The U.S. Department of Energy's GATEWAY program has released a report describing four exterior SSL projects that have been completed at Princeton University, which has long recognized SSL’s potential benefits. These projects show how the school’s approach to solid-state lighting has evolved as its knowledge has broadened and as the products available have improved in performance and sophistication:

 •Replacing seven high-pressure sodium (HPS) luminaires with LED luminaires along a pedestrian walkway in 2008 allowed the school to test the new LED technology in a small-scale installation, and showed that substantial energy savings without compromising perceived visibility were possible with LED luminaires.

•Replacing 68 HPS luminaires with LED luminaires in four adjacent parking lots in 2012 showed that overall energy savings are greatly increased through the use of motion‐based dimming, and alleviated concerns that dimmed light levels might be inadequate for people approaching the lot.

•Using LED luminaires that operated night and day to replace 252 metal halide parking garage luminaires that only operated after dark showed that the inherent controllability of LEDs provides opportunities for multiple levels of control.

•Installing 41 new LED luminaires in two parking lots undergoing renovation in 2014 showed that grouping luminaires into zones by means of wireless network controls can not only save energy but also increase flexibility of control without rewiring the system.
 
For the four projects described in the report, the combined expected annual energy savings just from reduced power total 195,443 kWh, but DOE estimates that with the controls solutions that were implemented, these annual savings increase to 246,995 kWh. Through these initial projects, Princeton learned important lessons about SSL and gained experience dealing with the rapidly changing lighting landscape. Several additional exterior lighting projects have been completed at the school since those covered in the report, with a number of interior projects completed or underway.
 
For full details on the four projects, see the report.