A Word About Color Temperature

by

William Lulow

Way back in the days of film, there were really two basic types of color film: Daylight and Tungsten. You could change one to the other by the use of special filters, if you didn’t have both, but that was about it. Tungsten film was balanced for use with indoor type lighting and Daylight film was balanced for use outdoors. Then there was always fluorescent light which could wreak havoc with color balance. (Since fluorescent light tended to be on the green side of the color spectrum, we would always wrap them with magenta filters when shooting indoors with strobes). Without getting too much into the science of color temperature, suffice it to say that it is measured in “degrees Kelvin.” This “standard” was named after Lord Kelvin (William Thomson), a British mathematician who lived from 1824 to 1907. He believed in being able to measure things. The Kelvin scale measures the relative coolness or warmth of various light sources. For instance, a match flame registers about 1,700 degrees Kelvin or 1700K. An ordinary table light bulb registers approximately 3200K, a fluorescent light about 3000K and daylight, about 5,500K. The higher the degrees Kelvin, the cooler or bluer the light. The lower the number, the warmer or yellower the light.

Ordinary daylight on a cloudless day registers about the same color temperature as that emitted by an electronic flash unit. This image was made on tungsten film but cross-processed in a developer made for daylight images, hence the bluish cast:

BlueMan(xproc)

Today’s DSLRs are capable of setting a “White Balance” for each exposure that automatically measures the degrees Kelvin of a scene and adjusts the color balance accordingly. There could be times when you might want to set the white balance manually. You have the ability to do that by adjusting the color temperature dial in the camera. If you are shooting at sunset for instance, and you want an interior to have a “warm” feel to it, you would set the white balance to 3200K. This would register the lights of a house normally, while giving the outdoors a bluish cast. This makes for an “inviting” looking image due to the warmth of the interior light. Here is an example:

Aura_0520(Dusk)WEB

The use of the white balance control in your DSLR can be a source of interesting images, but you must experiment with it (as with most photographic tools) until you learn how and when to use its features.