Color temperature

Color has an intimate relation to temperature. When a flame burns at a high temperature, the color is blue; at a low temperature, the color is red. The measurement criterion of "color temperature" is used to assign objective numeric values to the condition of light when we see a color. Color temperature is expressed in Kelvins, based on an imaginary object called a black body which absorbs all light.

The sun at noon is 5,000 degrees Kelvin; at morning or evening it is 4,000 degrees Kelvin. A daylight fluorescent lamp is 6,500 degrees Kelvin, and the average computer screen is also 6,500 degrees Kelvin.

The lower the number, the closer the color is to red; the higher the number, the closer to blue. This explains why the same red item of clothing will appear differently out of doors than under a fluorescent lamp indoors.

Compare:Understanding Color/Measuring color and colorimetrics