the room. It is a measure of the proportion of
the outdoor illumination to the daylight illu-
mination received indoors.
Average interior daylight illuminance is
also calculated by graphic methods, such as
the Libbey-Owens-Ford™ “Sun Angle Calcu-
lator,” and by computer programs that con-
sider geographic location, time of day, time of
year, fenestration, room shape, and interior
finishes. The most sophisticated programs
produce a rendering of the interior showing
the relative luminances of room surfaces.
The simplest, most versatile, and most
reliable technique for studying the aesthetics
of daylighting is simulation by construction of
a scale model. Daylight behaves in the same
way in a scale model as in an actual building.
If studied under similar sky conditions, the
interior of the scale model appears exactly as
will the interior of the building. Miniature
photo electric cells are placed inside the
model to read illuminance values. But identi-
cal sky conditions are difficult to achieve by
placing the model outdoors; this has led to
the development of sky simulators that can
reproduce almost any sky condition.Energy Control
Photosensors(light-sensing devices) auto-
matically switch electric luminaires off when
the daylight contribution at selected interior
locations reaches prescribed levels. The
luminaires are automatically switched on as
the available daylight decreases. This kind of
switching has the disadvantage of calling
undue attention to the change; it may be
abrupt and jarring.
Dimming systems that allow a gradual
increase and decrease in light quantity are
more satisfactory. This is more pleasant and
may even go unnoticed. Sophisticated sys-
tems are designed with a built-in delay so
that a cloud passing rapidly across the sun
triggers no response.INTERIOR LIGHTING FOR DESIGNERS
Figure 5.18Prismatic glass block directs daylight toward the ceiling.