Interior Lighting for Designers

duced by reflecting contours. Because the

light source remains visible, materials such

as clear glass and plastic are ineffective for

glare control.

Semi-diffuse (spread) transmission

Translucent materials emit light at wider

angles because of configurations on at least

one side of the material (figure 9.11). A

slight redirection of the transmitted beam is

achieved by minor surface irregularities,

such as shallow facets or flutes, which

smooth out imperfections and striations. A

greater degree of diffusion is achieved by

etching, sandblasting, hammering, and

matte aerosol sprays applied to the outer

surfaces; or the interior of the material is

modified to achieve the diffusion. Semi-dif-

fuse materials provide lamp concealment

and glare control.

Diffuse transmission

Diffusetransmission disperses light in all

directions and eliminates the directional

quality of the beam (figure 9.12). Full diffu-

sion is achieved by using opal glasses and

plastics that incorporate microscopic parti-

cles and remove all directionality from the

transmitted beam.

Refraction

When a straw is placed in a clear glass of

water, it appears to bend at the point where

it enters the water. This is because the

speed of light changes when a light ray

passes from air to water; the phenomenon is

calledrefraction.

A similar result occurs when light passes

from air to clear glass and plastics. When

these transparent materials are formed into

prisms or lenses, they become techniques

for controlling the direction and, conse-

quently, the distribution of light.

LIGHT CONTROL

Figure 9.12Diffuse transmission.

Figure 9.10Direct transmission. Some first-surface
reflection occurs with all forms of transmission.

Figure 9.11Semi-diffuse (spread) transmission.