Models of artificial sky-

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 geometry or heavily obstructed windows. Models 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 distribution.

There are two basic forms of artificial sky: the rectangular and the hemispherical as shown in Figure 8. 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. The hemispherical sky may be a diffusely reflective opaque dome surface, illuminated from below, or a translucent dome (hemispherical), with lighting mounted behind.

                             
Fig. 12 Rectangular mirrored artificial sky
Fig. 13 Sky dome artificial sky