Graphics Reference
In-Depth Information
Light
We now turn to a more formal discussion of light, expanding considerably on the
simple ideas from Section 1.13.1. We start with the physical properties of light,
one of which is that it has many characteristics of waves, including a frequency.
Our eyes perceive lights of different frequencies as having different colors, but
since color is a perceptual phenomenon rather than a physical one, we treat it
separately in Chapter 28.
The second part of this chapter is about the
measurement
of light and the
various physical units we use to describe light. Since almost all of these can be
described as integrals of one basic quantity (radiance), we also briefly discuss a
few special integrals that arise often in rendering. Finally, although it is not strictly
a property of
light,
we introduce the measurement of the
reflection
of light by
surfaces, and compute the light reflected from a surface in two simple situations.
We live in a world in which electromagnetic radiation is everywhere. We're con-
stantly bathed in both heat and light arriving from the sun, radio and television
signals are present almost everywhere on Earth, etc.
Light
refers to a particu-
lar kind of electromagnetic radiation (of a frequency that can be detected by the
human eye, or nearly so). Because of this relationship to the human eye, light has,
over the years, been described not only in physical terms (like energy) but also in
perceptual terms, things having to do with the way that the human visual system
processes and perceives light. The most obvious of these is
color,
which we dis-
cuss in the next chapter in detail. We begin with the characteristics of the radiation
at microscopic and macroscopic scales, and then move on to a discussion of how
light is
measured
. The study of the measurement of radiation in general is called
radiometry,
and radiometric ideas are relatively easy to grasp, as is radiometry
applied to light (i.e., electromagnetic radiation of the kind that the human eye can
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