Illuminant

An illuminant represents a target spectral power distribution of a theoretical real light source. Different standard light sources/illuminants are available in the software. Custom illuminant files might be used optionally.

Illuminant types

The following illuminant types are distinguished:

• A - incandescent, or tungsten, light

• C - north sky daylight, or average daylight

• D65 - the most commonly-used daylight illuminant; average of noon daylight all over the world

• D50 - horizon light (sunlight at sunrise or sunset)

• D55 - mid-morning or mid-afternoon daylight

• D75 - overcast

• F2, Fcw, CWF, F - cool white fluorescent

• TL4 or TL84 - a custom fluorescent; Phillips TL84 fluorescent lamp found in Marks and Spencer stores in Europe

Custom Illuminants

Custom illuminant types can be defined as well.

CIE standard Illuminants

The following illuminants have been published by the CIE:

CIE standard illuminant A

This is intended to represent typical, domestic, tungsten-filament lighting. Its relative spectral power distribution is that of a Planckian radiator at a temperature of approximately 2 856 K. CIE standard illuminant A should be used in all applications of colorimetry involving the use of incandescent lighting, unless there are specific reasons for using a different illuminant.

CIE standard illuminant D65

This is intended to represent average daylight and has a correlated colour temperature of approximately 6 500 K. CIE standard illuminant D65 should be used in all colorimetric calculations requiring representative daylight, unless there are specific reasons for using a different illuminant. Variations in the relative spectral power distribution of daylight are known to occur, particularly in the ultraviolet spectral region, as a function of season, time of day, and geographic location. However, CIE standard illuminant D65 should be used pending the availability of additional information on these variations.