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 t ...

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 chroma). It is the color of objects such as snow, chalk, and milk, and is the opposite of black. White objects fully (or almost fully) reflect and scatter all the visible wa ...

or selective yellow—in

France France, officially the French Republic, is a country located primarily in Western Europe. Overseas France, Its overseas regions and territories include French Guiana in South America, Saint Pierre and Miquelon in the Atlantic Ocean#North Atlan ...

, 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 color model, RYB colour model (traditional colour theory), as well as in the RGB color model, RGB (additive) colour model. It lies between Violet (color), violet and cyan on the optical spe ...

to violet

wavelength In physics and mathematics, wavelength or spatial period of a wave or periodic function is the distance over which the wave's shape repeats. In other words, it is the distance between consecutive corresponding points of the same ''phase (waves ...

s from the projected light. These wavelengths are difficult for the human visual system to process properly, and they cause perceived dazzle and

glare Glare may refer to: * Glare (vision), difficulty seeing in the presence of very bright light * Glaring, a facial expression of squinted eyes and look of contempt * A call collision in telecommunications * GLARE, Glass reinforced aluminium, an ...

effects in

rain Rain is a form of precipitation where water drop (liquid), droplets that have condensation, condensed from Water vapor#In Earth's atmosphere, atmospheric water vapor fall under gravity. Rain is a major component of the water cycle and is res ...

fog Fog is a visible aerosol consisting of tiny water droplets or ice crystals suspended in the air at or near the Earth's surface. Reprint from Fog can be considered a type of low-lying cloud usually resembling stratus and is heavily influenc ...

and

snow Snow consists of 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 througho ...

. 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 visual perception, vision, but technically rates an animal's ability to recognize small details with precision. Visual acuity depends on optical and neural factors. Optical factors of the eye ...

available with yellow rather than white light in bad weather. A research experiment done in the UK in 1968 using

tungsten Tungsten (also called wolfram) is a chemical element; it has symbol W and atomic number 74. It is a metal found naturally on Earth almost exclusively in compounds with other elements. It was identified as a distinct element in 1781 and first ...

(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 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 and colorimetry, a gamut, or color gamut , is a convex set containing the colors that can be accurately represented, i.e. reproduced by an output device (e.g. printer or display) or measured by an input device (e.g. cam ...

of the

sRGB sRGB (standard RGB) is a colorspace, for use on monitors, printers, and the World Wide Web. It was initially proposed by HP and Microsoft in 1996 and became an official standard of the International Electrotechnical Commission (IEC) as IEC 6 ...

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 figure. The same definition extends to any object in n-d ...

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 o ...

, until it meets the sRGB gamut triangle at (0.478, 0.458). File:Porsche_911_with_selective_yellow_headlights.jpg,

Porsche 911 The Porsche 911 model series (pronounced ''Nine Eleven'' or in ) is a family of German two-door, high performance Rear-engine design, rear-engine sports cars, introduced in September 1964 by Porsche, Porsche AG of Stuttgart, Germany. Now in it ...

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