The color temperature of any source of radiation is defined as the temperature (in Kelvin) of a black body or Planckian radiator whose radiation has the same chromaticity as the source of radiation. Often the values are only approximative color temperatures as the black body radiator cannot emit radiation of every chromaticity value.

The color of a solid is defined in terms of the CIE chromaticity coordinates X, Y and Z. The system is illustrated graphically in the form of the color triangle representing the chromaticity cordinates of all the colors. The sector of the spectral colors and the purple boundary delimit the area of all the real color regions. The achromatic point is located in the middle of the triangle.

The color temperatures of the commonest artificial light sources range from less than 3000K (warm white) to 4000K (intermediate) and over 5000K (daylight).