Selective yellow

Selective yellow (desaturated approximation)
— Colour coordinates —
Hex triplet		#FFBA00
RGBB	(r, g, b)	(255, 186, 0)
HSV	(h, s, v)	(44°, 100%, 100%)
Source		CIECD
B: Normalized to [0–255] (byte)

One of the first optic headlamp lenses, the Corning Conaphore. Selective yellow "Noviol" glass version shown.

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].

ECE Regulation 48 currently requires headlamps to emit white light. However, selective yellow front fog lamps are still permitted, and some individual European countries still permit selective yellow headlamps. Some countries outside Europe, such as Japan^[2] and New Zealand^[3], also permit selective yellow headlamps.

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.^[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:

Porsche 911 with selective yellow lights

Selective yellow foglights

The beam produced by selective yellow lights

References

1. ^ ^{a b c} What is Selective-Yellow Light?
2. ^ Japanese Industrial Standard JIS D-5500 Automobile Parts--Lighting and Light Signaling Devices p. 5, sec. 4.4.2, table #4
3. ^ New Zealand Vehicle Inspection Requirement Manual p. 4.1.2

• UNECE Regulation No. 37: Uniform Provisions Concerning the Approval of Filament Lamps for Use in Approved Lamp Units on Power-Driven Vehicles and of their Trailers (E/ECE/324-E/ECE/TRANS/505/Rev.1/Add.36/Rev.4)
• UNECE Regulation No. 48: Uniform Provisions Concerning the Approval of Vehicles with Regard to the Installation of Lighting and Light-Signalling Devices (E/ECE/324-E/ECE/TRANS/505/Rev.1/Add.47/Rev.3/Amend.2)