Color Temperature

“WHITE” LIGHT ISN’T WHITE

“White” light exists mostly in theory; at any given time, the light we think of as “white” is actually somewhere between a pale yellow and a pale blue. This range is referred to as “color temperature”. It can best be demonstrated by setting the “white balance” on a digital camera to “daylight” and taking a picture under incandescent light. The resulting image will be slightly yellow, because incandescent light is yellower – has a lower color temperature – than does daylight. Likewise, setting the white balance to “tungsten” and shooting a scene lit by daylight will yield a photo that is slightly bluish, since daylight has a higher color temperature than does tungsten light.

For this photograph, the white balance was set to “daylight” (or “outdoor”).

For this photograph, the white balance was set to “tungsten” (or “indoor”).

Color temperature is measured in “degrees Kelvin,” abbreviated as “K.” As mentioned above, the bluer a light is, the higher its color temperature will be. Below is a table of approximate color temperatures for common light sources:

Color TemperatureLight Source

1700° K               Match Flame

1850° K               Candle Flame

2000°–3000° K      Sun at Sunset or Sunrise

2700°–3300° K     Household Incandescent Light

3000° K               Standard Incandescent Theatre Lighting

3050°–3400° K     Theatre Lighting / Photofloods

5500°–6000° K     Typical Daylight

6500° K               Overcast Daylight

So what does this mean? From what are these numbers derived? The temperature is referenced to that of a standard “black body” – a block of carbon which, when heated to specific temperatures, emits light of specific colors. The Kelvin scale (named after British physicist William Kelvin) is a variation of the Centigrade/Celsius scale, except that rather than its being keyed to the freezing point of water, it is based on “absolute zero”. If you subtract 273 from a Kelvin temperature, you will have its Celsius equivalent. You may be thinking that none of the colors above looks like “white”…. and you’re right. First of all, they are merely approximations and not, as such, accurate. Secondly – and more important – the eye (or, more accurately, the brain) adapts. We tend to automatically “white balance” ourselves to the dominant light source in our environment at any given time. If, for example, you spend a significant amount of time outdoors during the daylight hours and then go into your house or apartment, the interior lighting may look yellowish for several hours, until your brain “white balances” to its new environment. This is something you should remember, by the way, when you’re writing the first few cues of your show.