url=https://web.archive.org/web/20201129021515/https://aas.org/satellite-constellations-1-workshop-report|archive-date=2020-11-29}}</ref><ref>{{cite press release|url=https://noirlab.edu/public/announcements/ann20011/|date=2020-08-21|title=Media advisory: Press Conference to Unveil Conclusions from Satellite Constellations 1 (SATCON1) Workshop|archive-url=https://web.archive.org/web/20201129021144/https://noirlab.edu/public/announcements/ann20011/|archive-date=2020-11-29}}</ref><ref>{{cite arXiv|eprint=2001.10952|title=Concerns about ground based astronomical observations: A step to Safeguard the Astronomical Sky|first1=Stefano|last1=Gallozzi|first2=Marco|last2=Scardia|first3=Michele|last3=Maris|date=2020-02-04|class=astro-ph.IM}}</ref>

==Measurement==

=== Issues to measuring light pollution ===
Measuring the effect of sky glow on a global scale is a complex procedure.<ref>{{Cite journal |last1=Matsumoto |first1=T. |last2=Tsumura |first2=K. |last3=Matsuoka |first3=Y. |last4=Pyo |first4=J. |date=2018-08-09 |title=Zodiacal Light Beyond Earth Orbit Observed with Pioneer 10 |journal=The Astronomical Journal |volume=156 |issue=3 |page=86 |doi=10.3847/1538-3881/aad0f0 |doi-access=free |arxiv=1808.03759 |bibcode=2018AJ....156...86M |issn=0004-6256}}</ref> The natural atmosphere is not completely dark, even in the absence of terrestrial sources of light and illumination from the Moon. This is caused by two main sources: ''airglow'' and ''scattered light''.

At high altitudes, primarily above the [[mesosphere]], there is enough UV radiation from the sun at very short wavelengths to cause [[ionization]]. When the ions collide with electrically neutral particles they recombine and emit photons in the process, causing [[airglow]]. The degree of ionization is sufficiently large to allow a constant emission of radiation even during the night when the upper atmosphere is in the Earth's shadow. Lower in the atmosphere all the solar photons with energies above the ionization potential of N<sub>2</sub> and O<sub>2</sub> have already been absorbed by the higher layers and thus no appreciable ionization occurs.

Apart from emitting light, the sky also scatters incoming light, primarily from distant stars and the [[Milky Way]], but also the [[zodiacal light]], sunlight that is reflected and backscattered from interplanetary dust particles.<ref>{{Cite journal |last1=Carleton |first1=Timothy |last2=Windhorst |first2=Rogier A. |last3=O'Brien |first3=Rosalia |last4=Cohen |first4=Seth H. |last5=Carter |first5=Delondrae |last6=Jansen |first6=Rolf |last7=Tompkins |first7=Scott |last8=Arendt |first8=Richard G. |last9=Caddy |first9=Sarah |last10=Grogin |first10=Norman |last11=Kenyon |first11=Scott J. |last12=Koekemoer |first12=Anton |last13=MacKenty |first13=John |last14=Casertano |first14=Stefano |last15=Davies |first15=Luke J. M. |date=2022-10-04 |title=SKYSURF: Constraints on Zodiacal Light and Extragalactic Background Light through Panchromatic HST All-sky Surface-brightness Measurements: II. First Limits on Diffuse Light at 1.25, 1.4, and 1.6 μm |journal=The Astronomical Journal |volume=164 |issue=5 |page=170 |doi=10.3847/1538-3881/ac8d02 |doi-access=free |arxiv=2205.06347 |bibcode=2022AJ....164..170C |issn=0004-6256}}</ref>

The amount of airglow and zodiacal light is quite varied (depending, amongst other things on sunspot activity and the [[Solar cycle]]) but given optimal conditions, the darkest possible sky has a brightness of about 22 magnitude/square arcsecond. If a full moon is present, the [[sky brightness]] increases to about 18 magnitude/sq. arcsecond depending on local atmospheric transparency, 40 times brighter than the darkest sky. In densely populated areas a sky brightness of 17 magnitude/sq. arcsecond is not uncommon, or as much as 100 times brighter than is natural.

=== Satellite imagery measuring ===
To precisely measure how bright the sky gets, night time satellite imagery of the earth is used as raw input for the number and intensity of light sources. These are put into a physical model<ref name="Cinzano-2001">{{cite journal
 |url         = http://debora.pd.astro.it/cinzano/download/0108052.pdf
 |title       = The first world atlas of the artificial night sky brightness
 |journal     = Mon. Not. R. Astron. Soc.
 |volume      = 328
 |date        = 2001
 |pages       = 689–707
 |doi         = 10.1046/j.1365-8711.2001.04882.x
 |issue       = 3
 |arxiv       = astro-ph/0108052
 |bibcode     = 2001MNRAS.328..689C
 |archive-url  = https://web.archive.org/web/20060819051651/http://debora.pd.astro.it/cinzano/download/0108052.pdf
 |archive-date = 2006-08-19
|last1        = Cinzano
 |first1      = P.
 |last2       = Falchi
 |first2      = F.
 |last3       = Elvidge
 |first3      = C. D.
 |last4       = Baugh
 |first4      = K. E.
 |doi-access = free
 |s2cid = 15365532
 }}</ref> of scattering due to air molecules and aerosoles to calculate cumulative sky brightness. Maps that show the enhanced sky brightness have been prepared for the entire world.<ref>{{in lang|it}} [http://www.lightpollution.it/worldatlas/pages/fig1.htm The World Atlas of the Artificial Night Sky Brightness] {{Webarchive|url=https://web.archive.org/web/20100923212042/http://www.lightpollution.it/worldatlas/pages/fig1.htm |date=2010-09-23 }}. Lightpollution.it. Retrieved 2011-12-03.</ref>

=== Ground-based monitoring ===
In addition to satellite-based observations, ground-based networks of photometers have become essential for monitoring light pollution over time. One of the most widely used instruments is the [[Sky Quality Meter]] (SQM), a compact device that measures night sky brightness (NSB) in magnitudes per square arcsecond. SQMs are deployed by both professional observatories and citizen scientists worldwide, providing high temporal resolution data that complements remote sensing approaches.

Long-term SQM datasets from urban, intermediate, and rural sites have revealed measurable increases in light pollution. A 2023 study analyzing over a decade of data from 26 sites across Europe - including cities such as Stockholm, Berlin, and Vienna - found average annual increases in NSB of 1.7% in rural areas, 1.8% in urban areas, and 3.7% in intermediate areas. These trends were corrected for sensor aging using twilight calibration methods and adjusted for atmospheric factors such as albedo, vegetation cover, and aerosols through an empirical regression model.<ref>Puschnig, J., Wallner, S., Schwope, A., Näslund, M. (2023). Long-term trends of light pollution assessed from SQM measurements and an empirical atmospheric model. ''Monthly Notices of the Royal Astronomical Society'', 518(3), 4449–4465. https://doi.org/10.1093/mnras/stac3003</ref>

Ground-based studies have also shown that high levels of artificial light at night can suppress the natural circalunar pattern in sky brightness. In urban areas where the NSB exceeds 16.5 mag/arcsec², the variation associated with the moon cycle becomes nearly undetectable, potentially affecting species that rely on moonlight for behavior or navigation.<ref>Puschnig, J., Wallner, S., & Posch, T. (2020). Circalunar variations of the night sky brightness – an FFT perspective on the impact of light pollution. ''MNRAS'', 492(2), 2622–2637. https://doi.org/10.1093/mnras/stz3514</ref>

National SQM networks have been established in several countries. In Austria, the provincial government of Upper Austria operates a dense SQM network to support both astronomical and environmental research.<ref>{{Cite journal | last1 = Posch
 | first1 = T. | last2 = Binder | first2 = F. | last3 = Puschnig | first3 = J. | title = Quantitative assessment of light pollution in Upper Austria | journal = Journal of Quantitative Spectroscopy and Radiative Transfer | volume = 211
 | pages = 144–153 | date = 2018 | doi = 10.1016/j.jqsrt.2018.03.010 | arxiv = 1803.09811 }}</ref> In Spain, coordinated efforts by researchers including Bará and colleagues have helped quantify the relative contributions of streetlights, traffic, and residential lighting to NSB.<ref>{{Cite journal | last1 = Bará | first1 = S.
 | last2 = Lima | first2 = R. C. | last3 = Zamorano | first3 = J. | title = Monitoring Long-Term Trends in the Anthropogenic Night Sky Brightness  | journal = Sustainability | volume = 11 | issue = 11 | page = 3070 | year = 2019 | doi = 10.3390/su11113070 | doi-access = free
 | bibcode = 2019Sust...11.3070B
 | hdl = 10316/107395 | hdl-access = free }}</ref> In Italy, SQM data have been used to monitor urban and protected areas.<ref>{{Cite journal | last1 = Bertolo | first1 = A. | last2 = Binotto | first2 = R.
 | last3 = Ortolani | first3 = S. | last4 = Sapienza | first4 = S. | title = Measurements of Night Sky Brightness in the Veneto Region of Italy: Sky Quality Meter Network Results and Differential Photometry by Digital Single Lens Reflex
 | journal = Journal of Imaging | volume = 5 | issue = 5 | page = 56 | year = 2019 | doi = 10.3390/jimaging5050056
 | doi-access = free | pmid = 34460494 | pmc = 8320935 }}</ref> The Netherlands also maintains a national monitoring program using SQMs to track long-term trends.<ref>{{Cite web | last1 = Schmidt | first1 = T. S. | last2 = Spoelstra | first2 = H. | title = Darkness monitoring in the Netherlands 2009-2019 | date = 2020
 | url = https://zenodo.org/record/4293366 | doi = 10.5281/zenodo.4293366 | access-date = 8 May 2025}}</ref>

These ground-based networks provide continuous data under varied weather conditions and offer a crucial complement to satellite observations, especially for evaluating local lighting policies and environmental impacts.

=== Bortle scale ===
The [[Bortle scale]] is a nine-level measuring system used to track how much light pollution there is in the sky. A Bortle scale of four or less is required to see the [[Milky Way]] whilst one is "pristine", the darkest possible.<ref>{{Cite web|url=https://www.forbes.com/sites/startswithabang/2016/06/14/the-milky-way-invisible-to-most-of-us-but-accessible-to-all/|title=The Milky Way: Invisible To Most Of Us, But Accessible To All|last=Siegel|first=Ethan|date=June 14, 2016|website=[[Forbes]]|access-date=November 16, 2019|archive-date=March 11, 2021|archive-url=https://web.archive.org/web/20210311005605/https://www.forbes.com/sites/startswithabang/2016/06/14/the-milky-way-invisible-to-most-of-us-but-accessible-to-all/|url-status=live}}</ref>

== Global impact ==
[[File:World light pollution.jpg|thumb|upright=2.25|World map of light pollution. False colors show intensities of [[skyglow]] from artificial light sources around the world.]]
[[File:YOUTUBE HQ-12573 blackmarble 2017 youtube hq.webm|thumb|NASA video of a nighttime view of Earth, dubbed the Black Marble<ref>{{cite web |title=NASA's Black Marble |url=https://blackmarble.gsfc.nasa.gov/ |website=blackmarble.gsfc.nasa.gov |access-date=20 September 2024}}</ref>]]

=== Europe ===
Inspection of the area surrounding Madrid reveals that the effects of light pollution caused by a single large conglomeration can be felt up to {{convert|100|km|0|abbr=on}} away from the center.<ref name="NWA" />

Global effects of light pollution are also made obvious. Research in the late 1990s showed that the entire area consisting of southern England, Netherlands, Belgium, West Germany, and northern France have a sky brightness of at least two to four times normal.<ref name="NWA" /> The only places in continental Europe where the sky can attain its natural darkness are in northern Scandinavia and in islands far from the continent.{{citation needed|reason=The image shows large dark areas in the eastern Kola peninsula and Nenetsia. |date=November 2021}} The growth of light pollution on the green band has been 11% from 2012–2013 to 2014–2020, and 24% on the blue band.<ref>{{Cite journal |last1=Sánchez de Miguel |first1=Alejandro |last2=Bennie |first2=Jonathan |last3=Rosenfeld |first3=Emma |last4=Dzurjak |first4=Simon |last5=Gaston |first5=Kevin J. |date=2022-09-16 |title=Environmental risks from artificial nighttime lighting widespread and increasing across Europe |journal=Science Advances |language=en |volume=8 |issue=37 |article-number=eabl6891 |doi=10.1126/sciadv.abl6891 |pmid=36103525 |pmc=9473566 |bibcode=2022SciA....8L6891S |issn=2375-2548}}</ref>

=== North America ===
In North America the situation is comparable. There is a significant problem with light pollution ranging from the Canadian Maritime Provinces to the American Southwest.<ref name="NWA" /> The [[International Dark-Sky Association]] works to designate areas that have high-quality night skies. These areas are supported by communities and organizations that are dedicated to reducing light pollution (e.g. [[Dark-sky preserve]]). The [[National Park Service]] [[Natural Sounds and Night Skies Division]] has measured night sky quality in national park units across the U.S. Sky quality in the U.S. ranges from pristine ([[Capitol Reef National Park]] and [[Big Bend National Park]]) to severely degraded ([[Santa Monica Mountains National Recreation Area]] and [[Biscayne National Park]]).<ref>{{cite journal|author1=Duriscoe D. |author2=Luginbuhl C. |author3=Moore C. |title= Measuring Night Sky Brightness with a Wide-Field CCD Camera|doi=10.1086/512069|arxiv=astro-ph/0702721|bibcode=2007PASP..119..192D|volume=119|issue=852 |journal=Publications of the Astronomical Society of the Pacific|pages=192–213|year=2007 |s2cid=53331822 }}</ref> The National Park Service Night Sky Program monitoring database is available online (2015).<ref>[https://www.nps.gov/subjects/nightskies/index.htm Night Sky Monitoring Database] . nature.nps.gov</ref>

=== East Asia ===
[[Light pollution in Hong Kong]] was declared the 'worst on the planet' in March 2013.<ref>[https://www.scmp.com/news/hong-kong/article/1194996/light-pollution-hong-kong-worst-planet South China Morning Post] {{Webarchive|url=https://web.archive.org/web/20201112033924/http://www.scmp.com/news/hong-kong/article/1194996/light-pollution-hong-kong-worst-planet |date=2020-11-12 }}. 2013-20-3. Retrieved 2013-6-4</ref>

In June 2016, it was estimated that one third of the world's population could no longer see the Milky Way, including 80% of Americans and 60% of Europeans. [[Singapore]] was found to be the most light-polluted country in the world.<ref name="limitednight">{{Cite news|url=http://www.pressherald.com/2016/06/11/light-pollution-limiting-night-sky-views/|first=Brady|last=Dennis|date=June 11, 2016|access-date=June 12, 2016|title=Light pollution limiting night-sky views|publisher=Portland Press Herald, via Washington Post|archive-date=April 25, 2020|archive-url=https://web.archive.org/web/20200425115725/https://www.pressherald.com/2016/06/11/light-pollution-limiting-night-sky-views/|url-status=live}}</ref><ref name="NWA">{{Cite journal|last1=Falchi|first1=Fabio|last2=Cinzano|first2=Pierantonio|last3=Duriscoe|first3=Dan|last4=Kyba|first4=Christopher C. M.|last5=Elvidge|first5=Christopher D.|last6=Baugh|first6=Kimberly|last7=Portnov|first7=Boris A.|last8=Rybnikova|first8=Nataliya A.|last9=Furgoni|first9=Riccardo|date=2016-06-01|title=The new world atlas of artificial night sky brightness|journal=Science Advances |volume=2|issue=6|article-number=e1600377|doi=10.1126/sciadv.1600377|issn=2375-2548|pmid=27386582|pmc=4928945|arxiv = 1609.01041 |bibcode = 2016SciA....2E0377F }}</ref>

Over the past 21 years, China's provincial capital cities have seen a major increase in light pollution, with hotspots along the eastern coastline region.<ref>{{Cite journal |last1=Jiang |first1=Wei |last2=He |first2=Guojin |last3=Long |first3=Tengfei |last4=Wang |first4=Chen |last5=Ni |first5=Yuan |last6=Ma |first6=Ruiqi |date=2017-02-06 |title=Assessing Light Pollution in China Based on Nighttime Light Imagery |journal=Remote Sensing |language=en |volume=9 |issue=2 |page=135 |doi=10.3390/rs9020135 |bibcode=2017RemS....9..135J |issn=2072-4292|doi-access=free }}</ref>

==Consequences==
Light pollution has "detrimental impacts on wildlife, human health, and ecosystem functions and services". Only the damage to ecosystems is estimated as 3.36 trillion dollars per year. Ecosystems which are suffering from the highest level of light pollution, deliver 40% less ecological services.<ref>{{cite journal |last1=Yu |first1=Bailang |last2=Chen |first2=Yunhao |last3=J. Anderson |first3=Sharolyn |last4=Kubiszewski |first4=Ida |last5=C. Sutton |first5=Paul |title=The Ecological Economics of Light Pollution: Impacts on Ecosystem Service Value |journal=Remote Sensing |date=15 July 2024 |volume=16 |issue=Remote Sensing and GIS Technologies for Sustainable Ecosystem Management |page=2591 |doi=10.3390/rs16142591 |doi-access=free |bibcode=2024RemS...16.2591A |hdl=11541.2/39748 |hdl-access=free }}</ref>

=== Public health impact ===

{{see also|Light effects on circadian rhythm|Ecological light pollution}}
[[File:Lichtverschmutzung in Kastelruth.JPG|thumb|right|Streetlights at the ski resort [[Kastelruth]] in [[South Tyrol]], Italy]]

Medical research on the effects of excessive light on the human body suggests that a variety of adverse health effects may be caused by light pollution or excessive light exposure, and some lighting design textbooks<ref>Gary Steffy, ''Architectural Lighting Design'', John Wiley and Sons (2001) {{ISBN|0-471-38638-3}}.</ref> use human health as an explicit criterion for proper interior lighting. Health effects of over-illumination or improper spectral composition of light may include: increased headache incidence, worker [[fatigue (physical)|fatigue]], [[stress (medicine)|medically defined stress]], decrease in [[Human sexuality|sexual]] function and increase in anxiety.<ref>{{Cite journal |last=Rajkhowa |first=Rasna |date=2014 |title=Light Pollution and Impact of Light Pollution |url=https://d1wqtxts1xzle7.cloudfront.net/87472490/T0NUMTQyMTA_-libre.pdf?1655167711=&response-content-disposition=inline%3B+filename%3DLight_Pollution_and_Impact_of_Light_Poll.pdf&Expires=1711526208&Signature=JgCjCdabA5biUDvw1GF7dPaMfpgGGlYOxBIoD4K7sRWbGmAfL0CCWkQPbPD2AM1l8-nfahO0oubK04sdsOT7UUklLAvEOa-Ljel6S2Yah3yI~~nt7PqkK91JO09BB7JXpsFj4l0cUfa0~c6rNno5jAQ-sjnnDU9omC9NrrvqT9zDWxPG5-IYUbfHWg9hXsqKTnTqkafL3FGIg29XtxjVg0rxZhq3J-TaQvaJ-1XWqRGQTJS3R4st-UMUdmtfyhvS0QFoXus7GbKENt6hdgR2uDW76Pfbz~OLlTIg0q1AlttjNw-mi7uTZCH5Lad3Tyb2M1QmwPCvNjWkmxaUqVCtKQ__&Key-Pair-Id=APKAJLOHF5GGSLRBV4ZA |journal=International Journal of Science and Research |volume=3 |issue=10 |pages=861–867 |access-date=2024-03-27 |archive-date=2024-03-27 |archive-url=https://web.archive.org/web/20240327070224/https://d1wqtxts1xzle7.cloudfront.net/87472490/T0NUMTQyMTA_-libre.pdf?1655167711=&response-content-disposition=inline%3B+filename%3DLight_Pollution_and_Impact_of_Light_Poll.pdf&Expires=1711526208&Signature=JgCjCdabA5biUDvw1GF7dPaMfpgGGlYOxBIoD4K7sRWbGmAfL0CCWkQPbPD2AM1l8-nfahO0oubK04sdsOT7UUklLAvEOa-Ljel6S2Yah3yI~~nt7PqkK91JO09BB7JXpsFj4l0cUfa0~c6rNno5jAQ-sjnnDU9omC9NrrvqT9zDWxPG5-IYUbfHWg9hXsqKTnTqkafL3FGIg29XtxjVg0rxZhq3J-TaQvaJ-1XWqRGQTJS3R4st-UMUdmtfyhvS0QFoXus7GbKENt6hdgR2uDW76Pfbz~OLlTIg0q1AlttjNw-mi7uTZCH5Lad3Tyb2M1QmwPCvNjWkmxaUqVCtKQ__&Key-Pair-Id=APKAJLOHF5GGSLRBV4ZA }}</ref><ref name="Burks">Burks, Susan L. (1994) ''Managing your Migraine'', Humana Press, New Jersey. {{ISBN|0-89603-277-9}}.</ref><ref name="Cambridge">''Cambridge Handbook of Psychology, Health and Medicine'', edited by Andrew Baum, Robert West, John Weinman, Stanton Newman, Chris McManus, Cambridge University Press (1997) {{ISBN|0-521-43686-9}}</ref><ref name="Pijnenburg">Pijnenburg, L.; Camps, M. and Jongmans-Liedekerken, G. (1991) ''Looking closer at assimilation lighting'', Venlo, GGD, Noord-Limburg</ref><ref name="Knez">{{cite journal|last1=Knez|first1=I|title=Effects of colour of light on nonvisual psychological processes|journal=Journal of Environmental Psychology|volume=21|pages=201–208|date=2001|doi=10.1006/jevp.2000.0198|issue=2}}</ref> Likewise, animal models have been studied demonstrating unavoidable light to produce adverse effect on mood and anxiety.<ref name="sadrodents">{{Cite journal |last1=Fonken |first1=L K |last2=Finy |first2=M S |title=Influence of light at night on murine anxiety- and depressive-like responses |journal = Behavioural Brain Research| volume = 205 |issue=2 | pages = 349–354 | date = 28 December 2009| doi =10.1016/j.bbr.2009.07.001|last3 = Walton| first3 = James C.| last4 = Weil| first4 = Zachary M.| last5 = Workman| first5 = Joanna L.| last6 = Ross| first6 = Jessica| last7 = Nelson| first7 = Randy J.| pmid = 19591880|s2cid=4204514 }}</ref> For those who need to be awake at night, light at night also has an acute effect on alertness and mood.<ref>{{cite journal|doi=10.1177/1477153509360887|date=2010 |author=Plitnick B |author2=Figueiro MG |author3=Wood B |author4=Rea MS|journal=Lighting Research and Technology|title=The effects of long-wavelength red and short-wavelength blue lights on alertness and mood at night|volume=42|issue=4|pages=449–458|s2cid=54032781 }}</ref>

Outdoor artificial light at night – exposure to contemporary types such as current types of street lighting – has been linked to risks for obesity,<ref>{{cite journal |last1=Park |first1=Yong-Moon Mark |last2=White |first2=Alexandra J. |last3=Jackson |first3=Chandra L. |last4=Weinberg |first4=Clarice R. |last5=Sandler |first5=Dale P. |title=Association of Exposure to Artificial Light at Night While Sleeping With Risk of Obesity in Women |journal=JAMA Internal Medicine |date=1 August 2019 |volume=179 |issue=8 |pages=1061–1071 |doi=10.1001/jamainternmed.2019.0571|pmid=31180469 |pmc=6563591 }}</ref> mental disorders,<ref>{{cite journal |last1=Tancredi |first1=Stefano |last2=Urbano |first2=Teresa |last3=Vinceti |first3=Marco |last4=Filippini |first4=Tommaso |title=Artificial light at night and risk of mental disorders: A systematic review |journal=Science of the Total Environment |date=August 2022 |volume=833 |article-number=155185 |doi=10.1016/j.scitotenv.2022.155185|pmid=35417728 |bibcode=2022ScTEn.83355185T |s2cid=248093823 |hdl=11380/1273458 |hdl-access=free }}</ref> [[diabetes]],<ref>{{cite journal |last1=Zheng |first1=Ruizhi |last2=Xin |first2=Zhuojun |last3=Li |first3=Mian |last4=Wang |first4=Tiange |last5=Xu |first5=Min |last6=Lu |first6=Jieli |last7=Dai |first7=Meng |last8=Zhang |first8=Di |last9=Chen |first9=Yuhong |last10=Wang |first10=Shuangyuan |last11=Lin |first11=Hong |last12=Wang |first12=Weiqing |last13=Ning |first13=Guang |last14=Bi |first14=Yufang |last15=Zhao |first15=Zhiyun |last16=Xu |first16=Yu |title=Outdoor light at night in relation to glucose homoeostasis and diabetes in Chinese adults: a national and cross-sectional study of 98,658 participants from 162 study sites |journal=Diabetologia |date=14 November 2022 |volume=66 |issue=2 |pages=336–345 |doi=10.1007/s00125-022-05819-x |pmid=36372821 |s2cid=253509635 |language=en |issn=1432-0428|doi-access=free }}</ref> and potentially other health issues<ref>{{cite journal |title=Artificial Light at Night: State of the Science 2022 |url=https://www.darksky.org/wp-content/uploads/2022/06/IDA-State-of-the-Science-2022-EN.pdf |publisher=International Dark-Sky Association |access-date=17 December 2022 |doi=10.5281/zenodo.6903500 |date=9 June 2022 |last1=Barentine |first1=John C. |archive-date=1 April 2023 |archive-url=https://web.archive.org/web/20230401022338/https://www.darksky.org/wp-content/uploads/2022/06/IDA-State-of-the-Science-2022-EN.pdf |url-status=live }}</ref> by preliminary studies.<ref>{{cite journal |last1=Zielinska-Dabkowska |first1=K. M. |last2=Schernhammer |first2=E. S. |last3=Hanifin |first3=J. P. |last4=Brainard |first4=G. C. |title=Reducing nighttime light exposure in the urban environment to benefit human health and society |journal=[[Science (journal)|Science]] |date=2023 |volume=380 |issue=6650 |pages=1130–1135 |doi=10.1126/science.adg5277|pmid=37319219 |bibcode=2023Sci...380.1130Z |s2cid=259166063 }}</ref>

In 2007, "shift work that involves circadian disruption" was listed as a probable [[carcinogen]] by the World Health Organization's [[International Agency for Research on Cancer]]. (IARC Press release No. 180).<ref>{{cite web| title = IARC Monographs Programme finds cancer hazards associated with shiftwork, painting and firefighting, International Agency for Research on Cancer| access-date = 2011-07-06| url = http://www.iarc.fr/en/media-centre/pr/2007/pr180.html| archive-url = https://web.archive.org/web/20110721001355/http://www.iarc.fr/en/media-centre/pr/2007/pr180.html| archive-date = 2011-07-21}}</ref><ref>{{cite book| title = IARC Monograph 98| access-date = 2011-07-06| url = http://monographs.iarc.fr/ENG/Monographs/vol98/index.php| archive-date = 2018-06-15| archive-url = https://web.archive.org/web/20180615141748/http://monographs.iarc.fr/ENG/Monographs/vol98/index.php| url-status = live}}</ref> Multiple studies have documented a correlation between night shift work and the increased incidence of breast and prostate cancer.<ref>{{cite journal|last1=Schernhammer|first1=ES|last2=Schulmeister|first2=K|title=Melatonin and cancer risk: does light at night compromise physiologic cancer protection by lowering serum melatonin levels?|journal=British Journal of Cancer|volume=90|issue=5|pages=941–3|date=2004|pmid=14997186|pmc=2409637|doi=10.1038/sj.bjc.6601626}}</ref><ref>{{cite journal|last1=Hansen|first1=J|title=Increased breast cancer risk among women who work predominantly at night|journal=Epidemiology |volume=12|issue=1|pages=74–7|date=2001|pmid=11138824|doi=10.1097/00001648-200101000-00013|s2cid=34390800|doi-access=free}}</ref><ref>{{cite journal|doi=10.1093/jnci/93.20.1557 |pmid=11604479 |last1=Davis |first1=S |date=2001 |pages=1557–62 |issue=20 |last2=Mirick |volume=93 |journal=Journal of the National Cancer Institute |first2=DK |last3=Stevens |first3=RG |title=Night shift work, light at night, and risk of breast cancer |url=http://depts.washington.edu/epidem/Epi591/JNCI%20Editorial.pdf |archive-url=https://web.archive.org/web/20120513142946/http://depts.washington.edu/epidem/Epi591/JNCI%20Editorial.pdf |archive-date=2012-05-13 |doi-access=free }}</ref><ref>{{cite journal|doi=10.1093/jnci/93.20.1563|last1=Schernhammer|first1=ES|last2=Laden|first2=F|last3=Speizer|first3=FE|last4=Willett|first4=WC|last5=Hunter|first5=DJ|last6=Kawachi|first6=I|last7=Colditz|first7=GA|title=Rotating night shifts and risk of breast cancer in women participating in the nurses' health study|journal=Journal of the National Cancer Institute|volume=93|issue=20|pages=1563–8|date=2001|pmid=11604480|doi-access=free}}</ref><ref>{{cite journal|pmid=16596289|last1=Bullough|first1=JD|date=2006|pages=375–83|issue=4|last2=Rea|volume=17|first2=MS|journal=Cancer Causes & Control|last3=Figueiro|first3=MG|title=Of mice and women: light as a circadian stimulus in breast cancer research|url=http://www.lrc.rpi.edu/programs/lightHealth/pdf/ofmiceandwomen.pdf|doi=10.1007/s10552-005-0574-1|s2cid=13069747|access-date=2010-09-29|archive-date=2019-05-16|archive-url=https://web.archive.org/web/20190516062212/https://www.lrc.rpi.edu/programs/lightHealth/pdf/ofmiceandwomen.pdf}}</ref><ref>{{cite journal|pmid=19142761
|last1=Kloog|first1=I|date=2009|pages=108–25|issue=1|last2=Haim|volume=26|first2=A|journal=Chronobiology International|last3=Stevens|first3=RG|last4=Portnov|first4=BA|title=Global co-distribution of light at night (LAN) and cancers of prostate, colon, and lung in men|doi=10.1080/07420520802694020|s2cid=16501239}}</ref> One study which examined the link between exposure to artificial light at night (ALAN) and levels of [[breast cancer]] in South Korea found that regions which had the highest levels of ALAN reported the highest number of cases of breast cancer. Seoul, which had the highest levels of light pollution, had 34.4% more cases of breast cancer than Ganwon-do, which had the lowest levels of light pollution. This suggested a high correlation between ALAN and the prevalence of breast cancer. It was also found that there was no correlation between other types of cancer such as cervical or lung cancer and ALAN levels.<ref>{{Cite journal|last=Yun Jeong|display-authors=etal|date=2015|title=High prevalence of breast cancer in light polluted areas in urban and rural regions of South Korea:An ecologic study on the treatment prevalence of female cancers based on National Health Insurance data.|journal=Chronobiology International|volume=32|issue=5|pages=657–667|doi=10.3109/07420528.2015.1032413|pmid=25955405|s2cid=38132259|url=https://figshare.com/articles/dataset/High_prevalence_of_breast_cancer_in_light_polluted_areas_in_urban_and_rural_regions_of_South_Korea_An_ecologic_study_on_the_treatment_prevalence_of_female_cancers_based_on_National_Health_Insurance_data/1568204|access-date=2021-10-01|archive-date=2022-05-28|archive-url=https://web.archive.org/web/20220528102753/https://figshare.com/articles/dataset/High_prevalence_of_breast_cancer_in_light_polluted_areas_in_urban_and_rural_regions_of_South_Korea_An_ecologic_study_on_the_treatment_prevalence_of_female_cancers_based_on_National_Health_Insurance_data/1568204|url-status=live|url-access=subscription}}</ref>

A more recent discussion (2009), written by Professor Steven Lockley, Harvard Medical School, can be found in the CfDS handbook "Blinded by the Light?".<ref>{{cite web |url=http://www.britastro.org/dark-skies/handbook.html |title=CfDS Handbook |publisher=Britastro.org |access-date=2010-09-04 |archive-url=https://web.archive.org/web/20100617011039/http://www.britastro.org/dark-skies/handbook.html |archive-date=2010-06-17 }}</ref> Chapter 4, "Human health implications of light pollution" states that "...{{nbsp}}light intrusion, even if dim, is likely to have measurable effects on sleep disruption and [[melatonin]] suppression. Even if these effects are relatively small from night to night, continuous chronic circadian, sleep and hormonal disruption may have longer-term health risks". The New York Academy of Sciences hosted a meeting in 2009 on Circadian Disruption and Cancer.<ref>{{cite web |url=http://network.nature.com/hubs/nyc/events/8335 |title=Event—Circadian Disruption and Cancer on Nature Network |publisher=Network.nature.com |access-date=2010-09-04 |archive-url=https://web.archive.org/web/20110512162244/http://network.nature.com/hubs/nyc/events/8335 |archive-date=2011-05-12 }}</ref> In different wavelengths of light, red light has the least inhibitory effect on melatonin.<ref>{{Cite journal |last=Chepesiuk |first=Ron |date=January 2009 |title=Missing the Dark: Health Effects of Light Pollution |journal=Environmental Health Perspectives |language=en |volume=117 |issue=1 |pages=A20-7 |doi=10.1289/ehp.117-a20 |issn=0091-6765 |pmc=2627884 |pmid=19165374}}</ref><ref name="uchc">{{cite web| last = Cheung| first = Maria| title = Graveyard Shift Work Linked to Cancer| work = news| publisher = University of Connecticut Health Center| date = 2009-11-29| url = http://today.uchc.edu/headlines/2007/nov07/graveyard| access-date = 2012-07-06| archive-date = 2020-11-27| archive-url = https://web.archive.org/web/20201127030939/http://today.uchc.edu/headlines/2007/nov07/graveyard/| url-status = live}}</ref>

In June 2009, the [[American Medical Association]] developed a policy in support of control of light pollution. News about the decision emphasized [[glare (vision)|glare]] as a [[public health]] hazard leading to unsafe driving conditions. Especially in the elderly, glare produces loss of contrast, obscuring night vision.<ref name="Motta-2009" />

A new 2021 study published in the Southern Economic Journal indicates that light pollution may increase by 13% in preterm births before 23 weeks of gestation.<ref>{{cite journal |title=Light pollution, sleep deprivation, and infant health at birth |url=https://onlinelibrary.wiley.com/doi/10.1002/soej.12477 |journal=Southern Economic Journal |year=2021 |doi=10.1002/soej.12477 |access-date=4 March 2021 |last1=Argys |first1=Laura M. |last2=Averett |first2=Susan L. |last3=Yang |first3=Muzhe |volume=87 |issue=3 |pages=849–888 |hdl=10419/185163 |s2cid=92984550 |hdl-access=free |archive-date=17 April 2021 |archive-url=https://web.archive.org/web/20210417152759/https://onlinelibrary.wiley.com/doi/10.1002/soej.12477 |url-status=live |url-access=subscription }}</ref>

=== Ecological impact ===

{{Main|Ecological light pollution}}

While light at night can be beneficial, neutral, or damaging for individual [[species]], its presence invariably disturbs ecosystems. For example, some species of spiders avoid lit areas, while other species are happy to build their [[spider web|webs]] directly on lamp posts. Since lamp posts attract many flying insects, the spiders that tolerate the light gain an advantage over the spiders that avoid it. This is a simple example of the way in which species frequencies and [[food web]]s can be disturbed by the introduction of light at night.

Light pollution poses a serious threat in particular to [[Nocturnality|nocturnal]] wildlife, having negative impacts on plant and animal physiology.<ref>{{cite journal |last1=Jägerbrand |first1=Annika K. |last2=Spoelstra |first2=Kamiel |title=Effects of anthropogenic light on species and ecosystems |journal=[[Science (journal)|Science]] |date=2023 |volume=380 |issue=6650 |pages=1125–1130 |doi=10.1126/science.adg3173|pmid=37319223 |bibcode=2023Sci...380.1125J |s2cid=259166091 |url=https://pure.knaw.nl/portal/en/publications/3f82a70f-504f-4b1a-93bf-bde72a20e2ee |hdl=20.500.11755/3f82a70f-504f-4b1a-93bf-bde72a20e2ee |hdl-access=free }}</ref> It can confuse [[animal navigation]], alter competitive interactions, change predator-prey relations,<ref>{{Cite journal |last1=McMahon |first1=Oak |last2=Smyth |first2=Tim |last3=Davies |first3=Thomas W. |date=2022-03-25 |title=Broad spectrum artificial light at night increases the conspicuousness of camouflaged prey |journal=Journal of Applied Ecology |volume=59 |issue=5 |language=en |pages=1365–2664.14146 |doi=10.1111/1365-2664.14146 |s2cid=247754178 |issn=0021-8901|doi-access=free |bibcode=2022JApEc..59.1324M |hdl=10026.1/18654 |hdl-access=free }}</ref> and cause physiological harm.<ref name="Perry-2008">{{Cite book| last1=Perry| first1=G.| last2=Buchanan| first2=B. W.| last3=Fisher| first3=R. N.| last4=Salmon| first4=M.| last5=Wise| first5=S. E.| chapter=Effects of artificial night lighting on amphibians and reptiles in urban environments| date=2008| editor1-first=J. C.| editor2-first=R. E. J.| editor3-first=B.| title=Urban Herpetology| volume=3| pages=239–256| publisher=Society for the Study of Amphibians and Reptiles| publication-date=2008| isbn=978-0-916984-79-3| editor2-last=Mitchell| editor3-last=Brown| editor1-last=Bartholomew}}</ref> The rhythm of life is orchestrated by the natural diurnal patterns of light and dark, so disruption to these patterns impacts the ecological dynamics.<ref>{{cite journal|doi=10.1890/1540-9295(2004)002[0191:ELP]2.0.CO;2|url=http://www.urbanwildlands.org/Resources/LongcoreRich2004.pdf|title=Ecological light pollution|journal=Frontiers in Ecology and the Environment|date=2004|volume=2|issue=4|pages=191–198|last1=Longcore|first1=Travis|last2=Rich|first2=Catherine|doi-access=free|access-date=2005-07-29|archive-date=2011-05-12|archive-url=https://web.archive.org/web/20110512162227/http://www.urbanwildlands.org/Resources/LongcoreRich2004.pdf|url-status=live}}</ref> Many species of marine plankton, such as ''Calanus'' copepods, can detect light levels as low as 0.1 μWm<sup>−2</sup>;<ref>{{Cite journal |last1=Båtnes |first1=Anna S. |last2=Miljeteig |first2=Cecilie |last3=Berge |first3=Jørgen |last4=Greenacre |first4=Michael |last5=Johnsen |first5=Geir |date=January 2015 |title=Quantifying the light sensitivity of Calanus spp. during the polar night: potential for orchestrated migrations conducted by ambient light from the sun, moon, or aurora borealis? |url=http://link.springer.com/10.1007/s00300-013-1415-4 |journal=Polar Biology |language=en |volume=38 |issue=1 |pages=51–65 |doi=10.1007/s00300-013-1415-4 |bibcode=2015PoBio..38...51B |s2cid=11754884 |issn=0722-4060|url-access=subscription }}</ref> using this as a threshold a global atlas of marine Artificial Light at Night has been generated,<ref>{{Cite journal |last1=Smyth |first1=T. J. |last2=Wright |first2=A. E. |last3=McKee |first3=D. |last4=Tidau |first4=S. |last5=Tamir |first5=R. |last6=Dubinsky |first6=Z. |last7=Iluz |first7=D. |last8=Davies |first8=T. W. |date=2021-12-13 |title=A global atlas of artificial light at night under the sea |journal=Elementa: Science of the Anthropocene |volume=9 |issue=1 |page=00049 |doi=10.1525/elementa.2021.00049 |bibcode=2021EleSA...9...49S |s2cid=245169968 |issn=2325-1026|doi-access=free |hdl=10037/24006 |hdl-access=free }}</ref> showing its global widespread nature.

Studies suggest that light pollution around lakes prevents zooplankton, such as ''[[Daphnia]]'', from eating surface [[algae]], causing [[algal bloom]]s that can kill off the lakes' plants and lower water quality.<ref>{{cite journal| author=Moore, Marianne V.| author2=Pierce, Stephanie M.| author3=Walsh, Hannah M.| author4=Kvalvik, Siri K.| author5=Julie D. Lim| name-list-style=amp| url=http://www.wellesley.edu/Biology/Faculty/Mmoore/Content/Moore_2000.pdf| title=Urban light pollution alters the diel vertical migration of Daphnia| journal=Verh. Internat. Verein. Limnol| volume=27| date=2000| issue=2| page=779| doi=10.1080/03680770.1998.11901341| bibcode=2000SILP...27..779M| access-date=2005-05-29| archive-date=2005-10-21| archive-url=https://web.archive.org/web/20051021232549/http://www.wellesley.edu/Biology/Faculty/Mmoore/Content/Moore_2000.pdf}}</ref> Light pollution may also affect ecosystems in other ways. For example, [[entomologist]]s have documented that nighttime light may interfere with the ability of moths and other nocturnal insects to navigate.<ref>{{cite journal|author=Frank, Kenneth D.|url=http://www.darksky.org/infoshts/is109.html|title=Impact of outdoor lighting on moths|journal=Journal of the Lepidopterists' Society|date=1988|volume=42|pages=63–93|archive-url=https://web.archive.org/web/20060617110107/http://www.darksky.org/infoshts/is109.html|archive-date=2006-06-17}}</ref> It can also negative impact on insect development and reproduction.<ref>{{Cite journal|last1=Boyes|first1=Douglas H.|last2=Evans|first2=Darren M.|last3=Fox|first3=Richard|last4=Parsons|first4=Mark S.|last5=Pocock|first5=Michael J. O.|date=2021|title=Is light pollution driving moth population declines? A review of causal mechanisms across the life cycle|journal=Insect Conservation and Diversity|language=en|volume=14|issue=2|pages=167–187|doi=10.1111/icad.12447|s2cid=224956373|issn=1752-4598|doi-access=free}}</ref> Night-blooming flowers that depend on moths for [[pollination]] may be affected by night lighting, as there is no replacement [[pollinator]] that would not be affected by the artificial light. This can lead to species decline of plants that are unable to reproduce, and change an area's longterm [[ecology]].<ref>[https://www.theatlantic.com/science/archive/2017/08/confirmed-night-lights-drive-pollinators-away-from-plants/535983/ Confirmed: Night Lights Drive Pollinators Away From Plants] {{Webarchive|url=https://web.archive.org/web/20180708104417/https://www.theatlantic.com/amp/article/535983/ |date=2018-07-08 }} The Atlantic, 2017</ref> Among nocturnal insects, [[Firefly|fireflies]] ([[Beetle|Coleoptera]]: Lampyridae, Phengodidae and Elateridae) are especially interesting study objects for light pollution, once they depend on their own light to reproduce and, consequently, are very sensitive to environmental levels of light.<ref name="Longcore, Travis-2006" /><ref>{{Cite journal|last1=Lloyd|first1=James E.|last2=Wing|first2=Steven R.|last3=Hongtrakul|first3=Tawatchai|date=1989|title=Ecology, Flashes, and Behavior of Congregating Thai Fireflies|jstor=2388290|journal=Biotropica|volume=21|issue=4|pages=373–376|doi=10.2307/2388290|bibcode=1989Biotr..21..373L }}</ref><ref>{{Cite journal|last1=Firebaugh|first1=Ariel|last2=Haynes|first2=Kyle J.|date=2016-12-01|title=Experimental tests of light-pollution impacts on nocturnal insect courtship and dispersal|journal=Oecologia|language=en|volume=182|issue=4|pages=1203–1211|doi=10.1007/s00442-016-3723-1|issn=0029-8549|bibcode=2016Oecol.182.1203F|pmid=27646716|s2cid=36670391}}</ref> Fireflies are well known and interesting to the general public (unlike many other insects)<ref>{{Cite journal|last1=Picchi|first1=Malayka Samantha|last2=Avolio|first2=Lerina|last3=Azzani|first3=Laura|last4=Brombin|first4=Orietta|last5=Camerini|first5=Giuseppe|date=2013-08-01|title=Fireflies and land use in an urban landscape: the case of Luciola italica L. (Coleoptera: Lampyridae) in the city of Turin|journal=Journal of Insect Conservation|language=en|volume=17|issue=4|pages=797–805|doi=10.1007/s10841-013-9562-z|bibcode=2013JICon..17..797P |s2cid=17204044|issn=1366-638X}}</ref> and are easily spotted by non-experts, and, due to their sensibility and rapid response to environmental changes, good [[bioindicator]]s for artificial night lighting.<ref>{{Cite journal|last1=Viviani|first1=Vadim Ravara|last2=Rocha|first2=Mayra Yamazaki|last3=Hagen|first3=Oskar|date=June 2010|title=Bioluminescent beetles (Coleoptera: Elateroidea: Lampyridae, Phengodidae, Elateridae) in the municipalities of Campinas, Sorocaba-Votorantim and Rio Claro-Limeira (SP, Brazil): biodiversity and influence of urban sprawl|journal=Biota Neotropica|volume=10|issue=2|pages=103–116|doi=10.1590/S1676-06032010000200013|issn=1676-0603|doi-access=free}}</ref> Significant declines in some insect populations have been suggested as being at least partially mediated by artificial lights at night.<ref>{{Cite journal|last1=Grubisic|first1=M.|last2=van Grunsven|first2=R.H.A.|last3=Kyba|first3=C.C.M.|last4=Manfrin|first4=A.|last5=Hölker|first5=F.|date=2018-06-11|title=Insect declines and agroecosystems: does light pollution matter?|journal=Annals of Applied Biology|volume=173|issue=2|pages=180–189|language=en|doi=10.1111/aab.12440|s2cid=89892699|issn=0003-4746|url=http://gfzpublic.gfz-potsdam.de/pubman/item/escidoc:3275891|doi-access=free}}</ref><ref>{{Cite journal|last1=Boyes|first1=Douglas H.|last2=Evans|first2=Darren M.|last3=Fox|first3=Richard|last4=Parsons|first4=Mark S.|last5=Pocock|first5=Michael J. O.|date=August 2021|title=Street lighting has detrimental impacts on local insect populations|journal=Science Advances|volume=7|issue=35|article-number=eabi8322|language=EN|doi=10.1126/sciadv.abi8322|pmc=8386932|pmid=34433571|bibcode=2021SciA....7.8322B}}</ref><ref>{{Cite journal|date=2020-01-01|title=Light pollution is a driver of insect declines|url=https://www.sciencedirect.com/science/article/abs/pii/S0006320719307797|journal=Biological Conservation|language=en|volume=241|article-number=108259|doi=10.1016/j.biocon.2019.108259|issn=0006-3207|last1=Owens|first1=Avalon C.S.|last2=Cochard|first2=Précillia|last3=Durrant|first3=Joanna|last4=Farnworth|first4=Bridgette|last5=Perkin|first5=Elizabeth K.|last6=Seymoure|first6=Brett|bibcode=2020BCons.24108259O|s2cid=209570356|access-date=2021-09-18|archive-date=2021-09-18|archive-url=https://web.archive.org/web/20210918115908/https://www.sciencedirect.com/science/article/abs/pii/S0006320719307797|url-status=live|url-access=subscription}}</ref>
[[File:Scorpion in arizona.jpg|thumb|A scorpion hides under rocks.]]
[[File:Birds flying trace.jpg|alt=Birds flying trace and star trail near Rio de Janeiro beach at night time in light pollution|thumb|Birds flying trace and star trail near Rio de Janeiro beach at night time in light pollution]]
[[File:Brazil star trails and birds in light pollution photography in Rio beach at night.jpg|alt=Brazil star trails and birds in light pollution in Rio beach at night|thumb|Brazil star trails and birds in light pollution in Rio beach at night]]

A 2009 study<ref name="PolarizedLightEnv">{{cite journal|author2=Gábor Horváth|author3=György Kriska|author4=Péter Malik|author5=Bruce Robertson|title=Polarized light pollution: a new kind of ecological photopollution|journal=Frontiers in Ecology and the Environment|volume=7|issue=6 |date=August 2009|pages=317–325|doi=10.1890/080129|last1=Horváth|first1=Gábor|doi-access=free|bibcode=2009FrEE....7..317H }}</ref> also suggests deleterious impacts on animals and ecosystems because of perturbation of polarized light or artificial polarization of light (even during the day, because direction of natural polarization of sun light and its reflection is a source of information for a lot of animals). This form of pollution is named [[polarized light pollution]] (PLP). Unnatural polarized light sources can trigger maladaptive behaviors in polarization-sensitive taxa and alter ecological interactions.<ref name="PolarizedLightEnv" />

Lights on tall structures can disorient migrating birds. Estimates by the [[United States Fish and Wildlife Service|U.S. Fish and Wildlife Service]] of the number of birds killed after being attracted to tall towers range from four to five million per year to an order of magnitude higher.<ref>{{cite journal|author=Malakoff, D. |title=Faulty towers|journal=Audubon|date=2001|volume=103|pages=78–83 | issue=5}}</ref> The Fatal Light Awareness Program (FLAP) works with building owners in [[Toronto]], [[Ontario]], Canada and other cities to reduce mortality of birds by turning out lights during migration periods. Another study has found that the lights produced by the [[Post Tower]] has affected 25 bird species. As a result, they discovered that decreasing the use of excessive lights increased the survival rate of bird species.<ref>{{Cite journal |last1=Korner |first1=Pius |last2=von Maravic |first2=Irina |last3=Haupt |first3=Heiko |date=2022-07-01 |title=Birds and the 'Post Tower' in Bonn: a case study of light pollution |journal=Journal of Ornithology |language=en |volume=163 |issue=3 |pages=827–841 |doi=10.1007/s10336-022-01985-2 |s2cid=248788275 |issn=2193-7206|doi-access=free |bibcode=2022JOrni.163..827K }}</ref>

Similar disorientation has also been noted for bird species migrating close to offshore production and drilling facilities. Studies carried out by Nederlandse Aardolie Maatschappij b.v. (NAM) and Shell have led to the development and trial of new lighting technologies in the North Sea. In early 2007, the lights were installed on the Shell production platform L15. The experiment proved a great success since the number of birds circling the platform declined by 50 to 90%.<ref>{{cite web |url=http://www.nam.nl/home/Framework?siteId=nam-nl |title=Welkom op de site van de Nederlandse Aardolie Maatschappij BV |publisher=Nam.nl |date=2009-03-26 |access-date=2010-09-04 |archive-date=2011-02-02 |archive-url=https://web.archive.org/web/20110202233013/http://www.nam.nl/home/Framework?siteId=nam-nl }}</ref>

Birds migrate at night for several reasons. They save water from dehydration in hot day flying, and part of the bird's navigation system works with stars in some way. With city light outshining the night sky, birds (and also about mammals) no longer navigate by stars.<ref>{{Cite web|date=2020-10-15|title=در سایه‌ی نور‌ها|url=https://parisabajelan.com/brazil-birds-and-light-pollution/|access-date=2020-10-16|website=پریسا باجلان|language=fa-IR|archive-date=2021-04-10|archive-url=https://web.archive.org/web/20210410195730/https://parisabajelan.com/brazil-birds-and-light-pollution/}}</ref>

[[Sea turtle]] hatchlings emerging from nests on beaches are another casualty of light pollution. It is a common misconception that hatchling sea turtles are attracted to the moon. Rather, they find the ocean by moving away from the dark silhouette of dunes and their vegetation, a behavior with which artificial lights interfere.<ref>{{cite journal|author=Salmon, M.|url=http://www.seaturtle.org/PDF/Salmon_2003_Biologist.pdf|title=Artificial night lighting and sea turtles|journal=Biologist|date=2003|volume=50|pages=163–168|archive-date=2020-08-20|access-date=2010-09-29|archive-url=https://web.archive.org/web/20200820123507/http://www.seaturtle.org/PDF/Salmon_2003_Biologist.pdf|url-status=dead}}</ref> The breeding activity and reproductive phenology of toads, however, are cued by moonlight.<ref>{{cite journal| title=The lunar cycle: a cue for amphibian reproductive phenology?| journal=Animal Behaviour| volume=78|date=2009|pages=349–357| doi=10.1016/j.anbehav.2009.05.007| issue=2| last1=Grant| first1=Rachel A.| last2=Chadwick| first2=Elizabeth A.| last3=Halliday| first3=Tim| s2cid=53169271}}</ref> Juvenile seabirds are also disoriented by lights as they leave their nests and fly out to sea, causing events of high mortality.<ref>{{cite journal|last1=RodrÍguez|first1=Airam|last2=RodrÍguez|first2=Beneharo|title=Attraction of petrels to artificial lights in the Canary Islands: effects of the moon phase and age class|journal=Ibis|volume=151|pages=299–310|date=2009|doi=10.1111/j.1474-919X.2009.00925.x|issue=2|hdl=10261/45133|hdl-access=free}}</ref><ref>{{Cite journal| doi = 10.1111/j.1469-1795.2012.00544.x| title = Factors affecting mortality of shearwaters stranded by light pollution| journal = Animal Conservation| volume = 15| issue = 5| pages = 519–526| year = 2012| last1 = Rodríguez| first1 = A.| last2 = Rodríguez| first2 = B.| last3 = Curbelo| first3 = Á. J.| last4 = Pérez| first4 = A.| last5 = Marrero| first5 = S.| last6 = Negro| first6 = J. J.| bibcode = 2012AnCon..15..519R| url = https://digital.csic.es/bitstream/10261/60076/1/Rodr%c3%adguez%20et%20al%202012%20Anim%20Conserv.pdf| hdl = 10261/60076| s2cid = 36944990| hdl-access = free| access-date = 2018-04-20| archive-date = 2021-04-15| archive-url = https://web.archive.org/web/20210415095650/https://digital.csic.es/bitstream/10261/60076/1/Rodr%c3%adguez%20et%20al%202012%20Anim%20Conserv.pdf| url-status = live}}</ref><ref>{{Cite journal | doi = 10.1371/journal.pone.0110114| title = Fatal Attraction of Short-Tailed Shearwaters to Artificial Lights| journal = PLOS ONE| volume = 9| issue = 10| article-number = e110114| year = 2014| last1 = Rodríguez | first1 = A. | last2 = Burgan | first2 = G. | last3 = Dann | first3 = P. | last4 = Jessop | first4 = R. | last5 = Negro | first5 = J. J. | last6 = Chiaradia | first6 = A. | pmid=25334014 | pmc=4198200|bibcode = 2014PLoSO...9k0114R | doi-access = free}}</ref><ref>{{cite journal |last1=Rodríguez |first1=Airam |last2=Holmes |first2=Nick D. |last3=Ryan |first3=Peter G. |last4=Wilson |first4=Kerry-Jayne |last5=Faulquier |first5=Lucie |last6=Murillo |first6=Yovana |last7=Raine |first7=André F. |last8=Penniman |first8=Jay F. |last9=Neves |first9=Verónica |last10=Rodríguez |first10=Beneharo |last11=Negro |first11=Juan J. |last12=Chiaradia |first12=André |last13=Dann |first13=Peter |last14=Anderson |first14=Tracy |last15=Metzger |first15=Benjamin |last16=Shirai |first16=Masaki |last17=Deppe |first17=Lorna |last18=Wheeler |first18=Jennifer |last19=Hodum |first19=Peter |last20=Gouveia |first20=Catia |last21=Carmo |first21=Vanda |last22=Carreira |first22=Gilberto P. |last23=Delgado-Alburqueque |first23=Luis |last24=Guerra-Correa |first24=Carlos |last25=Couzi |first25=François-Xavier |last26=Travers |first26=Marc |last27=Corre |first27=Matthieu Le |title=Seabird mortality induced by land-based artificial lights: Seabird Mortality and Artificial Lights |journal=Conservation Biology |date=October 2017 |volume=31 |issue=5 |pages=986–1001 |doi=10.1111/cobi.12900|pmid=28151557 |hdl=10400.3/4515 |hdl-access=free }}</ref> Amphibians and reptiles are also affected by light pollution. Introduced light sources during normally dark periods can disrupt levels of melatonin production. Melatonin is a hormone that regulates photoperiodic physiology and behaviour. Some species of frogs and salamanders utilize a light-dependent "compass" to orient their migratory behaviour to breeding sites. Introduced light can also cause developmental irregularities, such as retinal damage, reduced juvenile growth, premature metamorphosis,<ref>{{Cite journal|last1=Dananay|first1=Kacey L.|last2=Benard|first2=Michael F.|date=2018-07-11|title=Artificial light at night decreases metamorphic duration and juvenile growth in a widespread amphibian|journal=Proc. R. Soc. B|language=en|volume=285|issue=1882|article-number=20180367|doi=10.1098/rspb.2018.0367|pmid=30051829|pmc=6053935|issn=0962-8452}}</ref> reduced sperm production, and genetic mutation.<ref name="Perry-2008" /><ref>{{cite journal|last1=Rowan|first1=William|title=Light and seasonal reproduction in animals|journal=Biological Reviews|volume=13|pages=374–401|date=1938|doi=10.1111/j.1469-185X.1938.tb00523.x|issue=4|s2cid=84548036}}</ref><ref>{{cite journal|author=Scheling, L. |date=2006|title= Ecological Consequences of Artificial Night Lighting|volume=27|issue=3|journal=Natural Areas Journal|pages=281–282|doi=10.3375/0885-8608(2007)27[281:ecoanl]2.0.co;2|s2cid=83768296 }}</ref><ref name="Longcore, Travis-2006">{{cite book|author=Rich, Catherine |author2=Longcore, Travis |name-list-style=amp|title=Ecological consequences of artificial night lighting|publisher=Island Press|date=2006|isbn=978-1-55963-128-0}}</ref><ref>{{cite journal|last1=Woltz|first1=H|last2=Gibbs|first2=J|last3=Ducey|first3=P|title=Road crossing structures for amphibians and reptiles: Informing design through behavioral analysis|journal=Biological Conservation|volume=141|pages=2745–2750|date=2008|doi=10.1016/j.biocon.2008.08.010|issue=11|bibcode=2008BCons.141.2745W|s2cid=82932376|url=http://www.escholarship.org/uc/item/0tm3n517|access-date=2019-01-14|archive-date=2020-02-17|archive-url=https://web.archive.org/web/20200217170314/https://escholarship.org/uc/item/0tm3n517|url-status=live}}</ref><ref>{{cite journal|last1=Barrett|first1=K|last2=Guyer|first2=C|title=Differential responses of amphibians and reptiles in riparian and stream habitats to land use disturbances in western Georgia, USA|journal=Biological Conservation|volume=141|pages=2290–2300|date=2008|doi=10.1016/j.biocon.2008.06.019|issue=9|bibcode=2008BCons.141.2290B}}</ref> Close to global coastal megacities (e.g. Tokyo, Shanghai), the natural illumination cycles provided by the moon in the marine environment are considerably disrupted by light pollution, with only nights around the full moon providing greater radiances, and over a given month lunar dosages may be a factor of 6 less than light pollution dosages.<ref>{{Cite journal |last1=Smyth |first1=T. J. |last2=Wright |first2=A. E. |last3=Edwards-Jones |first3=A. |last4=McKee |first4=D. |last5=Queirós |first5=A. |last6=Rendon |first6=O. |last7=Tidau |first7=S. |last8=Davies |first8=T. W. |date=2022 |title=Disruption of marine habitats by artificial light at night from global coastal megacities |journal=Elementa: Science of the Anthropocene |volume=10 |issue=1 |page=00042 |doi=10.1525/elementa.2022.00042 |bibcode=2022EleSA..10...42S |s2cid=254213236 |issn=2325-1026|doi-access=free |hdl=10037/28198 |hdl-access=free }}</ref>

In September 2009, the 9th European Dark-Sky Symposium in Armagh, Northern Ireland had a session on the environmental effects of light at night (LAN). It dealt with bats, turtles, the "hidden" harms of LAN, and many other topics.<ref>[http://www.ustream.tv/recorded/2181927 Video] {{Webarchive|url=https://web.archive.org/web/20110102120622/http://www.ustream.tv/recorded/2181927 |date=2011-01-02 }}. Ustream.tv. Retrieved 2011-12-03.</ref> The environmental effects of LAN were mentioned as early as 1897, in a ''[[Los Angeles Times]]'' article. The following is an excerpt from that article, called "Electricity and English songbirds":

{{blockquote|An English journal has become alarmed at the relation of electricity to songbirds, which it maintains is closer than that of cats and fodder crops. How many of us, it asks, foresee that electricity may extirpate the songbird?{{nbsp}}... With the exception of the finches, all the English songbirds may be said to be insectivorous, and their diet consists chiefly of vast numbers of very small insects which they collect from the grass and herbs before the dew is dry. As the electric light is finding its way for street illumination into the country parts of England, these poor winged atoms are slain by thousands at each light every warm summer evening.{{nbsp}}... The fear is expressed, that when England is lighted from one end to the other with electricity the songbirds will die out from the failure of their food supply.<ref>{{cite news|title=Electricity and English songbirds|date=14 September 1897|work=[[Los Angeles Times]]}}</ref>}}

===Effect on astronomy===
[[File:Light pollution It's not pretty.jpg|thumb|The constellation [[Orion (constellation)|Orion]], imaged at left from dark skies, and at right from within the Provo/Orem, Utah metropolitan area.]][[Astronomy]] is very sensitive to light pollution. The [[night sky]] viewed from a city bears no resemblance to what can be seen from dark skies.<ref>{{cite web |url=http://ngm.nationalgeographic.com/2008/11/light-pollution/klinkenborg-text |archive-url=https://web.archive.org/web/20081018060653/http://ngm.nationalgeographic.com/2008/11/light-pollution/klinkenborg-text |archive-date=October 18, 2008 |work=[[National Geographic]] |publisher=[[National Geographic Society]] |date=November 2008 |access-date=2011-12-03|title=National Geographic Magazine }}</ref> [[Skyglow]] (the [[Light scattering by particles|scattering of light]] in the atmosphere at night) reduces the contrast between stars and [[Galaxy|galaxies]] and the sky itself, making it much harder to see fainter [[Astronomical object|objects]].<ref>{{Cite web |title=Skyglow |url=https://www.johncbarentine.com/skyglow.html |access-date=2024-04-23 |website=John C. Barentine's Personal Website |language=en |archive-date=2024-04-23 |archive-url=https://web.archive.org/web/20240423205030/https://www.johncbarentine.com/skyglow.html |url-status=live }}</ref> This is one factor that has caused newer [[telescope]]s to be built in increasingly remote areas.

Even at apparent clear night skies, there can be a lot of [[stray light]] that becomes visible at longer [[exposure time]]s in [[astrophotography]]. By means of software, the stray light can be reduced, but at the same time, object detail could be lost in the image.<ref>{{Cite journal |last1=Reegen |first1=P. |last2=Kallinger |first2=T. |last3=Frast |first3=D. |last4=Gruberbauer |first4=M. |last5=Huber |first5=D. |last6=Matthews |first6=J. M. |last7=Punz |first7=D. |last8=Schraml |first8=S. |last9=Weiss |first9=W. W. |last10=Kuschnig |first10=R. |last11=Moffat |first11=A. F. J. |last12=Walker |first12=G. A. H. |last13=Guenther |first13=D. B. |last14=Rucinski |first14=S. M. |last15=Sasselov |first15=D. |date=2006-04-21 |title=Reduction of time-resolved space-based CCD photometry developed for MOST Fabry Imaging data |journal=Monthly Notices of the Royal Astronomical Society |volume=367 |issue=4 |pages=1417–1431 |doi=10.1111/j.1365-2966.2006.10082.x |doi-access=free |issn=0035-8711|arxiv=physics/0703153 }}</ref> The following picture of the area around the [[Pinwheel Galaxy]] (Messier 101) with the [[apparent magnitude]] of 7.5<sup>m</sup> with all stars down to an apparent magnitude of 10<sup>m</sup> was taken in [[Berlin]] in a direction close to the [[zenith]] with a fast lens (f-number 1.2) and an exposure time of five seconds at an [[exposure index]] of ISO 12800:{{clear}}
<gallery widths="540" heights="120" perrow="2" class="center" mode="packed" caption="Pinwheel Galaxy in stray light">
File:Streulichtfilterung.0.P1023258.jpg|Original shot: lower edge [[Eta Ursae Majoris|Alkaid]], right of center the double star [[Mizar]] with [[Alcor (star)|Alcor]] and right edge [[Epsilon Ursae Majoris|Alioth]]; the [[Pinwheel Galaxy]] is a small diffuse dot in the center of the image.
File:Streulichtfilterung.1.P1023258.jpg|Black level compensation: the darkest point in the digital picture was set to zero luminance, in order to reduce the visible stray light. However, blue light caused by [[Rayleigh scattering]] is visible in the center of the image.
File:Streulichtfilterung.2.P1023258.jpg|50 percent of stray light removed: the darker half of the stray light was set to zero luminance. The darker part of the blue light caused by Rayleigh scattering is still visible in the center of the image.
File:Streulichtfilterung.3.P1023258.jpg|Complete elimination of stray light: all pixels showing stray light have been set to zero luminance, the faint and two-dimensional Pinwheel Galaxy is no longer visible, too.
</gallery>

Some astronomers use narrow-band "[[astronomical filter|nebula filters]]", which allow only specific wavelengths of light commonly seen in [[nebula]]e, or broad-band "light pollution filters", which are designed to reduce (but not eliminate) the effects of light pollution by [[optical filter|filtering]] out [[spectral line]]s commonly emitted by [[sodium-vapor lamp|sodium]]- and [[mercury-vapor lamp]]s, thus enhancing contrast and improving the view of dim objects such as galaxies and nebulae.<ref>{{cite web |url=http://www.astronexus.com/node/4 |title=Use of light pollution filters in astronomy |publisher=Astronexus |access-date=2011-12-03 |archive-date=2011-11-12 |archive-url=https://web.archive.org/web/20111112081736/http://www.astronexus.com/node/4 }}</ref> Unfortunately, these light pollution reduction (LPR) filters are not a cure for light pollution. LPR filters reduce the brightness of the object under study and this limits the use of higher magnifications. LPR filters work by blocking light of certain wavelengths, which alters the color of the object, often creating a pronounced green cast. Furthermore, LPR filters work only on certain object types (mainly [[emission nebulae]]) and are of little use on galaxies and stars. No filter can match the effectiveness of a dark sky for visual or [[photographic filter|photographic]] purposes.
[[File:Milky Way Shines over Snowy La Silla.jpg|thumb|The [[Atacama Desert#Astronomical observatories|Atacama Desert]] in northern Chile is far from any cities, and the night sky there is pitch-black. Photo by José Francisco Salgado.<ref>{{cite web |title=Milky Way Shines over Snowy La Silla |url=http://www.eso.org/public/images/potw1319a/ |work=ESO Picture of the Week |access-date=13 May 2013}}</ref>]]

Light pollution affects the visibility of [[deep-sky object|diffuse sky objects]] like nebulae and galaxies more than stars, due to their low surface brightness.<ref>{{Cite journal |last=Varela Perez |first=Antonia M. |date=2023-06-16 |title=The increasing effects of light pollution on professional and amateur astronomy |url=https://www.science.org/doi/10.1126/science.adg0269 |journal=Science |language=en |volume=380 |issue=6650 |pages=1136–1140 |doi=10.1126/science.adg0269 |pmid=37319198 |bibcode=2023Sci...380.1136V |issn=0036-8075 |access-date=2024-04-23 |archive-date=2024-04-24 |archive-url=https://web.archive.org/web/20240424040546/https://www.science.org/doi/10.1126/science.adg0269 |url-status=live |url-access=subscription }}</ref> Most such objects are rendered invisible in heavily light-polluted skies above major cities. A simple method for estimating the darkness of a location is to look for the [[Milky Way]], which from truly dark skies appears bright enough to cast a shadow.<ref>{{cite APOD |date=23 August 2010 |title=A Milky Way Shadow at Loch Ard Gorge |access-date=2011-12-03}}</ref>

In addition to skyglow, light trespass can impact observations when artificial light directly enters the tube of the telescope and is reflected from non-optical surfaces until it eventually reaches the [[eyepiece]].<ref>{{Cite journal |last=Stone |first=Richard |date=2010-08-27 |title=Astronomers Hope Their Prize Telescope Isn't Blinded by the Light |journal=Science |volume=329 |issue=5995 |page=1002 |doi=10.1126/science.329.5995.1002 |pmid=20798287 |bibcode=2010Sci...329.1002S |issn=0036-8075}}</ref> This direct form of light pollution causes a glow across the [[field of view]], which reduces contrast. Light trespass also makes it hard for a visual observer to become sufficiently adapted to the dark. The usual measures to reduce this glare, if reducing the light directly is not an option, include [[flocking (texture)|flocking]] the telescope tube and accessories to reduce reflection, and putting a light shield (also usable as a [[dew shield]]) on the telescope to reduce light entering from angles other than those near the target. Under these conditions, some astronomers prefer to observe under a black cloth to ensure maximum [[adaptation (eye)|adaptation]] to the dark.

===Increase in atmospheric pollution===

A study presented at the [[American Geophysical Union]] meeting in [[San Francisco]] found that light pollution destroys [[nitrate]] [[Radical (chemistry)|radicals]] thus preventing the normal night time reduction of atmospheric smog produced by fumes emitted from cars and factories.<ref>{{cite news | url=https://www.bbc.co.uk/news/science-environment-11990737 | work=BBC News | title=City lighting 'boosts pollution' | date=2010-12-14 | access-date=2018-06-22 | archive-date=2021-06-03 | archive-url=https://web.archive.org/web/20210603043113/https://www.bbc.co.uk/news/science-environment-11990737 | url-status=live }}</ref><ref>{{cite web | url=http://www.agu.org/cgi-bin/SFgate/SFgate?language=English&verbose=0&listenv=table&application=fm10&convert=&converthl=&refinequery=&formintern=&formextern=&transquery=au%3dstark&_lines=&multiple=0&descriptor=%2fdata%2fepubs%2fwais%2findexes%2ffm10%2ffm10 | title=Nighttime photochemistry: Nitrate radical destruction by anthropogenic light sources }}{{Dead link|date=July 2018 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> The study was presented by Harald Stark from the [[National Oceanic and Atmospheric Administration]].

===Reduction of natural sky polarization===

[[File:Effect of light pollution on sky polarization.jpg|thumb|Light pollution is mostly unpolarized, and its addition to moonlight results in a decreased polarization signal.]]

In the night, the polarization of the moonlit sky is strongly reduced in the presence of [[Urban area|urban]] light pollution, because scattered urban light is generally not strongly polarized, especially in urban areas.<ref>{{cite journal|last1=Kyba|first1=C. C. M.|author2=Ruhtz, T.|author3=Fischer, J.|author4=Hölker, F.|title=Lunar skylight polarization signal polluted by urban lighting|journal=Journal of Geophysical Research|date=17 December 2011|volume=116|issue=D24|pages=D24106|doi=10.1029/2011JD016698|bibcode=2011JGRD..11624106K|url=http://www.slideshare.net/sacani/lunar-skylight-polarization-signal-polluted-by-urban-lighting|access-date=2014-02-21|doi-access=free|archive-date=2017-02-02|archive-url=https://web.archive.org/web/20170202050536/http://www.slideshare.net/sacani/lunar-skylight-polarization-signal-polluted-by-urban-lighting|url-status=live}}</ref> When the moon is not up, it is possible for the sky to become polarized to some degree, particularly in the case of strongly non-uniform light sources.<ref>{{Cite journal |last1=Kocifaj |first1=M |last2=Markoš |first2=P |last3=Kundracik |first3=F |last4=Barentine |first4=J C |last5=Wallner |first5=S |date=2024-07-27 |title=Night sky polarization model for a cloud-free atmosphere illuminated by ground-based light sources |url=https://academic.oup.com/mnras/article/532/4/4864/7726731 |journal=Monthly Notices of the Royal Astronomical Society |language=en |volume=532 |issue=4 |pages=4864–4875 |doi=10.1093/mnras/stae1803 |doi-access=free |issn=0035-8711}}</ref> The polarization pattern of the sky cannot be directly perceived by the human visual system, but is used by some animals for orientation and navigation.<ref>{{Cite journal |last1=Dacke |first1=Marie |last2=Nilsson |first2=Dan-Eric |last3=Scholtz |first3=Clarke H. |last4=Byrne |first4=Marcus |last5=Warrant |first5=Eric J. |date=2003-07-03 |title=Insect orientation to polarized moonlight |url=https://www.nature.com/articles/424033a |journal=Nature |language=en |volume=424 |issue=6944 |page=33 |doi=10.1038/424033a |pmid=12840748 |issn=0028-0836}}</ref><ref>{{Cite journal |last1=Foster |first1=James J. |last2=Tocco |first2=Claudia |last3=Smolka |first3=Jochen |last4=Khaldy |first4=Lana |last5=Baird |first5=Emily |last6=Byrne |first6=Marcus J. |last7=Nilsson |first7=Dan-Eric |last8=Dacke |first8=Marie |date=2021 |title=Light pollution forces a change in dung beetle orientation behavior |journal=Current Biology |language=en |volume=31 |issue=17 |pages=3935–3942.e3 |doi=10.1016/j.cub.2021.06.038|pmid=34329592 |bibcode=2021CBio...31E3935F |doi-access=free }}</ref>

===Economic relation===
It is not uncommon to find 24-hour business, such as gas stations, convenience stores, and pharmacies. Hospitals and other healthcare facilities must be staffed 24 hours per day, seven days per week. With the rise of Amazon, many factories and shipping companies now operate [[24/7 service|24x7]] shifts to keep up with the demand of the new global consumer. These industries all require light, both inside and outside their facilities to ensure the safety of their workers as they move about their jobs and when the enter and depart the facilities. As a result, "40% of the United States and almost 20% of the European Union population has lost the ability to view the night sky…in other words, it is as if they never really experience nighttime."<ref name="Cinzano-2001" />

With a focus on shift work and the continued need for 24-hour operations of specific sectors of the economy, researchers are looking at the impact of light pollution on this group of workers. In 2007 the International Agency for Research on Cancer (IARC) sought to bring notice to the risk from shift work as a probable risk for developing cancers.<ref>{{Cite journal |last1=Erren |first1=Thomas C. |last2=Falaturi |first2=Puran |last3=Morfeld |first3=Peter |last4=Knauth |first4=Peter |last5=Reiter |first5=Russel J. |last6=Piekarski |first6=Claus |date=24 September 2010 |title=Shift Work and Cancer |journal=Deutsches Ärzteblatt International |volume=107 |issue=38 |pages=657–662 |doi=10.3238/arztebl.2010.0657 |issn=1866-0452 |pmc=2954516 |pmid=20953253}}</ref> This move was the result of numerous studies that found increased risks of cancers in groups of shift workers. The 1998 Nurses Health Study found a link between breast cancer and nurses who had worked rotating night shifts in their young adult life.<ref>{{Cite journal |last1=Wegrzyn |first1=Lani R. |last2=Tamimi |first2=Rulla M. |last3=Rosner |first3=Bernard A. |last4=Brown |first4=Susan B. |last5=Stevens |first5=Richard G. |last6=Eliassen |first6=A. Heather |last7=Laden |first7=Francine |last8=Willett |first8=Walter C. |last9=Hankinson |first9=Susan E. |last10=Schernhammer |first10=Eva S. |date=2017-09-01 |title=Rotating Night-Shift Work and the Risk of Breast Cancer in the Nurses' Health Studies |url=https://academic.oup.com/aje/article/186/5/532/3852271 |journal=American Journal of Epidemiology |language=en |volume=186 |issue=5 |pages=532–540 |doi=10.1093/aje/kwx140 |issn=0002-9262 |pmc=5856106 |pmid=28541391 |access-date=2024-04-17 |archive-date=2024-04-14 |archive-url=https://web.archive.org/web/20240414043441/https://academic.oup.com/aje/article/186/5/532/3852271 |url-status=live }}</ref> However, it is not possible to halt shift work in these industries. Hospitals must be staffed around the clock.

Research suggests that, like other environmental issues, light pollution is primarily a problem caused by [[Developed country|industrialized nations]]. Numerous economic indicators have been examined to get a better sense of where light pollution was occurring around the globe.<ref name="Gallaway-2010">{{Cite journal |last1=Gallaway |first1=Terrel |last2=Olsen |first2=Reed N. |last3=Mitchell |first3=David M. |date=15 January 2010 |title=The economics of global light pollution |journal=Ecological Economics |volume=69 |issue=3 |pages=658–665 |doi=10.1016/j.ecolecon.2009.10.003 |issn=0921-8009}}</ref> Countries with [[Road surface|paved roads]], an indicator of developed infrastructure, often had increased light pollution.<ref name="Gallaway-2010" /> Similarly, countries with a high rate of resource extraction also have high rates of light pollution. Also those with the highest [[Gross domestic product|GDP]] and high surface area described as urban and suburban also had the highest rates of light pollution.<ref name="Gallaway-2010" />

China is an emerging leader in industrial and economic growth. A recent study of light pollution using the Defense Meteorological Satellite Program Operational Linescan System (DMSL/OLS) found that light pollution is increasing over the eastern coastal cities but decreasing over the industrial and mineral extraction cities.<ref name="Han-2014"/> Specifically, urban areas around the Yangtze River delta, Pearl River delta, and Beijing-Tianjin area are specific light pollution areas of concern.<ref name="Han-2014" /> Examining China as a whole, it was found that light pollution in the East and North was much higher than the West. This is consistent with major industrial factories located in the East and North while resource extraction dominates the West.<ref name="Han-2014" />

In 2009, following the United Nations declaration of ''The Year of Astronomy,'' researchers urged a better understanding of artificial light and the role it plays in social, economic, and environmental issues.<ref name="Hölker-2010">{{Cite journal |last1=Hölker |first1=Franz |last2=Moss |first2=Timothy |last3=Griefahn |first3=Barbara |last4=Kloas |first4=Werner |last5=Voigt |first5=Christian C. |last6=Henckel |first6=Dietrich |last7=Hänel |first7=Andreas |last8=Kappeler |first8=Peter M. |last9=Völker |first9=Stephan |last10=Schwope |first10=Axel |last11=Franke |first11=Steffen |last12=Uhrlandt |first12=Dirk |last13=Fischer |first13=Jürgen |last14=Klenke |first14=Reinhard |last15=Wolter |first15=Christian |date=2010 |title=The Dark Side of Light: A Transdisciplinary Research Agenda for Light Pollution Policy |journal=Ecology and Society |volume=15 |issue=4 |article-number=art13 |doi=10.5751/es-03685-150413 |issn=1708-3087}}</ref> Continued unfettered use of artificial light in urban and rural areas would cause a global shift with unpredictable outcomes. Focusing on the economic impact of increased energy consumption in light bulbs, or the move to energy efficiency of lighting, is not enough. Rather, the broader focus should be on the socio-economic, ecologic, and physiologic impacts of light pollution.<ref name="Hölker-2010" />

Humans require some artificial night light for shift work, manufacturing, street safety, and nighttime driving and research has shown that artificial light disrupts the lives of animals. However, recent studies suggest that we may be able to find a happy medium. A 2021 article examined seasonal light changes and its effect on all animals, but specifically mollusks.<ref name="Hussein-2020">{{Cite journal |last1=Hussein |first1=Ahmed A. A. |last2=Bloem |first2=Erik |last3=Fodor |first3=István |last4=Baz |first4=El-Sayed |last5=Tadros |first5=Menerva M. |last6=Soliman |first6=Maha F. M. |last7=El-Shenawy |first7=Nahla S. |last8=Koene |first8=Joris M. |date=2020-12-19 |title=Slowly seeing the light: an integrative review on ecological light pollution as a potential threat for mollusks |journal=Environmental Science and Pollution Research |volume=28 |issue=5 |pages=5036–5048 |doi=10.1007/s11356-020-11824-7 |pmid=33341922 |pmc=7838132 |issn=0944-1344}}</ref> The article claims that previous light research primarily focuses on length of exposure to light.<ref name="Hussein-2020" /> However, further research should attempt to determine the safest amount of light exposure, in terms of duration and intensity, that would be most desirable for both humans and animals.<ref name="Hussein-2020" /> With the development on this data, possible safety limits could be applied for light levels.<ref name="Hussein-2020" /> Ideally, the light level would maintain human benefits, while also decreasing or fully removing the negative impacts on animals.

=== Noctalgia ===
Noctalgia is the feeling of loss of access to seeing a starry [[night sky]]. This also includes the feeling of "sky grief", where people no longer have the ability to look at the stars, something that has been done for most of human existence.<ref>{{Cite magazine |last1=Sutter |first1=Paul |author2=Space.com |date=2023-09-26 |title=The Loss of Dark Skies Is So Painful, Astronomers Coined a New Term for It |url=https://www.scientificamerican.com/article/the-loss-of-dark-skies-is-so-painful-astronomers-coined-a-new-term-for-it1/ |access-date=2023-10-20 |magazine=[[Scientific American]] |language=en |archive-date=2023-10-23 |archive-url=https://web.archive.org/web/20231023194331/https://www.scientificamerican.com/article/the-loss-of-dark-skies-is-so-painful-astronomers-coined-a-new-term-for-it1/ |url-status=live }}</ref> The phenomenon also includes the grief over not being able to have the sense of awe and wonder that humans often experience when stargazing.

Coined by Aprana Venkatesan of the [[University of San Francisco]] and John Barentine, an astronomer, the term first appeared in August 2023 as a response to an article on the effects of light pollution published in the journal [[Science (journal)|Science]].<ref name="Noctalgia eLetter">{{Cite journal |last1=Venkatesan |first1=Aprana |last2=Barentine |first2=John |date=2023-08-27 |title=Noctalgia (sky grief): Our Brightening Night Skies and Loss of Environment for Astronomy and Sky Traditions |url=https://www.science.org/doi/10.1126/science.adi4552 |access-date=2023-10-22 |journal=Science ELetters |volume=380 |issue=6650 |pages=1116–1117 |doi=10.1126/science.adi4552 |pmid=37319220 |language=en |arxiv=2308.14685 |bibcode=2023Sci...380.1116S |archive-date=2023-10-22 |archive-url=https://web.archive.org/web/20231022060452/https://www.science.org/doi/10.1126/science.adi4552 |url-status=live }}<!-- As of 2023-10-22, scroll down to the eLetters section for the source in question; no direct URL or anchor found other than the arXiv one. --></ref> Venkatesan and Barentine presented an all-encompassing definition that includes the loss of cultural identity and practices, such as [[storytelling]] and [[stargazing]], as well as ancient knowledge such as [[celestial navigation]].<ref>{{Cite web |date=2023-10-04 |title=Sky grief |website=Borneo Bulletin Online |agency=[[Agence France-Presse]] |url=https://borneobulletin.com.bn/sky-grief/ |access-date=2023-10-20 |language=en-US |archive-date=2023-10-23 |archive-url=https://web.archive.org/web/20231023194332/https://borneobulletin.com.bn/sky-grief/ |url-status=live }}</ref> The authors argued that the night sky deserves a global protection scheme as an important part of the global heritage.<ref name="Noctalgia eLetter" />

==Remediation==

[[Energy conservation]] advocates contend that light pollution must be addressed by changing the [[Habituation|habit]]s of society,<ref>{{cite journal |last1=Ramírez |first1=Francisco |last2=Cordón |first2=Yago |last3=García |first3=Diego |last4=Rodríguez |first4=Airam |last5=Coll |first5=Marta |last6=Davis |first6=Lloyd S. |last7=Chiaradia |first7=Andre |last8=Carrasco |first8=Josep L. |date=15 August 2023 |title=Large-scale human celebrations increase global light pollution |journal=People and Nature |volume=5 |issue=5 |pages=1552–1560 |bibcode=2023PeoNa...5.1552R |doi=10.1002/pan3.10520 |s2cid=261041024 |doi-access=free |hdl-access=free |hdl=10261/334494}}</ref> so that lighting is used more [[lighting efficiency|efficiently]], with less waste and less creation of unwanted or unneeded illumination.<ref>{{Cite journal |last1=de Vries |first1=Peter |last2=Aarts |first2=Henk |last3=Midden |first3=Cees J. H. |date=2011-01-12 |title=Changing Simple Energy-Related Consumer Behaviors |journal=Environment and Behavior |volume=43 |issue=5 |pages=612–633 |doi=10.1177/0013916510369630 |bibcode=2011EnvBe..43..612D |issn=0013-9165}}</ref> Several industry groups<ref>{{Cite web |title=Light Pollution Education and Advocacy |url=https://www.nightskyresourcecenter.org/light-pollution-educational-and-advocacy |access-date=2024-04-21 |website=Night Sky Resource Center |language=en-US |archive-date=2024-04-23 |archive-url=https://web.archive.org/web/20240423233012/https://www.nightskyresourcecenter.org/light-pollution-educational-and-advocacy |url-status=live }}</ref> also recognize light pollution as an important issue. For example, the Institution of Lighting Engineers in the United Kingdom provides its members with information about light pollution, the problems it causes, and how to reduce its impact.<ref>[https://web.archive.org/web/20070212032719/http://www.ile.org.uk/index.php?page=pollution Light Nuisance]. Institution of Light Engineers</ref> Research in 2017 suggested that [[Efficient energy use|energy efficiency]] may not be enough to reduce the light pollution because of the [[Rebound effect (conservation)|rebound effect]].<ref>{{cite journal |last1=Kyba |first1=Christopher C. M. |last2=Kuester |first2=Theres |last3=Sánchez de Miguel |first3=Alejandro |last4=Baugh |first4=Kimberly |last5=Jechow |first5=Andreas |last6=Hölker |first6=Franz |last7=Bennie |first7=Jonathan |last8=Elvidge |first8=Christopher D. |last9=Gaston |first9=Kevin J. |last10=Guanter |first10=Luis |date=22 November 2017 |title=Artificially lit surface of Earth at night increasing in radiance and extent |url=https://ore.exeter.ac.uk/repository/handle/10871/30020 |journal=Science Advances |volume=3 |issue=11 |article-number=e1701528 |bibcode=2017SciA....3E1528K |doi=10.1126/sciadv.1701528 |pmc=5699900 |pmid=29181445 |access-date=22 February 2018 |archive-date=24 November 2020 |archive-url=https://web.archive.org/web/20201124101647/https://ore.exeter.ac.uk/repository/handle/10871/30020 |url-status=live }}</ref>

Light levels can be quantified by field measurement or [[mathematical model]]ing, the results of which are typically rendered in [[isophote]] maps or light [[contour line|contour map]]s. To deal with light pollution, authorities have taken a variety of measures depending on the interests, beliefs, and understandings of the society involved.<ref name="Pothukuchi 2021 155–169">{{Cite journal |last=Pothukuchi |first=Kameshwari |date=2021 |title=City Light or Star Bright: A Review of Urban Light Pollution, Impacts, and Planning Implications |url=http://journals.sagepub.com/doi/10.1177/0885412220986421 |journal=Journal of Planning Literature |language=en |volume=36 |issue=2 |pages=155–169 |doi=10.1177/0885412220986421 |issn=0885-4122 |access-date=2024-04-09 |archive-date=2024-04-09 |archive-url=https://web.archive.org/web/20240409150918/https://journals.sagepub.com/doi/10.1177/0885412220986421 |url-status=live |url-access=subscription }}</ref> These measures range from doing nothing at all to implementing strict laws and regulations specifying how lights may be installed and used.

==Reduction==

<!-- [[Light pollution reduction]] redirects here. -->Reducing light pollution implies many things, such as reducing sky glow, reducing glare, reducing light trespass, and reducing clutter. The method for best reducing light pollution, therefore, depends on exactly what the problem is in any given instance. Possible solutions include:
* Utilizing light sources of minimum intensity necessary to accomplish the light's purpose.
* Turning lights off using a timer or [[occupancy sensor]] or manually when not needed. For example, wind turbines have blinking lights that warn aircraft, to prevent collisions.<ref name="Lewis-2023"/> Residents living near [[Wind farm|windfarms]], especially those in rural areas, have complained that the blinking lights are a bothersome form of light pollution.<ref name="Lewis-2023"/> A light mitigation approach involves Aircraft Detection Lighting Systems (ADLSs) by which the lights are turned on, only when the ADLS's [[radar]] detects aircraft within thresholds of altitude and distance.<ref name="Lewis-2023">{{cite news |last1=Lewis |first1=Michelle |title=A new wind farm in Kansas trailblazes with light-mitigating technology |url=https://electrek.co/2023/09/29/a-new-wind-farm-in-kansas-trailblazes-with-light-mitigating-technology/ |publisher=Electrek |date=29 September 2023 |archive-url=https://web.archive.org/web/20230929161033/https://electrek.co/2023/09/29/a-new-wind-farm-in-kansas-trailblazes-with-light-mitigating-technology/ |archive-date=29 September 2023 |url-status=live }}</ref>
* Improving lighting fixtures, so they direct their light more accurately towards where it is needed, and with fewer side effects.
* Adjusting the ''type'' of lights used, so the light waves emitted are those that are less likely to cause severe light pollution problems. [[Mercury-vapor lamp|Mercury]], [[Metal-halide lamp|metal halide]] and above all first generation of blue-light [[Light-emitting diode|LED]] road luminaires are much more polluting than [[Sodium-vapor lamp|sodium lamps]]: Earth's atmosphere scatters and transmits blue light better than yellow or red light. It is a common experience observing "glare" and "fog" around and below LED road luminaires as soon as air humidity increases, while orange sodium lamp luminaires are less prone to showing this phenomenon.
* Evaluating existing lighting plans, and re-designing some or all the plans depending on whether existing light is actually needed.

===Improving lighting fixtures===

The use of ''full cutoff'' lighting fixtures, as much as possible, is advocated by most campaigners for the reduction of light pollution. It is also commonly recommended that lights be spaced appropriately for maximum efficiency, and that number of luminaires being used as well as the wattage of each luminaire match the needs of the particular application (based on local lighting design standards).

Full cutoff fixtures first became available in 1959 with the introduction of [[General Electric]]'s M100 fixture.<ref name="AM-Feb2009-57">{{cite journal|last=Bakich|first=M.E.|date=February 2009|title=Can we win the war against light pollution|journal=[[Astronomy Magazine]]|page=57|issn=0091-6358}}</ref>

A full cutoff fixture, when correctly installed, reduces the chance for light to escape above the plane of the horizontal. Light released above the horizontal may sometimes be lighting an intended target, but often serves no purpose. When it enters into the atmosphere, light contributes to sky glow. Some governments and organizations are now considering, or have already implemented, full cutoff fixtures in street lamps and stadium lighting.

The use of full cutoff fixtures helps to reduce sky glow by preventing light from escaping above the horizontal. Full cutoff typically reduces the visibility of the lamp and reflector within a luminaire, so the effects of glare are also reduced. Campaigners also commonly argue that full cutoff fixtures are more efficient than other fixtures, since light that would otherwise have escaped into the atmosphere may instead be directed towards the ground. However, full cutoff fixtures may also trap more light in the fixture than other types of luminaires, corresponding to lower luminaire efficiency, suggesting a re-design of some luminaires may be necessary.

The use of full cutoff fixtures can allow for lower wattage lamps to be used in the fixtures, producing the same or sometimes a better effect, due to being more carefully controlled. In every lighting system, some sky glow also results from light reflected from the ground. This reflection can be reduced, however, by being careful to use only the lowest wattage necessary for the lamp, and setting spacing between lights appropriately.<ref>[http://www.rpi.edu/dept/lrc/nystreet/ NYSERDA How-to Guide to Effective Energy-Efficient Street Lighting for Planners and Engineers.] {{Webarchive|url=https://web.archive.org/web/20110102010555/http://www.rpi.edu/dept/lrc/nystreet/ |date=2011-01-02 }} NYSERDA-Planners (October 2002). New York State Energy Research and Development Authority.</ref> Assuring luminaire setback is greater than 90° from highly reflective surfaces also diminishes reflectance.

A common criticism of full cutoff lighting fixtures is that they are sometimes not as aesthetically pleasing to look at. This is most likely because historically there has not been a large market specifically for full cutoff fixtures, and because people typically like to see the source of illumination. Due to the specificity with their direction of light, full cutoff fixtures sometimes also require expertise to install for maximum effect.

The effectiveness of using full cutoff roadway lights to combat light pollution has also been called into question. According to design investigations, luminaires with full cutoff distributions (as opposed to ''cutoff'' or ''semi cutoff'', compared here)<ref>{{cite web |url=http://www.eskimo.com/~jrterry/optics.html |title=Optics for Streetlights |publisher=Eskimo.com |access-date=2010-09-04 |archive-url=https://web.archive.org/web/20100915083231/http://www.eskimo.com/~jrterry/optics.html |archive-date=2010-09-15 }}</ref> have to be closer together to meet the same light level, uniformity and glare requirements specified by the [[Illuminating Engineering Society of North America|IESNA]]. These simulations optimized the height and spacing of the lights while constraining the overall design to meet the IESNA requirements, and then compared total uplight and energy consumption of different luminaire designs and powers. Cutoff designs performed better than full cutoff designs, and semi-cutoff performed better than either cutoff or full cutoff. This indicates that, in roadway installations, over-illumination or poor uniformity produced by full cutoff fixtures may be more detrimental than direct uplight created by fewer cutoff or semi-cutoff fixtures. Therefore, the overall performance of existing systems could be improved more by reducing the number of luminaires than by switching to full cutoff designs.

However, using the definition of "light pollution" from some Italian regional bills (i.e., "every irradiance of artificial light outside competence areas and particularly upward the sky") only full cutoff design prevents light pollution. The Italian [[Lombardy]] region, where only full cutoff design is allowed (Lombardy act no. 17/2000, promoted by [[CieloBuio|Cielobuio-coordination for the protection of the night sky]]), in 2007 had the lowest per capita energy consumption for public lighting in Italy. The same legislation also imposes a minimum distance between street lamps of about four times their height, so full cut-off street lamps are the best solution to reduce both light pollution and electrical power usage.<gallery mode="packed">
File:LED Droplight.JPG|alt=This kind of LED droplight could reduce unnecessary light pollution in building interiors.|This kind of LED droplight could reduce unnecessary light pollution in building interiors.
File:Flat-lens cobra luminaire.jpg|alt=A flat-lens cobra luminaire, which is a full-cutoff fixture, is very effective in reducing light pollution. It ensures that light is directed only below the horizontal, which means less light is wasted by directing it outwards and upwards.|A ''flat-lens cobra luminaire'', which is a full-cutoff fixture, is very effective in reducing light pollution. It ensures that light is directed only below the horizontal, which means less light is wasted by directing it outwards and upwards.
File:Drop-lens cobra luminaire.jpg|alt=This drop-lens cobra luminaire allows light to escape sideways and upwards, where it may cause problems.|This ''drop-lens cobra luminaire'' allows light to escape sideways and upwards, where it may cause problems.

File:110101 LightPollution Italian Regional bills specs.jpg|alt=The majority of Italian regions require "zero upward light", which usually implies the use of overall full cut-off lamps for new luminaires, but violations are common.|The majority of Italian regions require "zero upward light", which usually implies the use of overall full cut-off lamps for new luminaires, but violations are common.
</gallery>

===Adjusting types of light sources===

Several different types of light sources exist, each having a variety of properties that determine their appropriateness for different tasks. Particularly notable characteristics are efficiency and spectral power distribution. It is often the case that inappropriate light sources have been selected for a task, either due to ignorance or because more appropriate lighting technology was unavailable at the time of installation. Therefore, poorly chosen light sources often contribute unnecessarily to light pollution and energy waste. By updating light sources appropriately, it is often possible to reduce energy use and pollutive effects while simultaneously improving efficiency and visibility.

Some types of light sources are listed in order of energy efficiency in the table below (figures are approximate maintained values), and include their visual skyglow impact, relative to LPS lighting.<ref>{{cite journal|last1=Luginbuhl|first1=C.|title=The impact of light source spectral power distribution on sky glow|journal=Journal of Quantitative Spectroscopy and Radiative Transfer|date=2014|volume=139|pages=21–26|doi=10.1016/j.jqsrt.2013.12.004|bibcode = 2014JQSRT.139...21L |doi-access=free}}</ref><ref>{{cite journal|last1=Aubé|first1=M.|last2=Roby|first2=J.|last3=Kocifaj|first3=M.|title=Evaluating Potential Spectral Impacts of Various Artificial Lights on Melatonin Suppression, Photosynthesis, and Star Visibility|journal=PLOS ONE|date=2013|doi=10.1371/journal.pone.0067798|pmid=23861808|pmc=3702543|volume=8|issue=7|article-number=e67798|bibcode = 2013PLoSO...867798A |author1-link=:fr:Martin Aubé|doi-access=free}}</ref>

{| class="wikitable" style="width:60%;"
|-
!Type of light source
!Color
!Luminous efficiency<br />(in [[lumen (unit)|lumens]] per [[watt]])
!Sky glow impact<br />(relative to LPS)
|-
|[[LED street light]] (white)
| style="background:#fcfcff;"| warm-white to cool-white
|120
|4–8
|-
|[[Sodium vapor lamp#Low-pressure sodium|Low Pressure Sodium]] (LPS/SOX)
| style="background:#fff04f;"|yellow/amber
|110
|1.0
|-
|[[Sodium vapor lamp#High-pressure sodium|High Pressure Sodium]] (HPS/SON)
| style="background:#ffdc9f;"|pink/amber-white
|90
|2.4
|-
|[[Metal halide lamp|Metal Halide]]
| style="background:#fcfcff;"| warm-white to cool-white
|70
|4–8
|-
|[[Incandescent light bulb|Incandescent]]
| style="background:#ffffdf;"| yellow/white
|8–25
|1.1
|-
|PCA-LED
| style="background:#ffdc9f;"|amber
|
|2.4
|}

Many astronomers request that nearby communities use low-pressure sodium lights or amber [[Aluminium gallium indium phosphide]] LED as much as possible because the principal wavelength emitted is comparably easy to work around or in rare cases filter out.<ref>
{{cite conference
| title = Why Astronomy Needs Low-Pressure Sodium Lighting
| conference = IAU Symposium No. 196—Preserving the Astronomical Sky
| author = Luginbuhl, C.B.
| editor = Cohen, R. J.
| editor2 =Sullivan, W. T.
| issue = 196
| pages = 81–86
| publisher = PASP, San Francisco, USA
| date = 2001}}</ref> The low cost of operating sodium lights is another feature. In 1980, for example, [[San Jose, California]], replaced all street lamps with [[low pressure sodium lamp]]s, whose light is easier for nearby [[Lick Observatory]] to filter out. Similar programs are now in place in [[Arizona]] and [[Hawaii]]. Such yellow light sources also have significantly less visual [[skyglow]] impact,<ref name=fdsc-lslp>{{cite web|last1=Flagstaff Dark Skies Coalition|title=Lamp Spectrum and Light Pollution|url=http://www.flagstaffdarkskies.org/for-wonks/lamp-spectrum-light-pollution/|website=Lamp Spectrum and Light Pollution|access-date=10 April 2016|archive-date=23 September 2018|archive-url=https://web.archive.org/web/20180923164443/http://www.flagstaffdarkskies.org/for-wonks/lamp-spectrum-light-pollution/|url-status=live}}</ref> so reduce visual sky brightness and improve star visibility for everyone.

Disadvantages of low-pressure sodium lighting are that fixtures must usually be larger than competing fixtures, and that color cannot be distinguished, due to its emitting principally a single wavelength of light (see [[security lighting]]). Due to the substantial size of the lamp, particularly in higher wattages such as 135 W and 180 W, control of light emissions from low-pressure sodium luminaires is more difficult. For applications requiring more precise direction of light (such as narrow roadways) the native lamp efficacy advantage of this lamp type is decreased and may be entirely lost compared to [[sodium vapor lamp|high pressure sodium lamps]]. Allegations that this also leads to higher amounts of light pollution from luminaires running these lamps arise principally because of older luminaires with poor shielding, still widely in use in the UK and in some other locations. Modern low-pressure sodium fixtures with better optics and full shielding, and the decreased [[skyglow]] impacts of yellow light preserve the luminous efficacy advantage of low-pressure sodium and result in most cases is less energy consumption and less visible light pollution. Unfortunately, due to continued lack of accurate information,<ref>Section ''4.10 What Types of Lamps Are Used in Outdoor Lighting?'' in [http://www.nofs.navy.mil/about_NOFS/darksky/OLCHB1.14/lc-hb-v1-14.html ''Outdoor Lighting Code Handbook''] {{Webarchive|url=https://web.archive.org/web/20161212231714/http://www.nofs.navy.mil/about_NOFS/darksky/OLCHB1.14/lc-hb-v1-14.html |date=2016-12-12 }}. International Dark-Sky Association (2000)</ref> many lighting professionals continue to disparage low-pressure sodium, contributing to its decreased acceptance and specification in lighting standards and therefore its use. According to Narisada and Schrueder (2004), another disadvantage of low-pressure sodium lamps is that some research has found that many people find the characteristic yellow light to be less pleasing aesthetically, although they caution that this research isn't thorough enough to draw conclusions from.<ref>{{cite book |last1=Narisada |first1=Kohei |last2=Schreuder |first2=Duco |title=Light Pollution Handbook |date=2004 |publisher=Springer Science & Business Media |isbn=978-1-4020-2665-2 |page=605 |url=https://books.google.com/books?id=61B_RV3EdIcC&pg=PA605 |language=en |access-date=2023-03-19 |archive-date=2023-09-18 |archive-url=https://web.archive.org/web/20230918112521/https://books.google.com/books?id=61B_RV3EdIcC&pg=PA605 |url-status=live }} "When, however, people were asked whether they liked the lighting, the general opinion was that the low pressure sodium lighting was "ugly" or "eerie". The size of the study does not, however, permit robust conclusions."</ref>

Because of the increased sensitivity of the human eye to blue and green wavelengths when viewing low-luminances (the [[Purkinje effect]]) in the night sky, different sources produce dramatically different amounts of visible [[skyglow]] from the same amount of light sent into the atmosphere. To reduce light pollution caused by blue light, it is necessary to adopt lamps that, while maintaining the same photopic luminous flux, produce minimal scotopic light, and at the same time establish specific restrictions on the emitted wavelengths, particularly by shifting the spectral flux towards the blue side of the scotopic band (below 440&nbsp;nm), to protect star visibility and significantly reduce the impact of artificial night sky glow.<ref name=CIE2001>{{cite book |author=CIE |date=2001 |title=The CIE System of Physical Photometry Draft Standard 010.2/E}}
</ref>

The protected wavelength range, the "P-band", should focus between 440 and 540&nbsp;nm to preserve star visibility and reduce light pollution in wavelengths harmful to scotopic vision, while using lamps that emit less light in this range can help minimize pollution without compromising star visibility and protect health and the environment.<ref name=Falchi2011articolo2>{{cite journal |last1=Falchi |first1=F. |date=2011 |title=Campaign of sky brightness and extinction measurements using a portable CCD camera |journal=Mon. Not. R. Astron. Soc. |volume=412 |issue=1 |pages=33–48|doi=10.1111/j.1365-2966.2010.17845.x |doi-access=free |bibcode=2011MNRAS.412...33F }}
</ref>

===Re-designing lighting plans===

In some cases, evaluation of existing plans has determined that more efficient lighting plans are possible. For instance, light pollution can be reduced by turning off unneeded outdoor lights, and lighting stadiums only when there are people inside. Timers are especially valuable for this purpose. One of the world's first coordinated ''legislative'' efforts to reduce the adverse effect of this pollution on the environment began in [[Flagstaff, Arizona]], in the U.S. There, more than three decades of ordinance development has taken place, with the full support of the population,<ref>[http://www.flagstaffdarkskies.org Flagstaff Dark Skies Coalition] {{Webarchive|url=https://web.archive.org/web/20110118055950/http://www.flagstaffdarkskies.org/ |date=2011-01-18 }}. Flagstaffdarkskies.org (2011-10-24). Retrieved 2011-12-03.</ref> often with government support,<ref>[http://www.coconino.az.gov/comdev.aspx?id=144&terms=lighting Coconino County Lighting and General Codes] {{webarchive|url=https://web.archive.org/web/20110721032922/http://www.coconino.az.gov/comdev.aspx?id=144&terms=lighting |date=2011-07-21 }}. Coconino.az.gov (2008-01-07). Retrieved 2011-12-03.</ref> with community advocates,<ref>[http://docs.darksky.org/AGM/2009/Luginbuhl.ppt Arizona IDA presentation on Lighting issues (PowerPoint)] {{webarchive|url=https://web.archive.org/web/20100706041538/http://docs.darksky.org/AGM/2009/Luginbuhl.ppt |date=2010-07-06 }}. darksky.org.</ref> and with the help of major local observatories,<ref>[http://www.lowell.edu/ Lowell Observatory] {{Webarchive|url=https://web.archive.org/web/20110302233420/http://www.lowell.edu/ |date=2011-03-02 }}. Lowell.edu. Retrieved 2011-12-03.</ref> including the [[United States Naval Observatory Flagstaff Station]]. Each component helps to educate, protect and enforce the imperatives to intelligently reduce detrimental light pollution.

One example of a lighting plan assessment can be seen in a report originally commissioned by the Office of the Deputy Prime Minister in the United Kingdom, and now available through the [[Department for Communities and Local Government]].<ref>{{cite web|title=Towards good practice|work=Lighting in the countryside|url=http://www.communities.gov.uk/publications/planningandbuilding/lighting|access-date = 2008-01-16| archive-url = https://web.archive.org/web/20080108232309/http://www.communities.gov.uk/publications/planningandbuilding/lighting| archive-date = January 8, 2008}} [[Department for Communities and Local Government]], United Kingdom.</ref> The report details a plan to be implemented throughout the UK, for designing lighting schemes in the countryside, with a particular focus on preserving the environment.

In another example, the city of [[Calgary]] has recently replaced most residential street lights with models that are comparably energy efficient.<ref>[http://www.calgary.ca/Transportation/Roads/Pages/Traffic/Traffic-signals-and-streetlights/Envirosmart-streetlight-retrofit/EnviroSmart-streetlight-retrofit.aspx The City of Calgary: Envirosmart Streetlight Retrofit Program] {{webarchive|url=https://web.archive.org/web/20120502014929/http://www.calgary.ca/Transportation/Roads/Pages/Traffic/Traffic-signals-and-streetlights/Envirosmart-streetlight-retrofit/EnviroSmart-streetlight-retrofit.aspx |date=2012-05-02 }}. calgary.ca</ref> The motivation is primarily operation cost and environmental conservation. The costs of installation are expected to be regained through energy savings within six to seven years.

The Swiss Agency for Energy Efficiency (SAFE) uses a concept that promises to be of great use in the diagnosis and design of road lighting, "''consommation électrique spécifique'' (''CES'')", which can be translated into English as "specific electric power consumption (SEC)".<ref>{{cite web |url=http://www.efficace.ch/f/IndexAktuell.html |title=S.A.F.E > Actualité |publisher=Efficace.ch |access-date=2010-09-04 |archive-date=2011-05-12 |archive-url=https://web.archive.org/web/20110512162225/http://www.efficace.ch/f/IndexAktuell.html |url-status=live }}</ref> Thus, based on observed lighting levels in a wide range of Swiss towns, SAFE has defined target values for electric power consumption per metre for roads of various categories. Thus, SAFE currently recommends an SEC of two to three watts per meter for roads less than ten metres wide (four to six for wider roads). Such a measure provides an easily applicable environmental protection constraint on conventional "norms", which usually are based on the recommendations of lighting manufacturing interests, who may not take into account environmental criteria. In view of ongoing progress in lighting technology, target SEC values will need to be periodically revised downwards.
[[File:110213 LED vs Sodium vs Mercury.jpg|thumb|Crossroad in Alessandria, Italy: [[luminaire]]s with [[Mercury Lamp|mercury lamps]] are in the background, [[LED street light]]s in the middle, [[luminaire]]s with [[high pressure sodium lamp]]s are in the foreground.]]

A newer method for predicting and measuring various aspects of light pollution was described in the journal [[Lighting Research & Technology]] (September 2008). Scientists at [[Rensselaer Polytechnic Institute]]'s Lighting Research Center have developed a comprehensive method called Outdoor Site-Lighting Performance (OSP), which allows users to quantify, and thus optimize, the performance of existing and planned lighting designs and applications to minimize excessive or obtrusive light leaving the boundaries of a property. OSP can be used by lighting engineers immediately, particularly for the investigation of glow and trespass (glare analyses are more complex to perform and current commercial software does not readily allow them), and can help users compare several lighting design alternatives for the same site.<ref>[http://newswise.com/articles/view/544092/ Lighting Research Center Develops Framework for Assessing Light Pollution] {{Webarchive|url=https://web.archive.org/web/20110512173038/http://newswise.com/articles/view/544092/ |date=2011-05-12 }} Newswise. Retrieved 2008-09-08.</ref>

In the effort to reduce light pollution, researchers have developed a "Unified System of Photometry", which is a way to measure how much or what kind of [[street light]]ing is needed. The Unified System of Photometry allows light fixtures to be designed to reduce energy use while maintaining or improving perceptions of visibility, safety, and security.<ref>{{cite journal |doi=10.1191/1365782804li114oa |author=Rea, M. |author2=J.D. Bullough |author3=J.P. Freyssinier |author4=A. Bierman |name-list-style=amp |date=2004 |title=A proposed Unified System of Photometry |journal=Lighting Research and Technology |volume=36 |issue=2 |pages=85–111 |s2cid=14721508 }}{{Dead link|date=July 2018 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> There was a need to create a new system of light measurement at night because the biological way in which the eye's rods and cones process light is different in nighttime conditions versus daytime conditions. Using this new system of photometry, results from recent studies have indicated that replacing traditional, yellowish, [[High pressure sodium|high-pressure sodium]] (HPS) lights with "cool" white light sources, such as induction, [[Fluorescent lamp|fluorescent]], [[Ceramic discharge metal halide lamp|ceramic metal halide]], or [[LED]]s can actually reduce the amount of electric power used for lighting while maintaining or improving visibility in nighttime conditions.<ref>{{cite journal|last1=Rea|first1=M.|last2=Yuan|first2=Z.|last3=Bierman|first3=A.|title=The unified system of photometry applied to remote airfield lighting|journal=Lighting Research and Technology|volume=41|pages=51–70|date=2009|doi=10.1177/1477153508095735|s2cid=111174811}}</ref>

The [[International Commission on Illumination]], also known as the CIE from its French title, la Commission Internationale de l'Eclairage, will soon be releasing its own form of unified photometry for outdoor lighting.

===Dark sky reserves===
{{main|Dark-sky preserve}}

In 2001 International Dark Sky Places Program was founded in order to encourage communities, parks and protected areas around the world to preserve and protect dark sites through responsible lighting policies and public education. As of January 2022, there are 195 certified International Dark Sky Places in the world.<ref>{{Cite web|url=https://www.darksky.org/our-work/conservation/idsp/|title=International Dark Sky Places|access-date=2022-04-18|archive-date=2022-04-20|archive-url=https://web.archive.org/web/20220420170943/https://www.darksky.org/our-work/conservation/idsp/|url-status=live}}</ref> For example, in 2016 [[China]] launched its first dark sky reserve in the [[Tibet Autonomous Region]]'s [[Ngari Prefecture]] which covers an area of 2,500 square kilometers. Such areas are important for astronomical observation.<ref>{{Cite web|url=https://www.chinadaily.com.cn/china/2016-06/21/content_25791823.htm|title=China's first dark sky reserve launched in Tibet[1]- Chinadaily.com.cn|website=www.chinadaily.com.cn|access-date=2022-04-18|archive-date=2022-04-18|archive-url=https://web.archive.org/web/20220418173418/https://www.chinadaily.com.cn/china/2016-06/21/content_25791823.htm|url-status=live}}</ref>

=== Community involvement ===
Increased awareness of the effects of artificial lighting could result in legislation to effectively mitigate it. However, some communities may hold back due to factors such as cultural beliefs; in some cultures around the world, darkness may be associated with [[evil]], whereas light would be associated with progress by contrast.<ref name="Pothukuchi 2021 155–169"/> Furthermore, societal standards have made humans more active during the day time.<ref>{{Cite book |title=Ecological consequences of artificial night lighting |publisher=Island Press |year=2006 |editor-last=Rich |editor-first=Catherine |editor-last2=Longcore |editor-first2=Travis}}</ref> However, more recent studies indicate that public awareness of the issue has increased and that more people are experiencing consequences of excessive artificial lighting.<ref>{{Cite journal |last1=Lyytimäki |first1=Jari |last2=Rinne |first2=Janne |date=2013 |title=Voices for the darkness: online survey on public perceptions on light pollution as an environmental problem |url=http://www.tandfonline.com/doi/abs/10.1080/1943815X.2013.824487 |journal=Journal of Integrative Environmental Sciences |language=en |volume=10 |issue=2 |pages=127–139 |doi=10.1080/1943815X.2013.824487 |bibcode=2013JIES...10..127L |issn=1943-815X |access-date=2024-04-09 |archive-date=2024-04-09 |archive-url=https://web.archive.org/web/20240409150918/https://www.tandfonline.com/doi/abs/10.1080/1943815X.2013.824487 |url-status=live }}</ref> An assessment from 2020 shows an increase in citizen awareness in the late 20th century due to the availability of [[internet]] [[search engine]]s and the ability to engage globally. The assessment discussion suggests that better information accessibility and voting may promote understanding and concern about the issue.<ref>{{Cite journal |last1=Zielińska-Dabkowska |first1=Karolina M. |last2=Xavia |first2=Kyra |last3=Bobkowska |first3=Katarzyna |date=2020 |title=Assessment of Citizens' Actions against Light Pollution with Guidelines for Future Initiatives |journal=Sustainability |language=en |volume=12 |issue=12 |page=4997 |doi=10.3390/su12124997 |doi-access=free |bibcode=2020Sust...12.4997Z |issn=2071-1050 }}</ref>

=== Dark infrastructure ===
{{Main|Dark infrastructure}}

Dark infrastructure is the creation and preservation of networks of natural levels of darkness, in an attempt to mitigate and reduce the adverse effects of artificial light on biodiversity. Implementation includes identifying and preserving existing dark networks as well as reducing artificial light at night.<ref>{{Cite journal |last1=Sordello |first1=Romain |last2=Busson |first2=Samuel |last3=Cornuau |first3=Jérémie H. |last4=Deverchère |first4=Philippe |last5=Faure |first5=Baptiste |last6=Guetté |first6=Adrien |last7=Hölker |first7=Franz |last8=Kerbiriou |first8=Christian |last9=Lengagne |first9=Thierry |last10=Le Viol |first10=Isabelle |last11=Longcore |first11=Travis |last12=Moeschler |first12=Pascal |last13=Ranzoni |first13=Jessica |last14=Ray |first14=Nicolas |last15=Reyjol |first15=Yorick |date=2022-03-01 |title=A plea for a worldwide development of dark infrastructure for biodiversity – Practical examples and ways to go forward |url=https://linkinghub.elsevier.com/retrieve/pii/S0169204621002954 |journal=Landscape and Urban Planning |volume=219 |article-number=104332 |doi=10.1016/j.landurbplan.2021.104332 |bibcode=2022LUrbP.21904332S |issn=0169-2046}}</ref>

== Gallery ==
<gallery>
File:Empire State Building Night.jpg|This time [[Exposure (photography)|exposure]] photo of [[New York City]] at night shows [[skyglow]].
File:Light pollution country versus city.png|A comparison of the view of the [[night sky]] from a small rural town (top) and a [[metropolitan area]] (bottom). Light pollution dramatically reduces the visibility of [[star]]s.
File:Light pollution impact.jpg|Impact of light pollution on a starry night, as seen from a 4200 m altitude on [[Mount Damavand]] in [[Iran]].
File:Tiberias at the evening.jpg|alt=|Impact of LED lighting on skyglow at night, as seen at Tiberias, Israel. Before the move to LED lighting in 2017, there was very little skyglow above the city.
</gallery>

== IUCN report ==
In the 2024 report "The World at Night: Preserving Natural Darkness for Heritage Conservation and Night Sky Appreciation" by the [[International Union for Conservation of Nature]], light pollution is scrutinized for its contribution to energy waste and climate change and its detrimental effects on ecosystems, human sleep patterns, and traditions such as those of the [[Māori people|Māori]] with regard to the [[Pleiades]]. The report proposes targeted mitigation strategies such as educational campaigns, legislative action, the implementation of dark sky-compliant lighting, and the promotion of certification programs to encourage better lighting practices and [[astrotourism]].<ref>{{Cite book |last1=Welch |first1=David |url=https://portals.iucn.org/library/node/51414 |title=The world at night |last2=Dick |first2=Robert |last3=Treviño |first3=Karen |last4=Longcore |first4=Travis |last5=Rich |first5=Catherine |last6=Hearnshaw |first6=John |last7=Ruggles |first7=Clive |last8=Dalton |first8=Adam |last9=Barentine |first9=John |date=2024 |publisher=IUCN |isbn=978-2-8317-2260-3 |language=en |access-date=2024-04-04 |archive-date=2024-04-04 |archive-url=https://web.archive.org/web/20240404202810/https://portals.iucn.org/library/node/51414 |url-status=live }}</ref>

==See also==
* [[Roy Henry Garstang]]
{{columns-list|colwidth=30em|

'''Concepts '''
* [[Dark-sky preserve]]
* [[Environmental hazard]]
* [[Floodlight]]
* [[Flicker vertigo]]
* [[Lighting]]
* [[Photosensitive epilepsy]]
* [[Polarized light pollution]]
* [[Scotobiology]]
'''Events '''
* [[Earth Hour]]
* [[National Dark-Sky Week]]
'''Organisations '''
* [[Commission for Dark Skies]] (CfDS)
* [[International Dark-Sky Association]]
* [[SKYGLOW]]
'''Other pollution '''
* [[Noise pollution]]
'''Geographical locations'''
* [[History of street lighting in the United States]]
* [[Light pollution in Hong Kong]]
'''Literature '''
* [[The End of Night (book)|''The End of Night'' (book)]]
* ''[[Tribute in Light]]''
'''[[Wikiversity]]''' 
* [[wikiversity:Lighting ordinance|Lighting ordinance]]
}}

==References==

{{reflist}}

== Further reading ==

'''Introductory'''

* Save the night in Europe. (2021). [http://www.savethenight.eu/What%20is.html What is light pollution?] {{Webarchive|url=https://web.archive.org/web/20210626174554/http://www.savethenight.eu/What%20is.html |date=2021-06-26 }}.

'''Astronomy'''

* Luginbuhl, C. B., Walker, C. E., and Wainscoat R. J. (2009) [http://www.darkskiesawareness.org/files/PTarticle_Lighting&Astronomy.pdf "Lighting and Astronomy: Light Pollution"] {{Webarchive|url=https://web.archive.org/web/20210609064109/http://www.darkskiesawareness.org/files/PTarticle_Lighting%26Astronomy.pdf |date=2021-06-09 }}.

'''Energy'''

* ASSIST. (2009). [https://www.lrc.rpi.edu/programs/solidstate/assist/pdf/AR-VisualEfficacy-Jan2009.pdf Outdoor Lighting: Visual Efficacy] {{Webarchive|url=https://web.archive.org/web/20210626174010/https://www.lrc.rpi.edu/programs/solidstate/assist/pdf/AR-VisualEfficacy-Jan2009.pdf |date=2021-06-26 }}.
* Crawford, M. (2015). [https://spie.org/news/1015-led-light-pollution?highlight=x2408&ArticleID=x115768&SSO=1 LED light pollution: Can we save energy and save the night?] {{Webarchive|url=https://web.archive.org/web/20210626174603/https://spie.org/news/1015-led-light-pollution?highlight=x2408&ArticleID=x115768&SSO=1 |date=2021-06-26 }}

'''Environment and ecology'''

* Albers, S. and Duriscoe, D. (2001) [http://www.georgewright.org/184albers.pdf Modeling Light Pollution from Population Data and Implications for National Park Service Lands] {{Webarchive|url=https://web.archive.org/web/20101123145149/http://georgewright.org/184albers.pdf |date=2010-11-23 }}.
* TAB. (2019). [https://www.tab-beim-bundestag.de/en/research/u30500.html Light pollution – extent, societal and ecological impacts as well as approaches] {{Webarchive|url=https://web.archive.org/web/20210626174555/https://www.tab-beim-bundestag.de/en/research/u30500.html |date=2021-06-26 }}.

'''General'''

* Alliance for Lighting Information. (2017). [http://www.resodance.com/ali/home.html Alliance for Lighting Information] {{Webarchive|url=https://web.archive.org/web/20101217080555/http://www.resodance.com/ali/home.html |date=2010-12-17 }}.
* Dobrzynski, J. H. (2009). [https://www.judithdobrzynski.com/4677/reclaiming-the-night-sky Reclaiming the nighy sky.] {{Webarchive|url=https://web.archive.org/web/20210702031430/http://www.judithdobrzynski.com/4677/reclaiming-the-night-sky |date=2021-07-02 }}
* Fraknoi, A. (2018). [http://www.fraknoi.com/wp-content/uploads/2018/03/Light-Pollution-Bibliography-2018.pdf Light pollution and dark skies: a research guide] {{Webarchive|url=https://web.archive.org/web/20210311005321/http://www.fraknoi.com/wp-content/uploads/2018/03/Light-Pollution-Bibliography-2018.pdf |date=2021-03-11 }}.
* Lewicki, M. (2005). [https://web.archive.org/web/20110224221610/http://www.fraserf.id.au/astronomy/martin-lewicki/lpgallry.htm Adelaide's Light Pollution – And the Solution].
* Light Pollution UK. (2006). [https://web.archive.org/web/20061030205822/http://www.lightpollution.org.uk/ Is light pollution killing our birds?.]
* Owen, D. (2007). [https://www.newyorker.com/magazine/2007/08/20/the-dark-side-2 The Dark Side: Making war on light pollution.] {{Webarchive|url=https://web.archive.org/web/20210509044813/https://www.newyorker.com/magazine/2007/08/20/the-dark-side-2 |date=2021-05-09 }}

'''Handbooks'''

* British Astronomical Association. (2009). [https://britastro.org/dark-skies/pdfs/HANDBOOKTEXT.pdf Blinded by the Light?. A handbook for campaigners against the misuse of artificial light, victims of light pollution and friends of the terrestrial and celestial natural environments] {{Webarchive|url=https://web.archive.org/web/20210626174019/https://britastro.org/dark-skies/pdfs/HANDBOOKTEXT.pdf |date=2021-06-26 }}.

'''Industrialisation'''

* Schivelbusch, W. (1998). [https://www.worldcat.org/oclc/1108099096 Disenchanted Night: The Industrialization of Light in the Nineteenth Century].

'''Reading lists'''

* Kyba, C. (2012). [http://userpage.fu-berlin.de/~kyba/literature.html Light pollution papers (and books)] {{Webarchive|url=https://web.archive.org/web/20200629005038/http://userpage.fu-berlin.de/~kyba/literature.html |date=2020-06-29 }}.

'''UK'''

* Hillarys. (2021). [https://www.hillarys.co.uk/skyglow/ Skyglow: light pollution & the UK's changing skies.] {{Webarchive|url=https://web.archive.org/web/20210630091931/https://www.hillarys.co.uk/skyglow/ |date=2021-06-30 }}

==External links==

===Campaigns and research organizations===

{{columns-list|colwidth=30em|

'''International '''
* [http://www.darksky.org/ DarkSky International (formerly International Dark-Sky Association)]
* [http://www.princia.org/ Princia]

'''Oceanica'''
* [https://web.archive.org/web/20181226040254/http://www.solis.org.au/ Sydney Outdoor Lighting Improvement Society]

'''Europe '''
* [http://www.britastro.org/dark-skies/ Campaign for Dark Skies] (UK)
* [http://www.celfosc.org/indice.html Spanish Cel Fosc]
* [http://stars4all.eu/ Stars4All] European project to disseminate and research about the problem of light pollution
* [http://www.cost-lonne.eu/ Loss of the Night Network (LONNE)]—European Research Network COST Aktion ES1204
* [http://www.verlustdernacht.de/about-us.html ''Verlust der Nacht—Loss of the Night'']—Interdisciplinary light pollution research project in Germany
* [http://www.lightpollution.it/cinzano/en/index.html European Light pollution—technical articles]
* [http://cegepsherbrooke.qc.ca/~aubema/index.php/Prof/Recherches Cégep de Sherbrooke Light pollution research activities]
* Austria: [http://kuffner-sternwarte.at/ Verein Kuffner Sternwarte] ([http://sternhell.at/ How many stars?])

'''North America '''
* [http://selene-ny.org/ SELENE] (New York)
* [https://web.archive.org/web/20190911120252/http://volt.org/ Virginia Outdoor Lighting Taskforce]
* [http://www.illinoislighting.org Illinois Coalition for Responsible Outdoor Lighting] (U.S.A.)
* [http://stars4all.eu/ Stars4All] European project to disseminate and research about the problem of light pollution
* [http://www.lrc.rpi.edu Rensselaer Polytechnic Institute's Lighting Research Center]
* [http://www.flagstaffdarkskies.org/ Dark Skies Coalition]
* US National Park Service [https://www.nps.gov/orgs/1050/index.htm Natural Sounds and Night Skies Division]

}}

=== Conferences and events ===

* The Urban Wildlands Group (2002) [https://www.urbanwildlands.org/conference.html Ecological Consequences of Artificial Night Lighting: Conference] {{Webarchive|url=https://web.archive.org/web/20210628184856/https://www.urbanwildlands.org/conference.html |date=2021-06-28 }}
* ISTIL (2002). [http://www.inquinamentoluminoso.it/istil/venice/index.html The Venice Meeting - Light Pollution Science and Technology Institute] {{Webarchive|url=https://web.archive.org/web/20051220134616/http://www.inquinamentoluminoso.it/istil/venice/index.html |date=2005-12-20 }}
* NOAO (2009). [http://www.darkskiesawareness.org/ Dark skies awareness: an IYA2009 cornerstone project.] {{Webarchive|url=https://web.archive.org/web/20110410132211/http://www.darkskiesawareness.org/ |date=2011-04-10 }}

=== Interactive materials ===

* [http://www.need-less.org.uk/ Need-Less] {{Webarchive|url=https://web.archive.org/web/20210415140419/http://www.need-less.org.uk/ |date=2021-04-15 }}—Interactive simulations that demonstrate the effects of light pollution
* Night Eart. [https://www.nightearth.com/?@1.280895,94.20627,0.3803712730835922z&data=$bWVsMmQx&lang=en Earth at night] {{Webarchive|url=https://web.archive.org/web/20210701221527/https://www.nightearth.com/?@1.280895,94.20627,0.3803712730835922z&data=$bWVsMmQx&lang=en |date=2021-07-01 }}.
* [https://lightpollutionmap.app/ Light Pollution Map] — Interactive global map visualizing light pollution trends from 2006 to 2024 using SQM and Bortle Scale data.

=== Scientific models ===

* Cool, A. D. (2010). [https://web.archive.org/web/20130818040900/http://www.cool.id.au/astronomy/Light_Pollution/Germany_2010_Walkers_Law_Model.jpg German skyglow for population by postcode according to Walker's law.]

=== Presentations ===

* [https://web.archive.org/web/20110512162224/http://www.cormusa.org/uploads/Lamp_Spectrum_and_Light_Pollution.pdf Technical slide show "Lamp Spectrum and Light Pollution: The Other Side of Light Pollution"]

{{Pollution}}
{{Public health}}
{{Artificial light sources}}
{{Environmental science}}

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[[Category:Pollution]]
[[Category:Light sources]]
[[Category:Lighting]]
[[Category:Observational astronomy]]
[[Category:Visibility]]
[[Category:Urban planning]]
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