Selective yellow

Selective yellow is a colour for automotive lamps.^[1] Under ECE regulations, headlamps were formerly permitted to be either white or selective yellow — in France, selective yellow was mandatory until 1993^[1].

Both the internationalised European ECE Regulation 19^[2] and North American SAE standard J583^[3] permit selective yellow front fog lamps. ECE Regulation 48 currently requires new vehicles to be equipped with headlamps emitting white light.^[4] However, selective yellow headlamps remain permitted throughout Europe on vehicles already so equipped, as well as in non-European locales such as Japan^[5] and New Zealand^[6].

The intent of selective yellow is to improve vision by removing shorter, blue wavelengths from the projected light, as these wavelengths are difficult for the human visual system to process properly, as well as causing perceived dazzle effects in rain, fog and snow and problems with glare.^[7][1]

Formal definition

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

Limit towards red
Limit towards green
Limit towards white
Limit towards spectral value

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

Limit towards white

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).

Here are images of a race car equipped with selective yellow headlamps and driving lamps, a set of fog lamps designed to produce selective yellow light, and of the light beam emitted from the same lamps:

References

1. ^ ^{a b c} What is Selective-Yellow Light?
2. ^ ECE Regulation 19: Uniform Provisions Concerning the Approval of Power-Driven Vehicle Front Fog Lamps
3. ^ SAE Standard J583: Front Fog Lamp
4. ^ ECE Regulation 48: Uniform Provisions Concerning the Approval of Vehicles with Regard to the Installation of Lighting and Light-Signalling Devices
5. ^ Japanese Industrial Standard JIS D-5500 Automobile Parts--Lighting and Light Signaling Devices p. 5, sec. 4.4.2, table #4
6. ^ New Zealand Vehicle Inspection Requirement Manual p. 4.1.2
7. ^ Bullough, John; Mark S. Rea (2001). "Driving in Snow: Effect of Headlamp Color at Mesopic and Photopic Light Levels" (PDF). SAE Technical Paper Series. http://www.lightingresearch.org/programs/transportation/pdf/SAE/2001-01-0320.pdf. Retrieved 2010-01-27.