Color temperature is a characteristic of visible light that has important applications in lighting, photography, videography, publishing, manufacturing, and other fields. The color temperature of a light source is the temperature of an ideal black-body radiator that radiates light of comparable hue to that light source. The temperature is conventionally stated in units of absolute temperature, kelvin (K). Color temperature is related to Planck's law and to Wien's displacement law.
Higher color temperatures (5,000 K or more) are cool (blueish white) colors; lower color temperatures (2,700–3,000 K) are warm (yellowish white through red) colors.
In physics, a black body is an idealized object that absorbs all electromagnetic radiation that falls on it. No electromagnetic radiation passes through it and none is reflected. Because no light (visible electromagnetic radiation) is reflected or transmitted, the object appears black when it is cold. However, a black body emits a temperature-dependent spectrum of light. This thermal radiation from a black body is termed black-body radiation.
So colour temp is the key.
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