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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.