Interior Lighting for Designers

Prisms
A beam of light is displaced at the surface of
a transmitting material. If the material is
formed with two parallel “faces,” the dis-
placements neutralize each other; no angu-
lar change in the direction of the beam
occurs, only a slight displacement (figure
9.13a). If the opposite faces are not parallel,
the unbalanced refraction permanently
alters the direction of light (figure 9.13b).
Light rays deviate toward the perpendic-
ular when entering a material with a higher
index of refraction and deviate away from the
perpendicular when entering material with a
lower index (figure 9.14).
Aprismis a transparent body bounded
in part by two nonparallel faces. A beam of

light projected through one face is emitted in

a different direction through another. By pro-

viding the proper angle between prism faces,

light is emitted in a desired direction (figure

9.15).

Lenses

Alensis formed by two opposite refracting

surfaces, which have a common axis. It may

be thought of as a multiple array of prisms

with a continuously changingincluded angle

to produce an organized distribution of light

(figure 9.16). Two basic kinds of lens sys-

tems are used: convex and concave.

Theconvex(positiveorconverging)lens

is thicker in the middle than it is at the

edges. Its focal point lies on the axis, at the

INTERIOR LIGHTING FOR DESIGNERS

Figure 9.20Distribution of light through a Fresnel lens.