In science and technology, absolute temperatures and temperature differences are not specified in the generally used unit of degrees Celsius but in kelvin (symbol: K).
The kelvin is also used to indicate the color impression of „white“ light. The spectrum of a thermal radiator (e.g. light bulb, gas flame, and sun) is given by its temperature, and accordingly one also assigns a „color temperature“ to the light of a non-thermal radiator (e.g. LED, fluorescent tube).
If, for example, the color temperature of an LED lamp is given as 3000 K, this means that it produces the same color impression as a thermal radiator with a temperature of 3000 K. This color would be called „warm white“. This color would be called „warm white“, whereby „warm“ in this context is not related to temperature, but to the division of colors into „warm“ (rather reddish) and „cool“ (rather bluish) colors. Thus, high color temperatures stand for rather cold color impressions. Common light sources have color temperatures ranging from below 3,300 K (warm white), 3,300 to 5,300 K (neutral white) to over 5,300 K (daylight white).