Issue 6: Color & Design

The concept of color temperature is an integral part of photography, and yet many photographers are not really sure what it means. Color and temperature don’t seem to have a direct relationship with each other, but light sources are often defined in terms of their color temperature, which is allied with setting the white balance in digital photography. In addition, the measurement of color temperature is in Kelvin degrees. What does all this really mean?

Kelvin, like Fahrenheit and Centigrade, is a scale for measuring temperature. Zero degrees Kelvin (this is defined as absolute zero where there is no molecular movement) corresponds to -459.67? Fahrenheit. The relationship between color and Kelvin temperature is derived from heating a “blackbody radiator” (think of this as a piece of black metal) until it glows. The particular color seen at a specific temperature is the color temperature. When the blackbody is hot enough and begins to emit light, it is dull red. This is about 2000? Kelvin and it corresponds to the color we can see in glowing coals in a fire or the red/yellow lava from a volcano (#1). As more and more heat is applied, it glows yellow, and then white, and ultimately blue.

1 All Photos © 2010, Jim Zuckerman, All Rights Reserved

The colors radiating from the blackbody are correlated to colors we are familiar with in our daily lives. The color emitted from a tungsten lamp in your living room is identical to the yellow-white glow when the blackbody radiator temperature is approximately 3200? Kelvin. When the temperature rises to 5500?, the quality of white light is identical to the color of the sun at midday (#2). The cobalt blue color of twilight just before dark is similar to the color of the blackbody at about 8000? Kelvin.

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These numbers are used to understand, for example, how flash effects your images, and may influence your white balance settings. The color of the light emitted by a flash is rated at 5500? by many manufacturers; it is designed to imitate noon daylight (#3). If the flash produces light that is 5800? Kelvin, it has a slight bluish tinge. If it is rated at 5200?, it is slightly warmer, or more yellowish, than white light.

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Similarly, film manufactured to give you accurate colors indoors with tungsten illumination is balanced for 3200? Kelvin. Examples include Fujichrome 64T and Ektachrome 50. These films are designed to be used in the yellow-white light of photofloods that are specifically balanced for 3200?.

Since film is not relevant to most of us now, a setting of 5500? Kelvin as the white balance in digital cameras is just like using daylight film. This means that if you shoot indoors with tungsten lights, the pictures will have that yellowish cast just like the interior of the Vienna opera house (#4). I purposely used a daylight white balance to make the scene golden. If I had used 3200? Kelvin for the white balance, the tungsten lights would be reproduced with the correct color balance (#5). Different cameras indicate this white balance in different ways. Some will have an indoors setting while others will show a light bulb icon. More sophisticated camera bodies allow you to dial in 3200? K. These all mean the same thing—that you can expect proper colors when shooting under tungsten lights.

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