Increased utilization of daylighting in commercial buildings is one method of reducing the requirement forsdaytime lighting energy and for moderating peak demand. For daylight to efficiently supply some portion ofsthe design light level at the task, the electric lighting system should be photo-electrically controlled so that itsresponds (dims) in proportion to the amount of available daylight entering the building space. The locationsand spatial response of the photosensor that controls the electric lighting system must be chosen so that thesphotosensors output is approximately proportional to the illumination at the task surface. Furthermore, thessystems control algorithm, which relates the photosensor signal to the output of the electric lights, should besselected to properly account for the location of the control photosensor relative to the task and the sources ofsillumination within the controlled space. If the above considerations are not properly accounted for, then thesillumination at the task will deviate significantly from the design level (Rubinstein 1984) and the occupantssmay respond negatively, especially if the control system supplies less than the design light level.

The paper describes experimental work done to analyze how the control algorithm and the photosensorsslocation and spatial response affect the ability of a daylight-following lighting system to maintain a constantslight level at the task by responding to changes in daylight levels.