Improving the Performance of Photo-Electrically Controlled Lighting Systems
F. Rubinstein, G. Ward and R. Verderber. Presented at the Illuminating Engineering Society Annual Conference, Minneapolis, MN, August 7-11, 1988Review by Scott Schuetter, Energy Center of Wisconsin:
Rubinstein et al. analyze three different algorithms for dimming electric lights in response to changing daylight availability. The three basic components of a photo-electrically controlled light system are described: a photosensor for measuring the illuminance at the working plane, a controller for processing the produced signal, and a dimming unit for varying the amount of electric light provided. The analyzed algorithms include:
- Integral Reset: adjusts dimming level such that the measured illuminance is kept at a constant level. This algorithm requires a "night-time calibration"
- Open-Loop Proportional: photosensor detects on daylight and the control provides a linear relationship between the available daylight and the dimming level. This algorithm requires a "daytime calibration"
- Closed-Loop Proportional: photosensor detects both daylight and electric light and the control produces a linear function of the difference between the available light and a night-time calibration level. This algorithm requires both "night-time calibration" and "daytime calibration"
The different algorithms were then tested in scale models to determine their accuracy in controlling the illuminance level on the workplane to a set level. Different room shapes, window geometries, glass transmittance, and exterior shading devices were introduced. The closed-loop proportional control performed best. This was particularly true when it had a large field of view that did not include the window. Of the other two algorithms, the open-loop proportional control outperformed the integral reset control.