“The dual-loop strategy resolves certain issues that, until now, limited daylight harvesting,” says CLTC Co-director Dr. Konstantinos Papamichael. “It combines the advantages of closed-loop and open-loop strategies while eliminating the disadvantages of each.” The LMLS-600 also features two highly accurate silicon photodiodes that mimic the human eye’s photopic response. The end result is better control of electric lighting, as well as greater energy and cost savings.
CLTC monitored a demonstration of the dual-loop control system at Walmart’s 24-hour West Sacramento store for a full year. Energy savings measured 36 percent, on average, compared to 24 percent from an open-loop control system. This 50 percent improvement in efficiency reduced annual lighting energy use by 113.5 MWh and saved $14,500 in electricity costs. Closed-loop photo sensors do not always respond well when there are changes within a space.
Such changes can occur, for example, when a retail store updates its displays, placing items of different colors, shapes and reflective finishes underneath skylights and sensors. Open-loop photosensors resolve this issue, but they do not always correspond with ambient light levels in the space, especially at the beginning and end of the day, and during partly cloudy conditions. This can result in distracting light-level changes.
The dual-loop photosensor is the newest component in WattStopper’s Digital Lighting Management (DLM) system. Following an automatic setup process, it works with DLM room controllers to deliver automatic on/off switching, step dimming or continuous dimming. The LMLS-600 also recalibrates itself automatically, so it constantly adapts to interior space changes, as well as lamp lumen depreciation and changes in daylight contribution, without the expense of manual maintenance.
The dual-loop control technology is expected to achieve wide consumer acceptance and yield high energy savings, especially in California, where building energy codes will soon require electric lighting controls in the majority of commercial spaces with skylights.