The U.S. Department of Energy’s Gateway Report series is one of the more interesting efforts to provide a reality check on applications of new lighting technologies. DOE’s most recent release, “Pedestrian Friendly Outdoor Lighting” (PDF) reports on a study of two projects in which lighting was used to illuminate areas for walking.
The report points out that parameters for most outdoor lighting is oriented toward the needs of vehicle traffic more than foot traffic. In this study, DOE followed two pedestrian-focused projects at sites where the pedestrian-scale lighting needed improvement: Stanford University in California and the Chautauqua Institution in upstate New York. The results from these projects reveal that pedestrians may have different criteria and priorities than drivers, especially in areas where cars are subordinate to bicycles and users on foot.
The report looks at a variety of factors that affect pedestrian comfort with the lighting, ranging from safety from tripping, slipping and falling to personal security from harm or intimidation to unwanted light in residential windows.
Some of the findings the DOE reports include that pedestrians cared about the daytime appearance of the luminaire; they found glare to be a significant factor and preferred soft-edged patterns of light on the ground with warm light colors (2700K to 3000K) and were fine with illuminance at the low end of the levels recommended by the Illuminating Engineering Society (IES) recommendations so long as glare was reduced.
Pedestrians found diffused light more acceptable even if measures of spot illuminance were high, meaning even with well-balanced LED arrays and clear metal-halide tubes the use of frosted refractors and flat panels improved walkers’ comfort levels.
DOE pointed out that applications of lighting for pedestrian spaces will always vary depending on activities and that tradeoffs will invariably have to be made. There is no glare metric that works reliably for pedestrian lighting, so full-scale mock-ups are necessary to get useful user feedback.
Not every neighborhood is suited for pedestrian-friendly approaches, but where communities are receptive, the following may help mitigate glare, improve visual comfort and visibility, and make outdoor spaces more inviting:
• lower lumen output luminaires and lower illuminances, if luminaire brightness can be controlled
• luminaires that spread luminance (“brightness”) over a larger area
• luminaires with less optical punch and less sharp angular variation in candlepower
• luminaires delivering warmer color light, usually lower than 4000K, and often below 3000K correlated color temperature.