Color Temperature in photography

The color quality of light and film is defined by a system where each light source and the color balance of film is identified by its color temperature.

What exactly is color temperature? Many years ago Lord Kelvin, an English scientist, invented a method designating color temperatures on a scale that has become known as the Kelvin scale. The specific temperature numbers on this scale are derived from actual wavelengths of light emitted from a dead black, nonreflecting material that physicists term a "black body radiator."

As a black body radiator is heated, it generates light: dull red, then a more brilliant red, orange, yellow, and eventually, an intense blue. Visually matching the color of the black body radiator as it is heated to the color of a specified light source and then measuring the temperature of the black body radiator at this point gives us the color temperature of the light source on the scale beginning from absolute zero. Color temperature is annotated as degrees Kelvin. So, daylight film is labeled 5500K, tungsten film 3200K.

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