THEORY OF LIGHT AND OPTICAL PRINCIPLES
Light is the photographers medium, and a
photograph is the image of a pattern of light recorded on
film. The word photography means writing or drawing
with light. Without light there could be no vision or
photography because it is light reflected from the world
around us that makes things visible to both our eyes and
the eye of the camera. The nature of light has a critical
effect on the pictures you make. Few photographers
actually understand much about light. But they are not
alone. Scientists have never been able to agree fully
about the nature of light. However, certain useful things
are clear and well understood about how light behaves.
Light is a form of electromagnetic radiant energy to
which the eye is sensitive. It travels at tremendous speed
from its source, such as the sun, a fluorescent lamp, an
electronic flash, or whatever source is used. It has an
effect on the materials it falls on, skin becomes tanned,
and fruit is ripened by the light of the sun. Depending
on the way in which light is received or rejected, a
complex pattern of light, shade, and color results.
Other types of radiant energy, such as radio waves
and X rays, are similar to light but the eye cannot see
them. Thus they are not light. By definition, light is
electromagnetic energy visible to the human eye. All
other electromagnetic energy is invisible, therefore, is
not considered light. Ultraviolet and infrared radiations
are two such invisible radiations that are of concern to
Light makes up the visible spectrum, which is a small
part of the entire electromagnetic spectrum (fig. 1-1).
Figure 1-1.The electromagnetic energy spectrum.