The Color of “White”
Take two identical squares of red paper. Put one on white paper, the other on blue. View them one after the other. The two squares will seem to be different shades of red.
What’s going on here? We're catching our eyes in the act of second-guessing the color of everything we see. Even skeptics tend to think of vision as a simple, linear process. Researchers probing the details of vision say otherwise. Francis Crick, codiscoverer of the structure of DNA and a CSICOP fellow, devoted a book to summarizing vision research and its implications for understanding human consciousness (The Astonishing Hypothesis, Scribner’s, 1994). Visual experience is profoundly synthetic. Raw data from the retinas undergo extensive processing and interpretation, starting in the retina itself. Structures throughout the brain join in shaping what we seem to see so naturally through our eyes. But seeing is not believing.
The red-squares illusion illustrates the Land effect (discovered by Edwin Land, who went on to invent Polaroid photography). Here’s the problem: We never see the “actual colors” of objects. All we get to work with are the wavelengths of light they reflect. that reflected light can be affected by the object’s actual color or by the color of the light under which we view it. Or both. White paper under red light looks red. Red paper under white light looks red too. Yet we can usually tell them apart. How?
Apparently, still further up the visual-processing ladder, color information from one part of the visual field (the paper) is compared with that from the background. The brain tries to subtract the effect of colored illumination to restore the “actual” color of objects. That is the Land effect, and it’s why a white jacket still looks white instead of orange under the setting sun. Like most of the brain’s subterfuges, the Land effect can be fooled. Viewing those two red squares on different-colored backgrounds tricks the brain into thinking that the red square on the blue background actually lies under blue light. So it “compensates” by changing the square’s perceived color.
What’s remarkable is not that the brain’s color compensating apparatus can be fooled, but how well it usually works. We live our lives under many different colors of “white light” and hardly ever notice. Ever take snapshots indoors without flash? The photos come out with a strong orange cast. Were you about to say an “unnatural” orange cast? Bite your tongue! That ruddy tint is altogether natural. The light from a household table lamp really is that much redder than sunlight.
Professional photographers measure the color of “white” light in degrees Kelvin (degrees Celsius above absolute zero). “Color temperature” corresponds to the color of light that would be radiated by an ideal black body heated to that temperature. Lower temperature means redder; higher temperature means bluer. As shown in Figure 1, household incandescent lighting has a relatively low color temperature-about 3,000° K. (Only open flames-candles, campfires-are lower.) By contrast, direct sunlight has a color temperature of about 5,400° K., much bluer.Photographic film can’t compensate for the color of ambient light like as your brain does. Your film reproduces color most accurately at 5,400° K, the color of direct sunshine (and photoflash units). Your available-light indoor photo is taken at 3,000° K. You don’t see the color difference, but your film does. Result: orange snapshots.
Real life is a symphony of color temperatures most of us never see (Figure 1 again). Incandescents used in television and movie studios are bluer than household lighting, about 3,400° K. (Professional motion-picture films are balanced for this light; in low-budget movies, the view from the livingroom window often has a blue cast. Producers with more money put orange gels over the windows.) Open shade is about 400° K bluer than sunlight. Some of the high-intensity lights now used in Hollywood hit 6,200° K. They require orange gels to match sunlight! Outdoors at night, these units are often used without gels for maximum light output. That’s one reason that artificially lighted night exteriors in movies like Terminator 2 look so blue.
Since the 1970s, Hollywood has delighted in teasing us with the colors of white. Letting the colors shift suggests gritty realism: Remember the orange interiors of the Godfather films? Consider the way police station interiors are often lighted in cop movies. Most of the light looks white (3,400° K). The windows go blue (5400° K). And the little fluorescent lamps on everybody’s desk look green. Green? Color temperature isn’t the only variable in “white” light. Most fluorescents have a green spike in their color spectrum: They emit a disproportionate share of their light at green wavelengths. Untrained humans never see that extra green, but film does.
Why don’t home videos show the colors of white so strongly? Camcorders compensate for the color of ambient light much as the brain does. As for professional videographers, they point their lenses at a white card and push a "white balance” button. It’s their way of telling the camera, “Hey dummy, this is white.” The camera then adjusts its red, green, and blue gain until the card reads truly white, compensating for color temperature and color spectrum in one operation.
What are the lessons of all this? First, if you shoot snapshots indoors without flash, stop waiting for the magic day when your pictures will stop coming out orange. They never will. Second, the next time you’re tempted to accept the evidence of “your own eyes” without additional corroboration, remember about the color of white. It isn’t just your eyes that see, it’s your brain — and some of the tricks your brain performs to “improve” your visual experience can distort it as well.