Skylights come in a variety of shapes
and sizes. They are made of clear, pat-
terned, or translucent glass or various kinds
of plastic. Clear, gray-tinted, or milk-white
acrylics are best for this purpose; their opti-
cal properties are similar to glass, and they
are easier to maintain.
Flat skylights have both drainage and
dirt-accumulation problems. Domed or
slanted skylights mitigate these drawbacks
(figure 5.4). Although a domed skylight is
“self-cleaning” on the outside, dirt still col-
lects on the inside, making a program of
periodic cleaning as important with skylights
as it is with electric luminaires.
Depending on the shape of the room
and the location and size of the skylight,
brightness control will be necessary in areas
with demanding visual requirements. If
directly exposed to view from below, at
angles in the glare zone, skylights often
produce excessive luminance and cause dis-
abling veiling reflections on tasks. Light from
skylights is controlled with the use of deep
wells, splayed wells, and louvers, preventing
any view of the skylight at unsuitable angles
and minimizing veiling reflections.
Diffuse (milk-white) plastic or glass sky-
lights diminish the biological benefits of day-
light by obscuring the view of the weather.
Clear glass or plastic skylights, however, pro-
duce more heat gain for a given unit of
illuminance at the work surface below and
may admit direct sunlight in undesirable ways.
An exterior shield that shades the skylight
from direct sun but allows daylight to pene-
trate reduces the heat load. For colder cli-
mates,double glazing—two thicknesses of
glass or plastic with an air space between—
reduces conductive heat loss in winter.
Clerestories have all the attributes of
skylights; because they occur in the vertical
rather than the horizontal plane, they can be
oriented to prevent the penetration of direct
sun (figure 5.5). When built in combination
with a light shelf, a clerestory reflects great
quantities of daylight against the upper ceil-
ing yet blocks the view of the glaring sky from
below (figure 5.6).
When facing the same (or opposite)
direction as the main windows, the clere-
story extends the room-depth limitations
(figure 5.7). When clerestories are located
on walls opposite each other, as was often
the case in early church buildings, these ver-
tical glazing sections are calledroof monitors
(figure 5.8). A series of parallel clerestories
is suited for large, low-roofed structures
such as factories and warehouses; this is
called asawtoothsection (figure 5.9).
To maximize the light delivered by the
clerestory, it is recommended that the roof
directly below the clerestory and the adja-
cent interior ceiling area be diffuse and
highly reflective.INTERIOR LIGHTING FOR DESIGNERS
Figure 5.4Skylight sections.