A means of color evaluation utilizing the temperature (in degrees Kelvin) to which a black object would need to be heated in order to produce light of a certain wavelength (or color). Substances, when heated, will tend to incandesce—or, in other words, as their constituent atoms or molecules absorb increasing amounts of energy, they will emit light and the wavelength of that light will vary by temperature and by substance. Iron, for example, when heated, emits light that is pale red; heated further, it emits white, then blue light. The black object described in terms of the evaluation of color temperature, is essentially a theoretical “perfect blackbody,” a substance so black that it absorbs all the light that strikes it. In theory, as it increases in temperature, it will emit colors in a predictable manner. For example, at 2000 Kelvin (or 2000 K), it will emit red light; at 5000 K, it will emit white light; and at 10,000 K, it will emit blue light.
Light bulbs are often described in terms of their color temperature, as it is the heating of specific substances within them that actually produces the light. A generic 100-watt incandescent bulb (which essentially produces light by heating its tungsten filament until it glows brightly) has a color temperature of 2860 K. Direct sunlight—which produces white light, or light possessing an even distribution of wavelengths (or colors)—has a color temperature of about 5000 K, and is considered an important characteristic of the standard viewing conditions for the evaluation of color.