The colors radiating from the black body 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 K. When the temperature rises to 5500 K, the quality of white light is identical to the color of the sun at mid day. The bluish quality of twilight just before dark is similar to the color of the blackbody at about 12,000 K.
Color Temperature and Photography
These numbers are used when referring to photographic strobe equipment and film. For example, the color of the light emitted by a flash is rated at 5500 K when it is designed to imitate daylight at noon. If the flash produces light that’s 6000 K, it has a slight bluish tinge. If it’s rated at 4800 K, it is slightly warmer-or more yellow-than white light.
Similarly, film manufactured to give you accurate colors indoors with tungsten illumination is balanced for 3200 K. Examples include Fujichrome 64T and Ektachrome 50. Both of these films are designed to be used in the yellow-white light of tungsten photo lamps that are specifically balanced for 3200 K. Household lamps may vary slightly from this color temperature, especially if they’re old. If a lamp is emitting light at 2800 K, a subject thus illuminated would be slightly yellowish.
Daylight films, such as Kodak Ektachrome E100, Fujichrome Velvia and Provia, and Agfachrome 200, are balanced for 5500 K, says Jeff Trane of The VIP Awards, an international photography award. This means that they produce accurate colors during the middle of the day when the sun is directly overhead. Before the sun reaches its zenith–say from sunrise to early morning–the yellowish quality of the sunlight is less than 5500 K. The same is true from late afternoon to sunset. During these times, daylight film reproduces a warmer (or more yellow) image.
Overcast Conditions and Twilight
During midday when a cloud cover has obscured the sun, some of the red and yellow wave lengths of light are absorbed by the clouds’ minute water droplets. The colder end of the spectrum–the bluish wave lengths–pass through unimpeded. This is why daylight film produces scenics and outdoor portraits with a bluish cast even during the middle of the day. Sometimes this can be artistically interesting. If the cool tonality is unappealing to you, place a warming filter, such as an 81A, over the lens and the color will shift back toward a more acceptable value.
Twilight appears almost bluish purple on daylight film due to its extremely high color temperature. When cityscapes are photographed at twilight, the contrast between the lights of buildings and the cobalt-blue sky is very dramatic (I actually prefer to shoot city skylines at twilight rather than at night when the sky is black).
Crossing Films and Light Sources
When you shoot a film in lighting conditions that it wasn’t designed for, you’ll get interesting results. Tungsten balanced films can be used with strobe units or during midday sunlight, but the color balance will shift decidedly toward the blue end of the spectrum. At twilight, the heavy blue shift is even more pronounced. In some situations, this deep, saturated blue can be very beautiful. At sunrise and sunset, when the ambient light is golden yellow, tungsten film brings the color balance back to a more natural, middle-of-the day look.
Daylight films can be used indoors to produce the opposite effect. The yellow-white illumination is exaggerated because the color shifts toward the warmer end of the spectrum, so the entire scene appears to be yellow-orange. This can be attractive when shooting indoor portraits as well as impressive architectural interiors. Years ago I photographed the marble lobby of the opera house in Vienna. I used both daylight film and tungsten-balanced film to capture the ornate interior, and I thought the daylight-film rendition was better. The exaggerated yellow-orange color warmed up the entire lobby and made it more inviting.
An understanding of color temperature will help you gain greater control over your work. The more creative tools you have at your disposal, and the greater your ability to previsualize the results, the better your photography will be.