View source for Strobe light

{{short description|Device producing regular flashes of light}}
{{redirect|Strobe}}
{{redirect|Strob|the fungicide class|Strob fungicide}}
{{for-multi|the Red Sebastian song|Strobe Lights|the Jason Derulo song|Strobelight (song)}}
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[[File:StrobeLight.jpg|thumb|Blue strobe light]]

A '''strobe light''' or '''stroboscopic lamp''', commonly called a '''strobe''', is a device used to produce regular flashes of [[light]]. It is one of a number of devices that can be used as a [[stroboscope]]. The word originated from the [[Ancient Greek]] {{wikt-lang|grc|στρόβος}} (''{{grc-transl|στρόβος}}''), meaning "act of whirling".

A typical commercial strobe light has a flash energy in the region of 10 to 150 [[joule]]s, and discharge times as short as a few milliseconds, often resulting in a flash power of several [[kilowatt]]s. Larger strobe lights can be used in “continuous” mode, producing extremely intense illumination.

The light source is commonly a [[xenon flash lamp]], or ''flashtube'', which has a complex [[spectrum]] and a [[color temperature]] of approximately 5,600 [[kelvin]]s. To obtain colored light, [[color gel|colored gels]] may be used.

== Scientific explanation of flashtubes ==

Strobe lights usually use [[flashtube]]s with energy supplied from a [[capacitor]], an energy storage device much like a battery, but capable of charging and releasing energy much faster.  In a capacitor-based strobe, the capacitor is charged up to around 300 V. Once the capacitor has been charged, to trigger the flash a small amount of power is diverted into a [[trigger transformer]], a small transformer with a high turns ratio. This generates the weak but high-voltage spike required to ionize the xenon gas in a flash tube. An [[Electric arc|arc]] is created inside the tube, which acts as a path for the capacitor to discharge through, allowing the capacitor to quickly release its energy into the arc. The capacitor's energy rapidly heats the xenon gas, creating an extremely bright plasma discharge, which is seen as a flash.

A strobe without a capacitor storage device simply discharges mains voltages across the tube once it's fired. This type of strobe requires no charging time and allows for much quicker flash rates, but drastically reduces the lifetime of the flash tube if powered for significant periods of time. Such strobes require a form of [[current limiting]], without which the flash tube would attempt to draw high currents from the electricity source, potentially tripping [[Circuit breaker|electrical breakers]] or causing [[voltage drop]]s in the power supply line.

The duration of a single flash depends on the particular strobe being used and its settings. Strobes for studio lighting often have a range of power settings. For a given strobe, higher light output corresponds to a longer flash duration. For example, the Flashpoint Rapid 1200 HSS Monolight <ref>{{Cite web|url=https://www.adorama.com/fplfrp1200b.html|title=Flashpoint Rapid 1200 HSS R2 2.4GHz Monolight - Bowens Mount (Godox QT1200IIM) RAPID-1200B|website=Adorama.com|access-date=19 April 2022}}</ref> has a flash duration as long as 5.6 ms (1/180 sec) at its highest output setting, or as short as 68 μs (1/14,814 sec) at its lowest output setting. Strobes with significantly shorter flash durations are commercially available, some with flash durations less than 1 μs. For example, the SPOT strobe by Prism Science Works provides a flash duration of order 0.5 μs<ref>{{Cite web|url=http://prismscience.com/spot_specs.php|title = Prism Science Works|website=Prismscience.com}}</ref>

Some strobes even offer continuous mode of operation whereby the arc is sustained, providing extremely high intensity light, but usually only for small amounts of time to prevent overheating and eventual breakage of the flash tube.

== Applications ==

===Strobe beacons===
[[File:LED-Blaulicht-VW-T5.jpg|thumb|LED Strobe beacon on emergency vehicle]]
A '''strobe [[beacon]]''' is a flashing electric [[Lamp (electrical component)|lamp]] used in a variety of [[Industry (economics)|industries]] as an [[attention]]-getting device, either to warn of possible [[hazard]]s, or to attract potential [[customer]]s. Strobe beacons are similar to rotating beacons, but are more [[Efficient energy use|energy efficient]], and with no moving parts, are more reliable and less likely to break.

'''Gas strobe beacons''' include [[Xenon flash lamp]] and [[halogen]] varieties. Gas strobe beacons consist of a gas-filled [[Tubing (material)|tube]] surrounded by a [[lens (optics)|lens]]. When [[electricity]] is applied, the tube flashes and is magnified by the lens, and a [[Circle|360 degree]] light is emitted. The intensity of the light depends on the amount of electricity provided.<ref>{{Cite web |title=Flashing Strobe Beacon Patent |url=https://patents.google.com/patent/US5521595 |website=[[Google Patents]]}} 
</ref><ref>{{Cite web |title=Halogen Strobe Beacon Patent |url=https://patents.google.com/patent/US4626966 |website=[[Google Patents]]}} </ref>

These lenses come in a variant of colors, mainly clear, yellow, amber, red, blue, and green. The lens color can affect the intensity of light.<ref>{{Cite web |title=beacons.pdf |url=http://www.iceweb.com.au/F&g/beacons.pdf |website=iceweb.com.au}} {{Dead link|date=December 2023|fix-attempted=yes}}</ref>

'''[[Light-emitting diode|LED]] strobe beacons''' consist of a base, a LED or group of LEDs, and a cover. A solid state flash controller is located within the base, which allows the LED beacon to operate in a variety of flash patterns.<ref>[https://patents.google.com/patent/US20060132323 LED Strobe Beacon Patent]
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Strobe lights are often used for aircraft anti-collision lighting both on aircraft themselves and also on tall stationary objects, such as television and radio towers. Other applications are in [[alarm system]]s, [[emergency vehicle lighting]], [[theatre|theatrical]] [[stage lighting instrument|lighting]] (most notably to simulate [[lightning]]), and as high-visibility aircraft [[Anti-collision light|collision avoidance lights]].  They are still widely used in law enforcement and other emergency vehicles, though they are slowly being replaced by [[LED]] technology in this application, as they themselves largely replaced [[Halogen lamp|halogen]] lighting.{{Citation needed|date=July 2021}} Strobes are used by [[scuba diver]]s as an emergency signaling device.<ref name=Davies>{{cite journal |author=Davies, D |title=Diver location devices |journal=Journal of the South Pacific Underwater Medicine Society |volume=28 |issue=3 |date=1998 |url=http://archive.rubicon-foundation.org/5968 |access-date=2009-04-02 |archive-date=2009-05-19 |archive-url=https://web.archive.org/web/20090519022556/http://archive.rubicon-foundation.org/5968 |url-status=usurped }}</ref>

=== Stroboscopic effect ===
{{Main|Stroboscopic effect}}
[[Image:Strobe 2.gif|thumb|right|A strobe light flashing at the proper period can appear to freeze or reverse cyclical motion.]]
Special calibrated strobe lights, capable of flashing up to hundreds of times per second, are used in industry to stop the appearance of motion of rotating and other repetitively operating machinery and to measure, or adjust, the rotation speeds or cycle times. Since this stop is only apparent, a marked point on the rotating body will either appear to move backward or forward, or not move, depending on the frequency of the strobe-flash. If the flash occurs equal to the period of rotation (or an even multiple, i.e. 2*π*n/ω, where n is an integer and ω the [[angular frequency]]), the marked point will appear to not move. Any non-integer flash setting will make the mark appear to move forward or backward, e.g. a slight increase of the flash frequency will make the point appear to move backward.

A common use of a strobe flash is to optimize a [[car engine]]'s efficiency at a certain rotational period by directing the strobe-light towards a mark on the [[flywheel]] on the engine's main [[axle]]. The strobe-light tool for such [[ignition timing]] is called a [[timing light]]. Strobe lighting has also been used to see the movements of the vocal cords in slow motion during speech, a procedure known as video-stroboscopy.

=== Other ===
Strobelights are often used to give an illusion of slow motion in [[nightclub]]s and [[rave]]s, and are available for home use for special effects or entertainment.

== History ==
The origin of strobe lighting dates to 1931, when [[Harold Eugene Edgerton|Harold Eugene "Doc" Edgerton]] employed a flashing lamp to make an improved [[stroboscope]] for the study of moving objects, eventually resulting in dramatic [[photography|photographs]] of objects such as bullets in flight.

<blockquote>[[EG&G]] [''now a division of [[URS Corporation|URS]]''] was founded by Harold E. Edgerton, Kenneth J. Germeshausen and Herbert E. Grier in 1947 as Edgerton, Germeshausen and Grier, Inc. and today bears their initials. In 1931, Edgerton and Germeshausen had formed a partnership to study high-speed photographic and stroboscopic techniques and their applications. Grier joined them in 1934, and in 1947, EG&G was incorporated.

During World War II, the government's [[Manhattan Project]] made use of Edgerton's discoveries to photograph atomic explosions; it was a natural evolution that the company would support the [[United States Atomic Energy Commission|Atomic Energy Commission]] in its weapons research and development after the war. This work for the Commission provided the historic foundation to the Company's present-day technology base.<ref>{{Cite web |url=http://www.urscorp.com/EGG_Division/history.php |title=URS Corporation - EG&G - History |access-date=2007-05-07 |archive-date=2007-07-05 |archive-url=https://web.archive.org/web/20070705050732/http://www.urscorp.com/EGG_Division/history.php |url-status=dead }}</ref></blockquote>

Internally triggered ''Strobotrons'' (light-output optimized [[thyratron]]s) were available<ref>{{cite web |url=http://tubedata.milbert.com/sheets/137/s/SN4.pdf |title= Sylvania: ''1D21/SN4 Strobotron'' data sheet|website=Tubedata.milbert.com |access-date=15 June 2013}}</ref> as well as [[Cathode-ray tube#Flood-beam CRT|flood-beam-CRT]]-type, grid-controlled ''Vacuum stroboscopic light sources'' with fast [[phosphor]]s.<ref>{{cite web |url=http://tubedata.milbert.com/sheets/074/c/CL60.pdf |title= Ferranti: ''CL6x Stroboscopic light source'' data sheet|website=Tubedata.milbert.com |access-date=15 June 2013}}</ref>

The strobe light was popularized on the club scene during the 1960s when it was used to reproduce and enhance the effects of [[LSD]] trips. [[Ken Kesey]] used strobe lighting in coordination with the music of the [[Grateful Dead]] during his [[Acid Tests]].  In early 1966, [[Andy Warhol]]'s lights engineer, Danny Williams, pioneered the use of multiple stroboscopes, slides and film projections simultaneously onstage during the 1966 [[Exploding Plastic Inevitable]] shows, and at [[Bill Graham (promoter)|Bill Graham]]'s request, Williams built an enhanced stroboscopic light show to be used at [[Fillmore West]].

== Fechner color ==
Rapid flashing of a stroboscopic light can give the illusion that white light is tinged with color, known as [[Fechner color]]. Within certain ranges, the apparent color can be controlled by the frequency of the flash. Effective stimuli frequencies go from 3 Hz upwards, with optimal frequencies of about 4–6 Hz. The colours are an illusion generated in the mind of the observer and not a real color. The [[Benham's top]] demonstrates the effect.<ref>{{Cite web|last=Benham|first=CE|date=1894|title=The artificial spectrum top|url=https://scholar.google.com/scholar_lookup?hl=en&volume=51&publication_year=1894&pages=200&author=C+E+Benham&title=%E2%80%9CThe+artificial+spectrum+top%E2%80%9D|access-date=2021-07-31|website=scholar.google.com}}</ref><ref>Pilz J, Marre E (1993). "Pattern-induced flicker colors. An ophthalmologic examination method (Article in German)". ''Ophthalmologe''. '''90''' (2): 148–54. [[PMID (identifier)|PMID]] 8490297.</ref><ref>Schramme J (1992). "Changes in pattern induced flicker colors are mediated by the blue/yellow opponent process". ''Vision Research''. '''32''' (11): 2129–34. [[Doi (identifier)|doi]]:10.1016/0042-6989(92)90074-S. [[PMID (identifier)|PMID]] 1304090.</ref><ref>{{Cite book|last=. Krantz|first=John H|url=http://imbs.uci.edu/~kjameson/ECST/Krantz_FechnerColorsAndBehnamTop.pdf|title=Encyclopedia of Color Science and Technology|publisher=Springer Science+Business Media|year=2013|location=New York|doi=10.1007/978-3-642-27851-8_65-2}}</ref>    

== Seizures ==
Sometimes strobe lighting can trigger [[Epileptic seizure|seizures]]. Several public incidents of [[Photosensitive_epilepsy#Public_incidents|photosensitive epilepsy]] have occurred. Studies have shown that the majority of people that are susceptible to the strobing effects can have symptoms, albeit rarely, at 15&nbsp;Hz-70&nbsp;Hz. Other studies have shown epileptic symptoms at the 15&nbsp;Hz rate with over 90 seconds of continuous staring at a strobe light.{{cn|date=January 2025}} 

While no specific legal requirements are known for public usage, relevant safety control measures should be employed to minimize epileptic seizures and potential trips or falls from disturbed vision. Strobe light flash rates should not exceed 4 flashes per second; when multiple strobe lights are used, flashes should be synchronized. Warnings should be posted at venue entryways, e.g., ''“WARNING: Strobe lights are used during this performance”''. Staff, crew, audiences and viewers should be informed prior to any usage of flickering lights or high contrast image changes.<ref>{{cite web |title=Strobe Lighting: Safety Guideline to strobe lighting used as a visual effect for entertainment performances |url=https://www.bbc.co.uk/safety/resources/aztopics/strobe-lighting |website=www.bbc.co.uk |publisher=British Broadcasting Corporation |access-date=16 January 2025 |date=August 18, 2020}}</ref>

The strobe rate of [[Fire alarm system|fire alarms]] in schools, hospitals, stadiums, etc. for any emergency notification should be maintained between 1.0 - 2.0 Hertz as a seizure precaution.<ref name="NFPA-72">{{cite book |title=NFPA 72 National Fire Alarm and Signaling Code® |date=October 1, 2024 |publisher=National Fire Protection Association (NFPA) |location=Quincy, Massachusetts |page=72-131 |edition=2025 |url=https://link.nfpa.org/free-access/publications/72/2025 |access-date=16 January 2025 |chapter=18.5.3- Light, Color, and Pulse Characteristics |isbn=978-1455931521}}</ref>

Most strobe lights on sale to the public are factory-limited to about 10–12&nbsp;Hz (10–12 flashes per second) in their internal [[oscillators]], although externally triggered strobe lights will often flash as frequently as possible.{{cn|date=January 2025}}

==See also==
{{Wiktionary|strobe}}
* [[Electrotachyscope]], an early motion picture system in limited use between 1886 and 1894.
*[[Emergency vehicle lighting]]
*[[Flicker (light)]], the study of  directly visible change in brightness of a light source
*[[Flicker fusion threshold]],   the frequency at which an intermittent light stimulus appears to be completely steady to the average human observer
* [[Tachometer]], an instrument measuring the rotation speed of a [[Axle|shaft]] or disk,
* [[Zoetrope]],  an early device from 1813 that produced the illusion of motion by displaying a sequence of drawings or photographs showing progressive phases of that motion.
*[[Jerkiness]], discontinuity in motion pictures, also called strobing
*[[flash (photography)|Photographic flash]], often also referred to as a strobe light
*[[Wagon-wheel effect]],  an [[optical illusion]] in cinematography  which a [[Spoke|spoked]] [[wheel]] appears to rotate differently from its true rotation
*[[Air-gap flash]], a photographic light source capable of producing sub-microsecond light flashes, allowing for (ultra) [[high-speed photography]] 

==References==
{{Reflist}}

{{commonscat|Strobe light}}
{{Artificial light sources}}

[[Category:Gas discharge lamps]]
[[Category:History of animation]]
[[Category:1938 introductions]]
[[Category:Devices to alter consciousness]]