Daylighting controls in the U.S. have fundamental design flaws that simplify installation and reduce cost but decrease reliability.This unreliable performance is a significant barrier to its widespread and satisfactory use in buildings. Daylight from sidelight windows produces an illuminance pattern that changes with time of day and season, while fluorescent top lightingproduces a predictable pattern.The simple control system is unable to adjust for these differences in lightingpatterns so interior illuminance levels are often
too low.To avoid occupant complaints, facility managers will decrease the sensitivity of photoelectric sensors so that the electric lighting is dimmed very conservatively, but this adjustment can severely undermine the energy-efficiency of the system.

Technological solution: The performance of closed-loop proportional control systems can be improved substantially at no added cost by using existing information from the control system to separate the electric lighting illumination contribution from the daylight contribution.This solution was tested at full-scale for over a year and was found to perform very well. Monitored workplane illuminance levels did not fall below 90% of the design level for 90% of the year, and when it did, the discrepancy occurred only an average of 13 minutes per day within a 12-hour day. Market adoption of our refinements will need a solid commitment from U.S. manufacturers to redesign their systems.

Commissioning solution: Past daylighting controls research has been devoted to control improvements such as photosensor design and placement to reduce the occurrence of insufficient illuminance.