IESNA Definition: the absolute temperature of a blackbody whose chromaticity
most nearly resembles that of the light source.
The correlated color temperature (CCT) is a specification of the color appearance
of the light emitted by a lamp,
relating its color to the color of light from a reference source when heated
to a particular temperature, measured in degrees Kelvin (K). The CCT rating
for a lamp is a general "warmth" or "coolness" measure of its appearance. However,
opposite to the temperature scale, lamps with a CCT rating below 3200 K are
usually considered "warm"
sources, while those with a CCT above 4000 K are usually considered "cool"
The correlated color temperature (CCT) designation for a light source
gives a good indication of the lamp's general appearance, but does not
give information on its specific
spectral power distribution.
Therefore, two lamps may appear to be the same color, but their effects
on object colors can be quite different. Examples of the CCT of some common
light sources are: