A review and analysis of parallel goniophotometry
A reliable computer simulation of natural and artificial lighting of an indoor environment requires the thorough knowledge of the angular intensity distribution of light scattered or emitted by the various objects involved such as the illuminated surfaces, the trans-illuminated windows or fenestration systems, as well as the luminaires. The angular intensity distribution of light flux reflected, transmitted or emitted as a function of the illumination angle can be measured with an instrument called goniophotometer. Fast measurement, essential in most practical applications, requires the simultaneous detection of all scattering directions with a so-called parallel goniophotometer. In this paper we define and explain the three working principles on which a parallel goniophotometer can rest, namely (i) screen imaging, (ii) dioptric angular mapping, and (iii) catadioptric angular mapping. We provide a state-of-the-art of these instruments and compare their performance and limitations based on a few key parameters.