Despite popular enthusiasm for daylight, photosensor products have not been widely installed by building professionals due to the very poor performance of many products. This study means to stimulate creation of highperformance daylight photosensor systems that would control illumination efficiently by balancing the use of daylight and electric light and that would offer occupants a satisfactorily illuminated working environment in office buildings. Aid-rough researchers can theoretically describe the proper functioning of a daylight photosensor system, manufacturers appear not to have incorporated much of this theoretical knowledge. At the outset of this study, we did 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 detailed 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 operational characteristics affect system performance (lamps, ballasts, sensor, luminaires, room geometry, and daylight.) Our innovative test method measures the functioning of the essential components of photosensors. We present data on spatial and spectral response sensitivities, and on control algorithms. Having found technical and design weaknesses, we offer tangible suggestions to improve future products and to ease the process of specification for designers.
