Computer Modeling - Richard Mistrick has headed an ongoing research effort at Penn State to model photosensor-based lighting control systems in lighting analysis software. This research involves modeling all aspects of the lighting control system in detail, including the following:

• The photosensor's spatial response to incident light.
• The difference in spectral response between electric light and daylight.
• The control algorithm and variable calibration settings built into the photosensor system by the manufacturer.
• The ballast response to a control signal provided by the photosensor system.

The computer model addresses the light distribution in a room created by daylight, in addition to both the controlled and uncontrolled portions of the electric lighting system. The software determines the impact of these three sources on both the photosensor signal and work plane illuminance and computes the equilibrium point for a photosensor system at a particular calibration condition.

Previous work has shown that photosensor field of view affects a sensors ability to closely track and appropriately respond to the daylight in a space. The less light that a sensor receives directly from a daylight source, such as a window, the better the system will likely perform in tracking the daylight levels within the space. This research also showed that a closed-loop proportional control algorithm generally provided good overall system control, and determined the best conditions for system calibration to avoid undershooting the target illuminance level.

Whereas the previous work considered only unilateral sidelighting conditions, this project will expand on the previous work to address skylighting conditions and daylight from multiple sources in a single space (combinations of windows, skylights and clerestories). This work will also consider different types of lighting systems (recessed, direct indirect and completely indirect).

In previous research, direct lighting systems were shown to be easier to control. Through the detailed system modeling performed in this project, data will be obtained that describes the performance parameters necessary to provide the best possible control over a range of daylight and electric lighting systems. These parameters will include spatial sensitivity, sensor location and control algorithm sensor performance criteria.

Photosensor performance - Lawrence Berkeley National Laboratory (LBNL) has had extensive experience with researching the performance of photosensors, and were the pioneers for revealing the importance of control algorithms for optimizing photosensor performance.

Between 1984 and 1989, the Department of Energy and the Electric Power Research Institute (EPRI) funded LBNL to examine the suitability of existing photocell control systems to achieving good daylighting control. This research showed that the photocell systems at that time used a simple control algorithm that did not work well for typical daylighting applications. The paper [1] showed that the conventional control algorithm (constant setpoint) caused total light levels to undershoot the desired level under most typical applications.

The paper went on to present the mathematical basis for a new control algorithm (closed-loop proportional control) that could be easily incorporated into a photocell to greatly improve the performance and reliability of the daylighting system. The paper also presented circuit diagrams for all linear control algorithms (constant setpoint, closed-loop proportional and open-loop proportional control). Additional work at PGE-funded demonstration sites [2, 3] in California showed that the new algorithm did improve performance in real building applications.

View research references.