Guide to Portrait Photography, Step Three: Understanding White Balance and Color Temperature
By now you have probably discovered the White Balance menu on your digital camera or at least read about it in the camera’s instruction manual. Camera manuals really don’t explain White Balance and Color Temperature very well, leaving most beginning photographers confused as to what it is and why it’s important.
William Kelvin, a British physicist, discovered in the late 1880s that a cube of carbon heated to different temperatures glowed with different colors. Kelvin’s temperature scale, unlike the Celsius scale or the Fahrenheit scale started at “Absolute Zero,” the theoretical temperature at which all molecular action ceases. Kelvin discovered that as he heated the “Black Body,” it gave off different colors as it reached different temperatures on his scale, beginning with a dull red and continuing on through the visible spectrum of colors. The color temperature of the sky on an overcast day is 6000 to 7500ºK. that’s not to say that the sky is that hot, it means that that’s how hot Kelvin had to heat his cube of black carbon before it emitted that hue of colors. Color temperature is simply an easy way to describe colors in a quantifying way that everyone can understand. Everyone’s conception of what qualifies as being bright red may not be the same, but everyone’s understanding of 1000ºK is the same.
For those of us who started out shooting with film, color temperature is an old friend. We learned early about color temperature and need to have the right film loaded in our cameras; and we learned how to use color temperature-correction filters so if we had outdoor film loaded we could temperature-correct for tungsten lighting, etc. For those who have moved up to digital, the connection between color temperature and White Balance may not be clear. For those starting out with digital, the concepts of Color Temperature and White Balance may be confusing but the two are directly related.
Most digital cameras do a good job of selecting the correct color temperature when we are shooting in the full auto mode but you will get much better photos if you use the AWB (Appropriate White Balance) for the color temperature of the light you are shooting under. The serious photographers use a color temperature meter for measuring the temperature of the ambient light. A good color temperature meter like the Gossen Color-Pro 3F is expensive, close to $1000, so unless you are a professional photographer you probably won’t want to invest that kind of money into a color temperature meter. With a little practice, you can get good results using the color temperature charts that I’ve included with this article.
The important thing to remember that when shooting with auto-selected AWB and using filters, your camera may be canceling out the effect of the filter. Actually you can use the AWB to imitate the effects of various filters, but that’s the subject of another article. The important thing to learn now is that for the most natural-appearing pictures, set the AWB manually for the lighting conditions present.
Setting the AWB will be easy when shooting in the studio because you will simply set it for the temperature rating of the photofloods being used or for the strobes being used. A word about photoflood bulbs is in order here. Studio photoflood bulbs have both a color temperature and hours rating. For example, if the bulbs are rated for 6 hours, don’t use them after 6 hours of use. They will still work but their color temperature will have changed and will no longer fall within the usable range. It’s cheaper to replace the bulbs then try to guess the AWB every time you use them. If you have a color temperature meter, you can meter the light emitted and then seat the AWB but you can buy several hundred bulbs for what a color temperature meter will cost you.