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:
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Selective yellow foglights
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The beam produced by selective yellow lights
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Porsche 911 with selective yellow lights
Read more about this topic: Selective Yellow
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