Colour Temperature

Light sources may have different colours, and even sources of apparently white light (such as house lights or daylight) may have slightly different colours, which can be measured as colour temperature.

Tungsten light has a colour temperature of 3200 Kelvin, and daylight is approximately 5500 Kelvin.

In a location where daylight and tungsten colour temperatures are mixed, the scene can be exposed with a mixture of colours, if there are two apparent sources (left). The white balance of the video camera determines which light appears white, usually the light on the actor's face.
To create the impression that the scene is lit entirely by one source (the window), the lighting can be balanced for daylight or tungsten:

Balanced for daylight:

Balanced for tungsten:

The white balance of the video camera corrects for either daylight balance (below left) or tungsten balance (below right), making them appear as white.

The windows appear brighter if the lights are filtered, or darker if the windows are filtered:

Frame enlargements from The Grey Fox and The Fly.

White Balancing works on the principle of adjusting the amount of red and blue in the picture to equal the amount of green. This equal combination of the three primary colours produces white:

Illustration from the Society of Television Lighting Directors

Note: Using coloured gels (or diffusion to soften the light) decreases the intensity and may require a larger or additional light.

Go back to Four Variables of Light.

Return to FILM 250 Course Materials.