Princeton University, Princeton, N.J., embarked in 2008 on a sustainability initiative that included extensive replacement of exterior lighting on the school’s campus. The school installed its first LED exterior lighting system that year, hoping to learn more about the technology and further its development. The U.S. Department of Energy recently released one of its Gateway reports profiling four exterior SSL projects that have been completed at Princeton since 2008.
Princeton’s first LED exterior lighting project was to replace seven high-pressure sodium (HPS) luminaires with LED luminaires along a pedestrian walkway that runs alongside a major campus roadway and connects perimeter parking areas with the central campus and several athletic fields. The upgrade reduced the wattage and energy use by more than 60%, saving about 2500 kWh annually. “What’s more, the school’s facilities group received anecdotal reports that more students were now using the walkway because it felt safer than before,” the DOE report said.
This early project allowed Princeton to test the new LED technology in a small-scale, real-world installation. Among the early lessons, the school grappled with finding 480V LED drivers to match the school’s electrical distribution system, though drivers designed for 480V operation have since become available and have been used in subsequent installations, and several of the LED luminaires used in that early installation experienced early failure due to electrical surges, so surge suppression is now integral in the LED luminaires used at the school.
Subsequent exterior lighting projects profiled in the DOE report showed greater benefits with the improvement of LED lighting and control technology over time. A parking lot relighting project finished in 2012 replaced 68 HPS luminaires with LED luminaires in four adjacent lots using an integral passive infrared motion detector that dims to 20% when no motion is detected for a period of time. The project delivered 64% energy savings from the LED luminaires, with further savings from the bi-level control.
The relighting of Princeton’s West Parking Garage in 2013 replaced 252 metal halide (MH) luminaires that operated after dark and fluorescent luminaires that operated during daylight hours. The MH luminaires were replaced one-for-one with LED luminaires that provided lighting both during the day and at night. The LED system saves more than 143,000 kWh annually plus additional savings from the controls estimated at 40,000 kWh annually.
The fourth project, completed in 2014, was a new construction installation of 41 new LED luminaires in two Princeton parking lots as part of a major renovation to those areas. In this case, each LED luminaire has an integral photocontrol and motion detector, and the luminaires are grouped into zones using a wireless network.
“From both an economic and a carbon-reduction standpoint, the SSL experiences at Princeton have been highly successful and informative,” the DOE report concluded. “By incorporating different types of controls into its early projects, Princeton gained valuable experience in extending the energy savings made possible by SSL efficiency. For the four exterior SSL projects described in the GATEWAY report, the expected annual energy savings just from the reduced power totals 195,443 kWh, but DOE estimates that with the controls solutions that were implemented, these annual savings actually could increase to 246,995 kWh.”