D65 D50 TL83 TL84 U30 U35 Fluorescent Tube Light 60cm Length With Different Color Temperature

Fluorescent Light Tube D65 D50 TL83 U30 Different Color Temperature

CIE Standard Illuminant D65 (sometimes written D65[1][2]) is a commonly used standard illuminant defined by the International Commission on Illumination (CIE).[3] It is part of the D series of illuminants that try to portray standard illumination conditions at open-air in different parts of the world.

D65 corresponds roughly to the average midday light in Western Europe / Northern Europe (comprising both direct sunlight and the light diffused by a clear sky), hence it is also called a daylight illuminant. As any standard illuminant is represented as a table of averaged spectrophotometric data, any light source which statistically has the same relative spectral power distribution (SPD) can be considered a D65 light source. There are no actual D65 light sources, only simulators. The quality of a simulator can be assessed with the CIE Metamerism Index.[4][5]

The CIE positions D65 as the standard daylight illuminant:

[D65] is intended to represent average daylight and has a correlated colour temperature of approximately 6500 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.

— ISO 10526:1999/CIE S005/E-1998, CIE Standard Illuminants for Colorimetry