Design and development of a low-cost angular sky luminance measurement system

Maskarenj, Marshal [UCL] Banerjee, Rangan Ghosh, Prakash C.

Energy efficient building design requires simulated assessment of overall performance through reliable models, taking into account the daylight variations along with other significant parameters such as ventilation, plug loads and occupant behaviour. A robust indoor daylight model applicable to locations across the globe needs to incorporate local variations of sky luminance on a spatial and temporal basis, and needs an affordable system for dynamic angular daylight measurement to be used as part of a wider distributed network. In the present work, a low-cost prototype based on Light Dependent Resistors for measurement of angular daylight luminance distribution is developed and analyzed. This device was used to capture the angular analog data for 221 sky segments (20 azimuthal x 11 altitudinal segments and Zenith). The analog data was further converted to luminance data, and the visualized data was compared with sky-dome photographs and also with simulated polar daylight maps for a few Commission International de l’Eclairage (CIE) skies. The repeatability of the experiment was assessed by comparing the luminance data for selected sky segments over multiple time-segments for consecutive days. Measured data was found to be an acceptable fit with the CIE-models over various time segments, validating the prototype.