| Selective yellow (approximation) | |
|---|---|
 Colour coordinates | |
| Hex triplet | #FFBA00 |
| sRGBB (r,g,b) | (255, 186, 0) |
| HSV (h,s,v) | (44°, 100%, 100%) |
| CIELChuv (L,C,h) | (80, 100, 55°) |
| Source | CIECD |
| ISCC–NBS descriptor | Strong orange yellow |
| B: Normalized to [0–255] (byte) | |
Selective yellow is a colour forautomotive lamps, particularlyheadlamps and other road-illumination lamps, such as fog lamps.[1] UnderECE regulations, headlamps were formerly permitted to be eitherwhite or selective yellow—inFrance, selective yellow was mandatory for all vehicles' road-illumination lamps until 1993.
Both the internationalized European ECE Regulation 19[2] and North American SAE standard J583[3] permit selective yellowfront fog lamps. Meanwhile, ECE Regulation 48 (enforced 08 October 2016) 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 improvevision by removing short,blue tovioletwavelengths from the projected light. These wavelengths are difficult for the human visual system to process properly, and they cause perceived dazzle andglare effects inrain,fog andsnow.[7] Removing the blue-violet portion of a lamp's output to obtain selective yellow light can entail filter losses of around 15%,[8] though the effect of this reduction is said to be mitigated or countervailed by the increasedvisual acuity available with yellow rather than white light in bad weather.[7]
A research experiment done in the UK in 1968 usingtungsten (non-halogen) lamps found that visual acuity is about 3% better with selective yellow headlamps than with white ones of equal intensity.[9] 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.[10] Researchers note that tungsten filament lamps emit only a small amount of the blue light blocked by a selective-yellow filter,[9] so such filtration makes only a small difference in the characteristics of the light output,[7] 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.[7]
The UNECE Regulations formally define selective yellow in terms of theCIE 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 thegamut of thesRGB colour space—such a pure yellow cannot be represented using RGB primaries. The colour swatch above is a desaturated approximation, created by taking thecentroid of the standard selective yellow definition at (0.502, 0.477) and moving it towards the D65white point, until it meets the sRGB gamut triangle at (0.478, 0.458).
