The U.S. Department of Energy published a GATEWAY report detailing the results of several LED lighting installations at Princeton University. As part of Princeton University’s sustainability plan that it launched in 2008, the University first installed an LED-based exterior lighting system that year. Princeton installed the first exterior LED on the campus along a pedestrian walkway. The University replaced seven high-pressure sodium lights with LED Luminaires along the walkway that runs alongside a major campus roadway and connects perimeter parking areas with the central campus. This upgrade alone reduced the wattage and energy use for lighting that walkway by more than 60%, saving about 2500 kWh annually. Also, the school’s facilities group received anecdotal reports that more students were now using the walkway because it felt safer than when it was under HPS lighting.
Subsequently, the University has conducted some small scale interior light replacement projects. Then, Princeton committed to a more extensive exterior LED lighting installation. In 2008, 480V LED drivers that matched the school’s 480V electrical distribution system were not available. A transformer was added at each luminaire. Since then, 480 V drivers have become available. Additionally, several LED luminaires on the Elm Drive walkway failed early due to electrical surges. Now, surge suppression is integral to LED luminaires used at the school.
The school has learned from the first installation. Also, new products have come out to make the LED lighting more reliable and able to cover more applications. For example, 480V LED drivers to match the school’s 480V electrical distribution system were not available in 2008, so a transformer was added at each luminaire. Since that time, 480V drivers for LED light sources have been introduced. In addition, several of the LED luminaires on Elm Drive experienced early failure due to electrical surges. However, surge suppression is now integral to the LED luminaires used at the school.
In Mid 2012 Princeton completed its first LED-based parking lot lighting installation that replaced 68 HPS lights with LED luminaires in four adjacent lots in the southwest area of the campus. The parking lot installation resulted in 64% energy savings. The University got further savings from the bi-level control based on motion detection. The project demonstrated that motion-detection-based dimming greatly increased energy savings.
The initial parking lot installation led Princeton facility engineers to seek ways of networking their parking-area lighting systems into zones rather than having them depending on individual controls—even though the school received no complaints related to this functionality.
The incumbent lighting in Princeton’s West Parking Garage combined 252 metal halide (MH) luminaires that operated after dark with fluorescent luminaires that operated during daylight hours. In early 2013, the school replaced 252 metal halide (MH) fixtures in the West Parking Garage with LED luminaires. The output of the LED luminaires was set to 90% of the maximum, with the idea that this could be increased over time as the light output depreciates. With the reduction in power consumption from nighttime operation alone, the LED system saves 66% or more than 143,000 kWh annually. The school achieved additional savings through the use of controls. Each LED luminaire has an integrated motion detector and daylight sensor, with output dimmed to 50% of maximum whenever daylight is present and to 20% of maximum when there is no movement nearby. The additional savings at night from these controls is estimated at 40,000 kWh annually.
The parking garage project showed Princeton that LED lighting offers opportunities for multiple levels of control during daytime and nighttime hours. The controls can allow a single LED system to replace two different incumbent systems.
The University found that a while mounting the LED luminaires between the concrete beams helps reduce glare for approaching drivers, the beams can interfere with the motion detectors, so there was a trade-off.
In Early 2014, two Princeton parking lots got 41 new LED luminaires as part of a major renovation to those areas. Because this was a new installation, the LED luminaires did not replace existing HPS luminaires. However, the LED luminaires saved more than 60% of the energy that would have been used by a conventional HPS system. The controls provided additional savings. Each LED luminaire has an integrated photocontrol and motion detector. Instead of individual control, the luminaires are grouped into zones using a wireless network. The grouping allows an area of the parking lot to dim to 20% whenever no motion is detected within an area. Detected motion from any one of the sensors in a zone brings the luminaires in the area to full output. The report noted that this effect can increase the perceived safety in the parking lot.
The wireless network control also enabled Princeton to implement a programmed weekly schedule and to override the motion-detection system when desired. However, system overrides during special events still must be manually controlled. Princeton is working with the vendors involved to make this functionality easier to implement in the future.
The SSL lighting projects at Princeton have lead to substantial energy savings and valuable experience. 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.
The University has completed several other LED-based exterior lighting projects since those covered in the GATEWAY report. Additionally, some small and large interior SSL projects have been completed at Princeton or are now underway—including replacing a compact-fluorescent system with LEDs in the Dillon Gymnasium, and a major LED retrofit at the Carl Icahn Laboratory.