Interior Lighting for Designers

Diffuse reflectors
The reflection of light from a perfectly dif-
fuse, flat surface is multidirectional, giving a
circular distribution curve; the angle of
reflection is independent of the angle of inci-
dence. With incident light dispersed in all
directions, the beam is wide (figure 9.9);
because of this lack of directional control,
long projection distances are impractical.
The shape of a diffuse reflector has little
influence on the resulting direction and dis-
tribution of light. Diffuse reflectors are often
useful in luminaires that provide uniform,
ambient brightness in a space, but they are
unable to direct light toward a surface, such
as the workplane.

Reflector materials
Aluminum is the material most frequently
used for the fabrication of reflectors. It can
be stamped, spun, hydroformed, or extruded
into almost any desired shape or contour; it
can be processed chemically and electrically
to make it more specular; and it can be
sandblasted or etched chemically to provide
varying degrees of semi-specular reflection.

A hard, protective surface layer of high

transparency produced by the anodizing pro-

cess prevents scratching and abrasion of

specular aluminum surfaces and makes

cleaning practical.

Transmission

Transmissionof light through a material is

affected by two things: (1) the reflections at

each surface of the material and (2) the

absorption and redirection within the mate-

rial (called refraction; see page 111). Just as

a continuous degree of reflection exists from

mirrored, fully specular surfaces to matte,

fully diffusing ones, a similarly continuous

degree of transmission exists from fully

transparent, clear materials to fully diffusing,

translucent ones.

Direct transmission

Transparentmaterials leave the light distri-

bution unchanged (figure 9.10). They are

used as protective covers for absorbing or

reflecting infrared or ultraviolet radiation or

where a change in the color of light is desired

while maintaining the light distribution pro-

LIGHT CONTROL

Figure 9.8Parabolic reflector construction guide.