Interior Lighting for Designers

winter provide natural climatic control when
placed in front of south-facing windows.

Glazing Materials

Glazing materials are available with a wide
range of heat and light transmittance, color,
and prismatic control. Because of its resis-
tance to abrasion, glass is the preferred
material; where breakage is a concern,
acrylic or polycarbonate is substituted. Both
glass and plastic can be tinted in warm, neu-
tral, or cool gray tones to reduce the trans-
mission of light and heat yet remain
transparent to vision. Saturated colors are to
be avoided except in carefully designed art
(“stained”) glass windows.
Translucent glazing materials that trans-
mit diffused light but obscure vision include
etched, sandblasted, opal, and patterned
glass and plastic. Many translucent materi-
als become excessively glary with exposure
to the sun and will be distracting when seen
from task areas. Because they prevent a
view of the outside, their psychological value
is minimal. As diffusion increases so does
the area of luminance and the possibility
that the window or skylight will become a
source of glare.
Selectively transmitting materials allow
the desirable wavelengths of the visible

spectrum to pass but reflect or absorb the

radiant heat energy. Directionally selective

glass blocks and prismatic glass or plastics

refract light for directional control.

When installed vertically, prismatic glass

block walls are used to reflect daylight onto

the ceiling of a room, increasing illuminance

values deep in the interior and removing the

glaring sky from view (figure 5.18). When

installed horizontally, as with glass-block

pavers, they transmit light yet maintain a low

surface luminance even when exposed to

direct sun.

Quantity

Because of the great variety of changing sun

and sky conditions, it is impractical to pre-

dict precisely the interior illuminance pat-

terns derived from daylighting. By knowing

the size and position of windows and using

tables of average daylighting conditions for

various locations and orientations, the aver-

age amount of available daylight that will

enter a space can be determined, but not

the precise amount at any moment.

Interior daylight illuminance values are

often expressed as a daylight factor. The

daylight factor accounts for light received

directly from the sky, light reflected from

external surfaces, and interreflections within

INTERIOR LIGHTING FOR DESIGNERS

Figure 5.16Skylight shades.