correlated color temperature
Correlated color temperature (CCT) describes the relative color appearance of a white light source, indicating whether it appears more yellow/gold or more blue, in terms of the range of available shades of white.
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CCT is given in kelvin (the SI unit of absolute temperature) and refers to the appearance of a theoretical blackbody heated to high temperatures. As the blackbody gets hotter, it turns red, orange, yellow, white, and finally blue. The CCT of a light source is the temperature (in K) at which the heated blackbody matches the color of the light source in question.