5.0 Color Balance
Description
This article is from the Gross
Specimen Photography, by Ed Uthman, MD
5.0 Color Balance
We perceive a sheet of paper illuminated by an incandescent bulb to be just as white as if it were illuminated by direct sunlight. This goes along with our concept that "white" light is composed of light of all colors. This is true to an extent, but various "white" light sources produce their component colors in varying proportions. For instance, the surface of the sun has a temperature of about 6000 Kelvins and has much more blue light in it than the radiating surface of a tungsten filament glowing at 3200 Kelvins, which has more red light. This relation between temperature of a glowing object and its color is well known to most people (although not by its scientific name - Wien's First Law), since we are taught from the fifth grade that a blue flame is hotter than a red one.
Although the neurological visual processing system behind our eyes compensates for this variability, the film in a camera cannot. The solution is to make film where sensitivity to the colors of the spectrum is specifically balanced for the color distribution of the light source. When shooting in daylight or with an electronic flash, we need to use "daylight" film. Alternatively, when using incandescent lights (such as the floods on the copy stand), we need to use "tungsten" film. This is not some theoretical consideration. If you try to use daylight film with the floodlights you will get an unacceptably orange picture; conversely, shooting tungsten film with a flash will produce a picture that looks like it was painted by Picasso during his "blue" period.
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