The Lighting Research Center (LRC) at Rensselaer Polytechnic Institute has published new guide for car park 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.
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.
“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.
In the meantime, here’s a Q&A with John Bullough:
DVN : Do you think, safety feeling is equivalent in automotive lighting with homogeneity so important ?
John Bullough : I think they have some similarities but are different perceptions. Pedestrians want to be able to see people who might try to hide in dark areas of a parking lot and they are mainly concerned with their own personal security. A driver wants to see down the road, and is less concerned about threats to their security. Both light level and uniformity matter for both perceptions but there is some evidence that drivers are more concerned with light level than with uniformity.
DVN : Do you think possible a launch of equivalent study in automotive lighting ?
John Bullough : Some of these studies have been undertaken. We presented a paper at the SAE World Congress in 2009 (paper # 2009-01-0336) describing a study for the Transportation Lighting Alliance that supports my statement about drivers mainly preferring high light levels in the foreground. Researchers from UMTRI and from industry have investigated how intensity and uniformity impact drivers’ perceptions about their lighting. Interestingly, they sometimes prefer lighting conditions such as high foreground brightness, which does not have a real safety benefit. That counterintuitive finding may be worth exploring further because it suggests that «the customer might not always be right!»