Color Temperature and White Balance
Definition
The colour of white light is described by its correlated colour temperature, expressed in kelvin. Low values are warm and orange, high values are cool and blue. Two reference points are standard in stage, film and television lighting: tungsten studio lamps at about 3200 K and daylight at about 5600 K. LED fixtures can often be set anywhere across that range, but their spectrum is usually less continuous than that of a tungsten lamp or of daylight, which affects colour rendering.
The guide
Colour rendering is rated with the CRI (colour rendering index, CIE 13.3) or with the more recent ANSI/IES TM-30 method, whose fidelity index Rf is calculated on 99 colour evaluation samples. Both compare the source with a reference illuminant. A high score means that reds and skin tones are reproduced faithfully. A source with a low CRI can make a costume or a face look wrong on stage, and more visibly on camera, even when its colour temperature is correct. The colour temperature describes the tint of the white, and the rendering index describes how accurately the colours it lights are reproduced.
White balance is the camera setting that matches the colour temperature of the light. The camera is set to the white of the lighting in use and then reproduces neutral tones correctly. A wrong setting shifts skin tones and scenery. Consistency matters more than an absolute value: a stage lit at one uniform white can be balanced by the camera, whereas a shot that mixes 3200 K and 5600 K sources cannot be corrected by a single white balance.
The rule
All sources in a shot are matched to one colour temperature before the camera's white balance is set.
Glossary terms
Sources
- Color temperature (Wikipédia, pointeur secondaire) : tungstène de studio vers 3200 K, lumière du jour vers 5600 K · en.wikipedia.org
- CIE 13.3-1995 : méthode de mesure de l'indice de rendu des couleurs (IRC/CRI) · cie.co.at
- ANSI/IES TM-30-20 : indices Rf et Rg calculés sur 99 échantillons, illuminant de référence · lightingservicesinc.com
- Alcon Lighting : introduction à TM-30-20 et comparaison avec l'IRC · alconlighting.com