Datasheet

27
UNDERSTANDING COLOR AND COMPOSITION
Figure 1.32 A calibration chip chart. This le is included on the CD as chip_chart.tif.
A Note on Color Temperature
Color temperature is based on the wavelength of light emitted by a material when
it is heated. Technically speaking, if a light source is said to be 5500 kelvin, it emits
the same wavelength of light, and the same color of light, as a black body radiator
heated to 5500 kelvin. A black body radiator is a theoretical material that absorbs
100 percent of the radiation that strikes it when the body is at absolute zero (–273 C°).
Although there are no true black bodies in the real world, graphite and various met-
als come close. In the original experiments by William Kelvin (1824–1907), a block of
heated carbon was used. The kelvin, on the other hand, is a measurement of tempera-
ture that adds 273 to the temperature read in Celsius. The kelvin measurement only
refers to the thermal temperature of the theoretical black body radiator and is not the
actual temperature of a light source. In other words, a fluorescent lightbulb does not
have to reach a real-world 4000 degrees kelvin to produce the same color of light as
the black body radiator at 4000 kelvin; instead, the color of the bulb is roughly corre-
lated to the color of the heated black body.
When a material is heated to a temperature above 700 K (700 kelvin), it emits
visible light. At temperatures close to 700 K, the light wavelength is long and the per-
ceived light is red. At temperatures above 6000 K, the wavelength becomes shorter
and the perceived color shifts to blue. The chart in Figure 1.33 indicates the color
temperature of various light sources and their perceived colors. The colors represented
are only a rough approximation. In addition, the color temperatures listed for each
light source are an average; depending on the circumstance or the method of manufac-
ture, color temperatures can easily vary by hundreds of kelvin.
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