This post was written by Keith Dawson for UBM Tech’s community Web site All LED Lighting, sponsored by Philips Lumileds. It is archived here for informational purposes only because the All LED Lighting site may go dark at any time. This material is Copyright 2013-2015 by UBM Americas.


Lighting for Pedestrians

A new DOE Gateway report examines the complexities of lighting for pedestrian walkways. People generally prefer lower illuminance levels, less optical punch, and a CCT below 3000K.

The US Department of Energy's Energy Efficiency and Renewable Energy program has come out with a new report on a Gateway Demonstration Program titled "Pedestrian-Friendly Outdoor Lighting." It could serve as a starting point for any community looking to improve nighttime lighting in pedestrian areas.

The report is based on projects at Stanford University and at Chautauqua Institution in New York State. Both demonstration areas are pedestrian-centric. In both areas, multiple LED and legacy light fixtures were tested, and local pedestrians were interviewed about the utility and pleasantness of the light produced.

Noting that most studies of nighttime outdoor lighting have focused on the needs of vehicle drivers, the report presents this as a top-level conclusion: "Pedestrians may have different criteria and priorities than drivers, especially in areas where cars are subordinate to bicycles and users on foot."

Glare emerged as a central problem to overcome in designing pedestrian lighting. People preferred lighting in which luminaires' angular variations in luminance were softened by diffusers; and they preferred lighting that resulted in soft-edged patterns on the ground, as opposed to the hard boundaries often sought in street-lighting scenarios.

The problem of glare contains subtleties that may not be immediately evident. Studies of streetlight glare affecting car drivers make three assumptions that aren't necessarily valid for pedestrians. First, the angle of light from a pole that causes a glare problem for a driver is assumed to be from about 75 degrees to 90 degrees (the roofline cuts off the glare at smaller angles). For pedestrians, glare can occur at angles from 0 degrees to 75 degrees (see figure). Second, there is an assumption that a driver in a relatively fast-moving vehicle won't be subjected to glare for long. Pedestrians, moving slower, will have longer exposure. Third, studies of glare, and metrics that resulted from them (such as Visual Comfort Probability and Unified Glare Rating), have assumed that only light in the direct line of sight causes discomfort or reduced ability to see. However, recent glare research has indicated that people can experience discomfort from luminance up 85 degrees above the line of sight (again, not a problem in vehicles).

Color temperature
People mostly preferred warmer color temperatures for pedestrian areas, possibly because of the familiar nature of incandescent and sodium lighting. A CCT of 2700K was the most popular option.

Illuminance level
One result of the study may be somewhat surprising to lighting designers: People prefer pedestrian lighting at much lower levels than they usually deployed, near the lower end of IES guidelines on luminance and illuminance. If glare is sufficiently controlled, lower levels of illumination can actually result in better nighttime discrimination of faces and figures away from direct light sources. The Dark Sky Association will surely welcome this finding.

This DOE Gateway research demonstrates that lighting pedestrian walkways is an extremely variable proposition, for which no single solution can be identified. The approach of multiple trials guided by local users' feedback proved to work well in identifying an optimal solution for each of the two locations studied. (The report includes the survey questions and protocols in an appendix.) Pedestrian lighting is qualitatively different than street lighting and needs to be informed by different metrics.

— Keith Dawson Circle me on Google+ Follow me on Twitter Visit my LinkedIn page, Editor-in-Chief, All LED Lighting