contoursto redistribute light that would be
otherwise misdirected or trapped.
Other reflector contours
Compound contours, which provide asym-
metric distribution or maximum beam-
spread with a shape of minimum dimension,
are useful for producing uniformity of lumi-
nance from a position close to the surface
being lighted; for example, to light the ceiling
in a low-height room (figure 9.7).
Innumerable other possible reflector
contours can be mathematically defined and
tailored for a particular function. These
reflectors do not have a specific focal point.
Reflectors
Specular reflectors
Almost all reflector design presumes a com-
pact “point” source of light or a linear source
of light at the focus or other precise location.
The most compact source is an incandes-
cent filament in a clear bulb.
Large variations in beam control occur,
however, with the use of lamps that emit
light from a larger area, such as an arc tube
or a phosphor-coated bulb or tube. In these
cases the bulb or tube, rather than the fila-
ment, is the actual light source. This kind of
lamp is both a large source displaced from
the focus and a diffuse emitter. The result is
a diffuse or less precisely defined beam and
a reduced projection distance.
The first reflectors for electric luminaires
were designed by trial and error or by “long-
hand” mathematics (figure 9.8). Today,
computer-aided reflector design accounts
for all of the characteristics of a light source
and optimizes a reflector contour.Semi-specular reflectors
Although clear incandescent lamps in spec-
ular reflectors produce efficient beam con-
trol, there is often a need to smooth out
irregularities in the beam. These striations
are reflected images of the filament coil.
They are eliminated by a slight diffusion of
the beam, accomplished by using (1) an
inside-frosted lamp, (2) a lightly etched, fac-
eted, or hammered reflector surface, or (3) a
moderately diffusing lens in the beam path.INTERIOR LIGHTING FOR DESIGNERS
Figure 9.7Compound contour for maximum beam-spread (often
used to produce asymmetric distribution).