Calculating indoor natural illuminance in overcast sky conditions

The work shows how natural illuminance values inside buildings depend on the calculation method of thesky luminance distribution implemented in the computer code which, for a room of fixed geometry andcharacteristics, transforms the outdoor meteorological data into indoor illuminance data.By means of the INLUX calculation code, experimentally validated, 12 different calculation methods of skyluminance distribution were compared, sometimes obtaining strong differences among the calculated valuesof indoor illuminance. The choice ofsomemethods instead of others depends on the meteorological dataavailable in the place considered. Comparing the calculated illuminances with the experimental valuesmeasured inside a scale model (1:5), located outdoors in Osaka (Japan), and exposed to daylight, the bestcalculation methods, among those considered, of sky luminance under overcast sky conditions wereidentified.