Daylight, incandescent, fluorescent, and other light sources all have color characteristics that vary significantly. The appearance of an object’s color is therefore affected by the lighting conditions under which it is viewed. Our eyes and our brain compensate for different types of light; for example, a white object appears white whether it’s viewed outside under the sun or inside under a light bulb. But color films need to be balanced to compensate for different types of lighting and to render not only whites as white (white balance) but to give the colors in an image the same appearance as they had in the original scene.
Color films are optimized to remove specific color casts from images by neutralizing the particular color temperature of a light source. The color temperature of light is defined in degrees kelvin (K), which is the standard by which the varying hues of light sources can be compared. The two most common color-balanced film stocks are 5500K daylight (D), for use outdoors or with electronic flash, and 3200K tungsten (T), for ordinary household lighting.