Constraints on reflectance in artificial sky domes

Reflective dome type artificial skies are effective tools in daylight research and design, but need careful design if they are to reproduce a desired sky luminance distribution faithfully. In particular, inter-reflection within the dome can make the sky luminance distribution too uniform; the higher the dome reflectance the worse this problem is, despite a widespread assumption that high reflectance is desirable. This paper gives a general method for estimating the magnitude of this inter-reflection. It shows, for example, that a winter CIE clear sky luminance distribution cannot be obtained inside a dome of reflectance greater than 0.6. A CIE standard overcast sky can however be achieved inside a dome of high reflectance, provided considerable care is taken in the design of the rest of the artificial sky.