The color temperature of a light source is the temperature of an ideal black-body radiator that radiates light of comparable hue to that of the light source. Color temperature is a characteristic of visible light that has important applications in lighting, photography, videography, publishing, manufacturing, astrophysics, horticulture, and other fields. In practice, color temperature is only meaningful for light sources that do in fact correspond somewhat closely to the radiation of some black body, i.e., those on a line from reddish/orange via yellow and more or less white to blueish white; it does not make sense to speak of the color temperature of, e.g., a green or a purple light. Color temperature is conventionally expressed in Kelvin, using the symbol K, a unit of measure for temperature based on the Kelvin scale.

Color temperatures over 5,000K are called cool colors (bluish white), while lower color temperatures (2,700–3,000 K) are called warm colors (yellowish white through red). This relation, however, is a psychological one in contrast to the physical relation implied by Wien's displacement law, according to which the spectral peak is shifted towards shorter wavelengths (resulting in a more blueish white) for higher temperatures.

Temperature Source
1700k Match flame, low pressure sodium lamps (LPS/SOX)
1850k Candle flame, sunset/sunrise
2400K Standard incandescent lamps
2550K Soft white incandescent lamps
2700K "Soft white" compact fluorescent and LED lamps
3000K Warm white compact fluorescent and LED lamps
3200K Studio lamps, photofloods, etc.
3350K Studio "CP" light
4100-4150K Moonlight
5000K Horizon daylight
5000K Tubular fluorescent lamps or
5000K cool white/daylight compact fluorescent lamps (CFL)
5500-6000K Vertical daylight, electronic flash
6200K Xenon short-arc lamp
6500K Daylight, overcast
6500K-9500K LCD or CRT screen
15000-27000K Clear blue poleward sky