of automobile headlights at night demon-
strates that glare for the approaching driver is
a function of direction as well as intensity. It
also demonstrates that glare may be present
in an environment with little light.
Glare is also a function of luminance
area. Although a small area of luminance is
tolerable, a larger area of the same intensity
becomes uncomfortable. It is desirable to
reduce luminance intensities as the area of
luminance becomes more dominant in the
field of view.
In addition, glare is a function of loca-
tion. Within limits, the human eyebrow con-
ceals glare from overhead luminaires, but
not from poorly shielded, wall-mounted
luminaires or high-luminance wall surfaces,
as these elements are directly in the field of
view (figure 3.29).
Direct Glare
The late afternoon sun and an unshielded
electric light source are examples of the dis-
tracting influence of direct glare in the envi-
ronment. Direct glare is caused by the
lighting system; it is defined as excessive
light misdirected toward the eye.
Usually, the uncontrolled luminance of
an exposed light source produces glare. For
this reason, barelamps(the technical word
for light bulb) are rarely used in architectural
applications (figure 3.30).
When direct glare occurs in the normal
field of view, three main control techniques
are available. One is to limit the amount of
light emitted in the direction of the eye (figure
3.31). Shielding devices such as the hand,
used instinctively, and sun visors improve visi-
bility and restore visual comfort in this way.INTERIOR LIGHTING FOR DESIGNERS
Figure 3.29 Acceptable luminance values
decrease as the source approaches the center
of the visual field.