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.
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.
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.