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Selective yellow is a colour for
automotive lamps, particularly
headlamps
A headlamp is a lamp attached to the front of a vehicle to illuminate the road ahead. Headlamps are also often called headlights, but in the most precise usage, ''headlamp'' is the term for the device itself and ''headlight'' is the term for ...
and other road-illumination lamps such as fog lamps. Under
ECE regulations
The World Forum for Harmonization of Vehicle Regulations is a working party (WP.29) of the Inland Transport Committee (ITC) of the United Nations Economic Commission for Europe (UNECE). Its responsibility is to manage the multilateral Agreements ...
, headlamps were formerly permitted to be either
white
White is the lightest color and is achromatic (having no hue). It is the color of objects such as snow, chalk, and milk, and is the opposite of black. White objects fully reflect and scatter all the visible wavelengths of light. White o ...
or selective yellow—in
France
France (), officially the French Republic ( ), is a country primarily located in Western Europe. It also comprises of overseas regions and territories in the Americas and the Atlantic, Pacific and Indian Oceans. Its metropolitan area ...
, selective yellow was mandatory for all vehicles' road-illumination lamps until 1993.
Colour
Both the internationalized European ECE Regulation 19 and North American SAE standard J583 permit selective yellow
front fog lamps. Meanwhile, ECE Regulation 48 (enforced 08 October 2016) requires new vehicles to be equipped with headlamps emitting white light. However, selective yellow headlamps remain permitted throughout Europe on vehicles already so equipped, as well as in non-European locales such as Japan and New Zealand.
New Zealand Vehicle Inspection Requirement Manual p. 4.1.2
/ref>
The intent of selective yellow is to improve vision
Vision, Visions, or The Vision may refer to:
Perception Optical perception
* Visual perception, the sense of sight
* Visual system, the physical mechanism of eyesight
* Computer vision, a field dealing with how computers can be made to gain und ...
by removing short, blue
Blue is one of the three primary colours in the RYB colour model (traditional colour theory), as well as in the RGB (additive) colour model. It lies between violet and cyan on the spectrum of visible light. The eye perceives blue when ...
to violet wavelength
In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats.
It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, t ...
s from the projected light. These wavelengths are difficult for the human visual system to process properly, and they cause perceived dazzle and glare effects in rain
Rain is water droplets that have condensed from atmospheric water vapor and then fall under gravity. Rain is a major component of the water cycle and is responsible for depositing most of the fresh water on the Earth. It provides water ...
, fog and snow
Snow comprises individual ice crystals that grow while suspended in the atmosphere—usually within clouds—and then fall, accumulating on the ground where they undergo further changes.
It consists of frozen crystalline water throughout ...
. Removing the blue-violet portion of a lamp's output to obtain selective yellow light can entail filter losses of around 15%, though the effect of this reduction is said to be mitigated or countervailed by the increased visual acuity
Visual acuity (VA) commonly refers to the clarity of vision, but technically rates an examinee's ability to recognize small details with precision. Visual acuity is dependent on optical and neural factors, i.e. (1) the sharpness of the retinal ...
available with yellow rather than white light in bad weather.[
A research experiment done in the UK in 1968 using ]tungsten
Tungsten, or wolfram, is a chemical element with the symbol W and atomic number 74. Tungsten is a rare metal found naturally on Earth almost exclusively as compounds with other elements. It was identified as a new element in 1781 and first isol ...
(non-halogen) lamps found that visual acuity is about 3% better with selective yellow headlamps than with white ones of equal intensity. 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. Researchers note that tungsten filament lamps emit only a small amount of the blue light blocked by a selective-yellow filter,[ so such filtration makes only a small difference in the characteristics of the light output,][ 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.][
]
Formal definition
The UNECE Regulations formally define selective yellow in terms of the CIE 1931 colour space
The CIE 1931 color spaces are the first defined quantitative links between distributions of wavelengths in the electromagnetic visible spectrum, and physiologically perceived colors in human color vision. The mathematical relationships that defi ...
as follows:
For front fog lamps, the limit towards white is extended:
The entirety of the basic selective yellow definition lies outside the gamut
In color reproduction, including computer graphics and photography, the gamut, or color gamut , is a certain ''complete subset'' of colors. The most common usage refers to the subset of colors which can be accurately represented in a given circ ...
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
In mathematics and physics, the centroid, also known as geometric center or center of figure, of a plane figure or solid figure is the arithmetic mean position of all the points in the surface of the figure. The same definition extends to any ...
of the standard selective yellow definition at (0.502, 0.477) and moving it towards the D65 white point
A white point (often referred to as reference white or target white in technical documents) is a set of tristimulus values or chromaticity coordinates that serve to define the color "white" in image capture, encoding, or reproduction. Depending ...
, until it meets the sRGB gamut triangle at (0.478, 0.458).
File:Porsche_911_with_selective_yellow_headlights.jpg, Porsche 911 with selective yellow lights
File:foglights.jpg, Selective yellow foglights
File:fogson.jpg, The beam produced by selective yellow lights
References
External links
{{Shades of yellow, Selective yellow
Automotive lamps
Shades of yellow