Daylight
The goal of daylight design is to provide visual variety with controlled
brightness contrasts.
A principal characteristic of daylight is its
variability. The color of daylight changes with
the time of day, the cleanliness of the atmo-
sphere, and the interreflection of surround-
ing objects. The intensity of the sun changes
with the time of day, the time of year, and
the latitude of the site. The luminance of the
sky depends on whether the light is coming
from an overcast sky, from a clear sky only,
or from a clear sky and direct sunlight.
Daylight has two components: sunlight
and skylight.Sunlightis the directional beam
emitted by the sun;skylightis the diffuse
reflection of light from particles in the atmo-
sphere.
Direct sunlight is usually an impractical
source for interiors unless it is shielded. Just
as electric luminaires are designed to reduce
glare, direct sunlight entering interior spaces
requires careful control. For critical seeing
tasks, sunlight often causes excessive lumi-
nance differences that result in discomfort
and poor visibility. This high contrast in the
field of view inhibits the eye’s ability to adjust,
leading to visual fatigue and disturbing the
accommodation needed for clear vision.
Skylight, on the other hand, is a useful
source without shielding. Although special
building configurations or controls are neces-
sary to make skylight acceptable for
horizontal tasks at the workplane or for dis-
playing art, it is used with less control to light
noncritical seeing areas such as corridors,
stairwells, cafeterias, and seating areas.
People require changing stimuli to
remain sensitive and alert. For example,
gazing out the window at distant objects pro-
vides relief for the muscles of the eye. And
the constantly changing nature of daylight
satisfies our biological and psychological
needs for change—a view of the sky pro-
vides information about the time of day,
which helps maintaln our biological cycles,
and the varying light intensity as a cloud
passes in front of the sun provides respite or
stimulation, which helps reduce monotony.
The proper introduction of daylight into
the interior is the simplest way to provide this
change. The goal of daylight design is to pro-
vide visual variety with controlled brightness
contrasts.
Comfort requires moderate changes.
Monotony will cause fatigue, but so will
overstimulation. Excessive contrast provides
emotional appeal but also impairs visual per-
formance. The sudden appearance of a