Characterizing daylight photosensor system performance to help overcome market barriers

Despite popular enthusiasm for daylight, photosensor products have not been widely installed by building professionals due to the very poor performanc e of many products. This study means to stimulate creation of highperforman ce daylight photosensor systems that would control illumination efficiently by balancing the use of daylight and electric light and that would offer o ccupants a satisfactorily illuminated working environment in office buildin gs. Aid-rough researchers can theoretically describe the proper functioning of a daylight photosensor system, manufacturers appear not to have incorpo rated much of this theoretical knowledge. At the outset of this study, we d id not know which product characteristics in particular contributed to poor performance. We found no standard performance or technical specifications, no standard test procedure, no standard commissioning procedure, and no de tailed guidelines for commercial-building illumination applications. We identify eight commercially available daylight photosensor products for fluorescent-lamp dimming and then describe how they operate and how their o perational characteristics affect system performance (lamps, ballasts, sens or, luminaires, room geometry, and daylight.) Our innovative test method me asures the functioning of the essential components of photosensors. We pres ent data on spatial and spectral response sensitivities, and on control alg orithms. Having found technical and design weaknesses, we offer tangible su ggestions to improve future products and to ease the process of specificati on for designers.