luminaires and adjacent surfaces. It is advis-
able to limit luminance ratios anywhere in
the field of view to less than 40:1.
Fenestration Sections
Windows placed on a single side of the room
(figure 5.2) are the usual method of fenes-
tration. To achieve useful work surface
illuminance throughout the room, limit the
depth of the room to twice the height from
the floor to a full-room-width window head.
For example, if the window head height is
10 ft, the optimum room will be no more
than 20 ft deep. Somewhat narrower win-
dows provide slightly lower illuminance
values, but the difference is minor.
This ratio of 1:2 may be increased to 2:5
as long as the reflectances of interior sur-
faces are high and carefully controlled. If
these ratios are exceeded, people seated in
the deepest part of the room will feel as if
they are receiving insufficient light, even if
they are provided with adequate electric
lighting.
Windows placed on opposite sides
double the feasible room depth for
daylighting. The opposite windows need only
occupy the upper part of the wall; the quan-
tity of interior light will be almost the same as
if the windows were full height, with the
added benefit of reducing the possibility of
glare (figure 5.3).
Skylightsare tools for delivering daylight
deep into interior areas of one-story build-
ings or into the top floors of multistory build-
ings. They also bring daylight into the lower
floors of multistory buildings through light
wells and reflective devices.DAYLIGHTFigure 5.2Unilateral section.Figure 5.3Bilateral section.