Biomedical Engineering Reference
In-Depth Information
14
Reflection
Light rays that are incident upon a surface can be transmitted, absorbed, or reflected.
In this chapter, we consider reflection that is produced by
specular surfaces
—
smooth (shiny) surfaces such as mirrors. As illustrated in Figure 14-1, the angle
of reflection for a mirror is equal to the angle of incidence. Referred to as the
law
of reflection
, all angles are measured with respect to the normal to the surface.
Not all surfaces are specular.
Perfectly diffusing surfaces,
1
such as a black-
board, have the same brightness regardless of the angle from which they are viewed.
Unlike specular surfaces, they do not appear shiny or glossy. In geometrical optics,
we are concerned with only specular surfaces.
RAY TRACING: CONCAVE, CONVEX,
AND PLANE MIRRORS
Concave Mirrors
Like converging spherical refracting surfaces and lenses, concave mirrors have plus
power and converge light. Figure 14-2 shows parallel light rays—traveling from left to
right—incident on a converging mirror. After reflection, the rays are traveling in the
reverse direction and intersect at what we'll call the mirror's secondary focal point,
F
.
The
center of curvature
for the mirror in Figure 14-2 is labeled “C.” Dotted
lines that emanate from the center of curvature are
radii of curvature
. Each of
these is, by definition, normal to the mirror's surface. Note that the law of reflec-
tion is followed, meaning that the angle of reflection for each light ray is equal to
the angle of incidence. As with a spherical refracting surface, the optical axis of a
mirror includes the center of curvature and focal point.
′
1. A perfectly diffusing surface is also referred to as a
cosine
or
Lambert surface
.
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