View source for Selective yellow

{{Short description|Colour for automotive lamps}}
{{infobox colour
|title=Selective yellow (approximation)
|hex=FFBA00
|spelling=colour
|source=[[CIE 1931 color space|CIECD]]
|isccname=Strong orange yellow}}
[[File:Corning Conaphore y.jpg|thumb|right|200px|One of the first optic headlamp lenses, the [[Corning Incorporated|Corning]] Conaphore made of selective yellow "Noviol" glass.]]

'''Selective yellow''' is a colour for [[automotive lighting|automotive lamps]], particularly [[Headlamp#Light_colour|headlamps]] and other road-illumination lamps, such as fog lamps.<ref>[http://www.unece.org/fileadmin/DAM/trans/doc/2005/wp29gre/TRANS-WP29-GRE-2005-04e.pdf UNECE]</ref> Under [[ECE regulations]], headlamps were formerly permitted to be either [[white]] or selective yellow—in [[France]], selective yellow was mandatory for all vehicles' road-illumination lamps until 1993.

==Colour==
Both the internationalized European ECE Regulation 19<ref>[http://www.unece.org/trans/main/wp29/wp29regs/r019r5e.pdf ECE Regulation 19: Uniform Provisions Concerning the Approval of Power-Driven Vehicle Front Fog Lamps]</ref> and North American SAE standard J583<ref>[http://standards.sae.org/j583_200509 SAE Standard J583: Front Fog Lamp]</ref> permit selective yellow [[automotive lighting#Front fog lights|front fog lamps]]. Meanwhile, ECE Regulation 48 (enforced 08 October 2016) requires new vehicles to be equipped with headlamps emitting white light.<ref>[https://op.europa.eu/en/publication-detail/-/publication/192086c4-870f-11e6-b076-01aa75ed71a1/language-en ECE Regulation 48: Uniform Provisions Concerning the Approval of Vehicles with Regard to the Installation of Lighting and Light-Signalling Devices]</ref> However, selective yellow headlamps remain permitted throughout Europe on vehicles already so equipped, as well as in non-European locales, such as Japan<ref>[http://retail.ihs.com/abstracts/jsa/jis-d-5500.jsp Japanese Industrial Standard JIS D-5500] {{webarchive|url=https://web.archive.org/web/20070815142229/http://retail.ihs.com/abstracts/jsa/jis-d-5500.jsp |date=2007-08-15 }} ''Automobile Parts--Lighting and Light Signaling Devices'' p. 5, sec. 4.4.2, table #4</ref> and New Zealand.<ref>[https://web.archive.org/web/20140831152201/http://vehicleinspection.nzta.govt.nz/virms/in-service-wof-and-cof/general/lighting/headlamps New Zealand Vehicle Inspection Requirement Manual p. 4.1.2]</ref>

The intent of selective yellow is to improve [[Visual perception|vision]] by removing short, [[blue]] to [[Violet (color)|violet]] [[wavelength]]s from the projected light. These wavelengths are difficult for the human visual system to process properly, and they cause perceived dazzle and [[Light pollution#Glare|glare]] effects in [[rain]], [[fog]] and [[snow]].<ref name=Snow>{{cite journal|title=Driving in Snow: Effect of Headlamp Color at Mesopic and Photopic Light Levels|journal=SAE Technical Paper Series|date=2001|first=John|last=Bullough|author2=Mark S. Rea|volume=1|doi=10.4271/2001-01-0320|url=http://www.lightingresearch.org/programs/transportation/pdf/SAE/2001-01-0320.pdf|archive-url=https://web.archive.org/web/20060223111121/http://www.lightingresearch.org/programs/transportation/pdf/SAE/2001-01-0320.pdf|url-status=dead|archive-date=2006-02-23|access-date=2010-01-27}}</ref> Removing the blue-violet portion of a lamp's output to obtain selective yellow light can entail filter losses of around 15%,<ref name=Devaux>{{cite report
  | author = Devaux, P.
  | title = State-of-the-Art Signaling and Lighting
  | chapter = State-of-the-Art-Signaling and Lighting
 | series = SAE Technical Paper Series
 | id=700386
  | publisher = Society of Automotive Engineers
  |year=1970
  | volume = 1
 | doi = 10.4271/700386
}}</ref> though the effect of this reduction is said to be mitigated or countervailed by the increased [[visual acuity]] available with yellow rather than white light in bad weather.<ref name=Snow/> 

A research experiment done in the UK in 1968 using [[tungsten]] (non-halogen) lamps found that visual acuity is about 3% better with selective yellow headlamps than with white ones of equal intensity.<ref name=LR156>{{cite report
| last1       = Christie
| first1      = A.W.
| last2      = Ashwood
| first2     = J.E.
| last3      = Symons
| first3     = R.D.H.
| year       = 1968
| title      = Visual Acuity in Yellow Headlights
| publisher  = UK Ministry of Transport Road Research Laboratory
| id=LR 156
| url        = https://trl.co.uk/sites/default/files/LR156.pdf
|archive-url=https://web.archive.org/web/20180729230449/https://trl.co.uk/sites/default/files/LR156.pdf
|archive-date=2018-07-29
| access-date = 29 July 2018
}}</ref> Research done in the Netherlands in 1976 concluded that yellow and white headlamps are equivalent as regards traffic safety, though yellow light causes less discomfort glare than white light.<ref name=SWOV1976>{{cite report
| year       = 1976
| title      = White or Yellow Light for Vehicle Head-Lamps?
| publisher  = Dutch Institute for Road Safety Research
|id=1976-2E
| url        = https://www.swov.nl/publicatie/white-or-yellow-light-vehicle-head-lamps
| access-date = 29 July 2018
}}</ref> Researchers note that tungsten filament lamps emit only a small amount of the blue light blocked by a selective-yellow filter,<ref name=LR156/> so such filtration makes only a small difference in the characteristics of the light output,<ref name=Snow/> and suggest that headlamps using newer kinds of sources such as metal halide (HID) bulbs may, through filtration, give off less visually distracting light while still having greater light output than halogen ones.<ref name=Snow/>

==Formal definition==

The UNECE Regulations formally define selective yellow in terms of the [[CIE 1931 colour space]] as follows:

{| cellspacing="5"
| Limit towards red
| <math>y \ge 0.138 + 0.580 x</math>
|-
| Limit towards green
| <math>y \le 1.290 x - 0.100</math>
|-
| Limit towards white
| <math>y \ge 0.966 - x</math>
|-
| Limit towards spectral value
| <math>y \le 0.992 - x</math>
|}

For front fog lamps, the limit towards white is extended:

{| cellspacing="5"
| rowspan = "2" | Limit towards white
| <math>y \ge 0.940 - x</math>
|-
| <math>y \ge 0.440</math>
|}

The entirety of the basic selective yellow definition lies outside the [[gamut]] of the [[sRGB]] colour space—such a pure yellow cannot be represented using RGB primaries. The colour swatch above is a desaturated approximation, created by taking the [[centroid]] of the standard selective yellow definition at (0.502, 0.477) and moving it towards the D65 [[white point]], until it meets the sRGB gamut triangle at (0.478, 0.458).

<gallery width="200px" height="200px;">
File:Porsche_911_with_selective_yellow_headlights.jpg|[[Porsche 911]] with selective yellow lights
File:foglights.jpg|Selective yellow [[Automotive lighting#Front fog lights|foglights]]
File:fogson.jpg|The beam produced by selective yellow lights
</gallery>

==References==
{{Reflist}}

== External links ==
{{Commonscat|Selective yellow headlamps}}

{{Shades of yellow|Selective yellow}}

[[Category:Automotive lamps]]
[[Category:Shades of yellow]]