Sky luminance mapping for computational daylight modeling

Building design and control applications can benefit from daylight simulation. Currently, most daylight simulation applications work with simplified sky luminance models. However, reliable prediction of daylight availability in indoor environments via computational simulation requires  reasonably detailed and accurate sky luminance models. As past research has demonstrated, relatively low- cost sky luminance mapping via digital imaging can provide an alternative to high-end research-level sky scanners and thus support the provision of information on sky luminance distribution patterns on a more pervasive basis. This paper explores the potential of using a digital camera with a fish-eye converter toward real-time derivation of sky luminance distribution maps. To explore the feasibility of this approach, sky luminance data derived from digital images were compared to the corresponding photometric measurements. To further calibrate the process, a correction factor was applied to the digitally gained luminance values. This correction factor was derived as the ratio of the optically measured to the digitally derived horizontal illuminance levels due to the sky dome. The results show that digital sky imaging calibrated with parallel measurements of overall horizontal illuminance levels can provide a reliable basis for the generation of sky models for daylight prediction tools. Thus, the reliability of daylight simulation may be increased and simulation-based daylight- responsive   lighting   systems   control   methods   in buildings  can be enhanced.