To alleviate scallops when using open-
reflector point-source downlights, use down-
light/wall-wash reflectors at the perimeter,
as indicated in figure 12.20, if the wall sur-
face is matte. If the wall surface is specular,
no adjustment is necessary; the intersecting
light pattern is unnoticeable on a mirror-like
surface.
Rectilinear fluorescent downlights with
sharp luminancecutoffshow an abrupt fall-
off of light at the upper part of adjacent
walls. This results in a shadow line along the
top of the wall, which often causes a space
to be perceived as dimly lighted (figure
13.10).Wall-washers or a continuous perim-
eter system will fill in this shadow. A similar
result is achieved by using a specular wall
finish in the shadow area with a matte finish
below it.
Irregular patterns of light are sometimes
desirable. A shaft of sunlight has intrinsic
value, as do some electric light patterns that
avoid a relationship to the physical form of a
space. The value of these irregular patterns
of light is that they serve as a temporary
visual stimulant.
Irregular light patterns are also success-
ful when they relate to an appealing attribute
of the physical space, such as a painting,
sculpture, plant, or architectural detail.
Unless specifically intended, however, avoid
irregular light patterns.Matte vertical surfaces
Three kinds of lighting systems are available
foruniformvertical surface illumination of
matte surfaces: (1) individual unit, point-
source wall-wash; (2) continuous, linear,
point-source wall-wash; and (3) continuous,
linear, diffuse-source wall-wash.Individual unit, point-source wall-
wash. To provide uniform illumination from
top to bottom, luminaires are placed parallel
to the wall at a distance of about one-third
the height of the wall. For uniform lighting
from side to side, the “square rule” applies:
luminaires are located on centers closer
than or equal to their distance from the wall.
The center-to-center spacing varies with the
ceiling height and the light intensity desired
on the surface.INTERIOR LIGHTING FOR DESIGNERS
Figure 13.10Sharp-cutoff luminaires produce shadows along the top of an adjacent wall.