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Graphic Communications
Copyright Goodheart-Willcox Co., Inc.
light. Only red wavelengths of the light spectrum are
reflected off the red cover.
Refraction
When light passes through a surface at any
angle other than a right angle, the speed of the light
changes and its direction is altered, Figure 11-5. In
other words, the light refracts. The type of material
affects how much the light bends. Refraction can
be demonstrated by placing a pencil in a glass of
water. The pencil appears to be bent at the surface
of the water. Light from the top of the pencil comes
directly to your eyes, while the light from the bottom
passes through the glass and water.
Scattering
Scattering occurs when light waves strike the
molecules of another substance. The molecules
cause the waves to scatter. A clear sky appears
blue because air molecules scatter a greater
amount of shorter wavelengths (blue) than longer
wavelengths in white sunlight.
Interference
When two light waves cross through the same
spot, they interfere with each other. The interference
between light waves occurs as constructive
interference or as destructive interference. To
illustrate interference, think of light as a wave with
crests and troughs. Constructive interference
occurs when the crests of multiple light waves pass
through the same point at the same time. At this
point, the light is brighter than any one wave can
emit alone. Destructive interference occurs when
the crest of one wave crosses the same point as
the trough of another wave. The trough reduces the
height of the crest, which leaves the spot very dim
or even dark.
Diffraction
Light waves usually travel in straight lines.
However, light waves diffract, or spread out, into
curving waves when passing through an opening or
slit, around a small object, or beyond an edge, such
as the outline of a person or a building.
The diffraction of light is useful when studying
colors in a light beam. For instance, scientists are
able to separate the colors of light from a star using
a diffraction grating. The grating uses thousands
of thin slits to diffract light. Each color in the light
diffracts by a slightly different amount, and the
spread of colors can be large enough to make each
color visible. Astronomers use this color information
to determine the makeup of the star.
Diffraction can also be a hindrance. As the
magnifying power of a high-quality microscope is
increased, for example, the edges of the object
being viewed begin to blur. The edges blur because
the light diffracts when passing over the edge on its
way to the eye.
Color Space
Both science and the graphic communications
industry require precise color definition and
classification. Words are imprecise in distinguishing
and describing color. What one person identifies
as yellow-green might be described by another as
light green or “greenish.” For this reason, various
systems have been devised to establish universal
terms for color classification.
Goodheart-Willcox Publisher
Figure 11-5. Refraction causes a beam of light to bend and
slow down as it passes through a substance. The angle of
refraction is less than the angle of incidence.
i
r
Normal
Plate
glass
i–angle of incidence
r–angle of refraction
Light wawaves
wav
wa
Goodheart-Willcox Publisher
Figure 11-4. The angle of an incident beam (right angles to
a surface), is equal to the angle of the reflected beam.
Normal
i r
Light waves
w w w
Incident beam
Reflected beam
Mirror
i–angle of
incidence
r–angle of
reflection