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Chapter 11 ∣ Color
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actually a combination of roughly equal parts of all
the visible wavelengths. Using a prism, Figure 11-2,
white light can be broken down into six major colors:
red, orange, yellow, green, blue, and violet. When
sunlight is passed through a prism, a continuous
spectrum is created that blends smoothly from one
color to the next. Many other sources of light do not
produce a continuous spectrum. A sodium-vapor
streetlight, for example, may produce bright yellow
and blue, and also has dark regions in its spectrum.
This difference in light sources greatly influences
individual perception of colors.
Temperature of Light
The color of light is measured in degrees
Kelvin (K). In terms of color temperature, blues and
violets are the warmest colors; reds and oranges are
the coolest, Figure 11-3. This range of colors can be
demonstrated by heating a piece of metal called a
black body. As the black body is heated, it emits light y y
in a range of colors. Beginning with dull red, it moves
through orange, yellow, and white. If no chemical or
physical change occurs, the metal eventually emits
blue light. The color of light emitted from the black
body can be described by its temperature.
Behavior of Light
When light travels through a continuous medium,
it travels in a straight line. However, when light reaches
a surface or boundary between two types of material,
such as air or water, several things can happen. Some
of the light may reflect from the surface, while some
may pass through it. The light that passes through the
second material may refract, or bend. In addition, some
of the light may be scattered or absorbed.
Reflection
A beam of light coming toward a surface is called
the incident beam. After the beam is reflected, it is
called the reflected beam, Figure 11-4. Depending
on the type of material causing light to reflect, the
reflected beam may contain a different mixture of
light waves than the incident beam. If the mixture
is different, the new combination of wavelengths
gives the material its color. For instance, a red book
exposed to white light appears red because the
surface absorbs all other wavelengths of color in the
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Figure 11-2. A prism disperses the light that passes through
it, so our eyes can perceive individual wavelengths. The
shorter waves are more dispersed than the longer waves.
Because of this, the violet wavelength is always positioned at
the bottom and the red wavelength is always at the top.
Goodheart-Willcox Publisher
Figure 11-3. Approximate color temperatures of some
common light sources.
COLOR TEMPERATURE
Blue skylight
Overcast sky
Electronic photo flash
Evening light
Morning light
Midday sunlight (direct)
Studio lights
Household bulb
Candlelight
10,000 K–18,000 K
6250 K
6000 K
5000–6000 K
5000–6000 K
4500 K–5500 K
3200 K–3400 K
2500 K–3000 K
1800 K–2000 K