The Effect of Control Algorithm Photosensor Response on the Performance of Daylight Linked Lighting Systems

Increased utilization of daylighting in commercial buildings is one method of reducing the requirement for daytime lighting energy and for moderating peak demand. For daylight to efficiently supply some portion of the design light level at the task, the electric lighting system should be photo-electrically controlled so that it responds (dims) in proportion to the amount of available daylight entering the building space. The location and spatial response of the photosensor that controls the electric lighting system must be chosen so that the photosensors output is approximately proportional to the illumination at the task surface. Furthermore, the systems control algorithm, which relates the photosensor signal to the output of the electric lights, should be selected to properly account for the location of the control photosensor relative to the task and the sources of illumination within the controlled space. If the above considerations are not properly accounted for, then the illumination at the task will deviate significantly from the design level (Rubinstein 1984) and the occupants may 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 photosensors location and spatial response affect the ability of a daylight-following lighting system to maintain a constant light level at the task by responding to changes in daylight levels.