The Lighting Research Center (LRC) at Rensselaer Polytechnic Institute has published a new guide for parking lot lighting, which demonstrates how to promote safety while reducing power demand by lighting the parking lot area more uniformly.
“Exterior lighting in parking lots should support the visibility of hazards—and reinforce perceptions of safety so that people are not afraid to use the space at night,” said Jennifer Brons, Director of Design Demonstrations, who was one of the guide's authors.
The guide provides a summary of research results on this topic, along with four steps that lighting designers and specifiers can follow in order to compare performance of alternatives to a base case parking lot lighting design.
Average light levels are important contributors to perceptions of safety in parking lots. But to minimize power demand, lighting designers and specifiers should strive to maximize uniformity. While sources with higher correlated color temperature (CCT) will be perceived as brighter than low CCT sources, this is limited in importance compared to uniformity. With better uniformity, much lower average illuminances can be provided while improving both perceived safety and brightness. The guide also provides a link to a calculation tool specifiers can use to estimate occupants’ ratings of perceived safety.
“By using perceived safety as a performance criterion, alternate lighting designs can be evaluated to minimize power demand while balancing other design criteria,” said John Bullough, Director of Transportation and Safety Lighting Programs. “Taking advantage of uniformity has implications not only for energy savings but also for minimizing light pollution.”
Support for this research was provided by Natural Resources Canada and other members of the Lighting Energy Alliance, including Efficiency Vermont, Energize Connecticut, National Grid, Northwest Energy Efficiency Alliance, and ComEd.