photographic material, and how to manage this energy to produce the desired
results.
a. What Light Is. Light is a form of radiant energy that travels in
wave motion. Radiant energy travels at the speed of light. The speed of
light is approximately 186,000 miles per second (mps) in a vacuum.
(1) Differences in wavelength and frequency distinguish one form of
radiant energy from another.
(a) Frequency is the number of waves that pass a given point in 1
second.
(b) Wavelength is the distance from the crest of one wave to a
corresponding point on the crest of the next wave.
(2) The product of wavelength and frequency is equal to the speed of
travel. Figure 1-1 illustrates a wavelength.
Figure 1-1.
A wavelength
b. The Speed of Light.
For a given medium, the speed of light is
constant.
(1) When light enters a medium of different density, the speed
changes. For example, the speed of light drops to about 124,000 mps when it
enters glass. Of course, this varies depending upon the refractive index of
the glass.
1-3
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