Model studies can be used to predict
daylight penetration into any building. This is the only reliable prediction method in the
case of unusual situations, complex geometries or heavily obstructed windows. Model
studies can be carried out under outdoor conditions, but the limitations imposed by
weather variations can be quite severe.
The artificial sky simulates the
standard overcast sky conditions, giving either uniform luminance or the CIE luminance
There are two basic forms of
artificial sky: the hemispherical and the rectangular (Figure 13). The former may be a
diffusely reflective opaque dome surface, illuminated from below, or a translucent dome
(hemispherical), with lighting mounted behind. The rectangular sky has a luminous ceiling
and four strictly vertical walls lined with mirrors. The multiple reflections between
accurately parallel opposing mirrors give an infinite horizon effect. The mirror glass
absorption through multiple reflections ensures a luminance distribution similar to that
of the CIE sky.