“blind spot” with horizontal rotation limited
to between 300° and 350°.
Whether surface-, pendant-, track-
mounted, or recessed, adjustable object
light housings are usually designed to shield
direct view of the lamp while avoiding undue
interference with the beam pattern of direc-
tional lamp sources.
The least expensive luminaires may lack
any brightness control, and the source glare
can be uncomfortable. Better-quality lighting
fixtures provide greater degrees of bright-
ness control, typically using an open reflec-
tor in recessed equipment and cube-cell
louvers or baffles in surface-, pendant-, and
track-mounted luminaires.
Louvers intercept some of the light in
the beam. Cube-cell louvers reduce light
output as much as 50 percent.Cross-baffles
are a more efficient method of shielding lamps
from the eyes because the light loss is mini-
mized.
When used to illuminate artwork and
larger objects, object lights are also supplied
with a linearspread lensto modify the distri-
bution and soften the edge of the beam.
Linear spread lenses are typically made of
borosilicate glass with a fluted pattern; they
are usually designed to spread the beam in
one direction only and are rotated as
required during luminaire focusing. Without
the spread lens, the same object light
source provides a symmetrical, concen-
trated beam-spread suited to smaller
objects and those that require a greater
intensity of illumination or “punch.”
Object lights contribute to a moderate-
to high-contrast setting because they intro-
duce nonuniform illumination. Medium- to
wide-beam lamps give moderate contrast;
narrow-beam lamps give high contrast.
Task Lights
Taskluminaires bring the light source close
to the surface being lighted. They are useful
for work surfaces of systems furniture, which
may receive insufficient light from an over-
head lighting system because of shadows
from vertical partitions and furniture-
mounted high shelves and cabinets.
Local task luminaires are often energy-
effective and useful for reducing reflections
in VDTs. Task lighting uses less power
because the source is closer to the surface
being lighted. Task luminaires can provide
the illuminance required for paper-based
visual tasks while allowing the ambient light
to be of a lower illuminance and decreasing
the chances of distracting VDT screen reflec-
tions.
Task luminaires are often mounted under
a cabinet or shelf that is directly over the work
station (figure 12.49). This location is in the
reflected glare zone, however; the luminaire
may produceveiling reflectionson the work
surface. This is eliminated by using optical
lenses for the luminaire that block the per-
pendicular light rays and convert them to rays
that fall on the task from the side and thus do
not cause veiling reflections.
Adjustable task luminaires are usually
mounted at one side of the task. An adjust-
able arm permits positioning the luminaire to
suit the task, maximizing task visibility. An
asymmetric light distribution is sometimes
incorporated to direct light more uniformly
over the task area.Soffits
A lightingsoffitis used for task light (focal
glow) rather than ambient light. It is located
adjacent to a wall or similar vertical surface
and is sometimes used to light niches. The
top is often closed and all light is directed
downward (figure 12.50).
Over work areas, reflectors increase the
useful light (figure 12.51); open louvers or
lightly etched plastic or glass perform best.
Matte finishes for work surfaces minimize
specular reflections (figure 12.52).LUMINAIRES