Executive Summary

The Lighting Research Center (LRC) proposes to develop a combination of an energy efficient LED streetlight and a road surface treatment that will reduce sky glow light pollution and increase visibility of objects in the road.

Streetlights are a necessary element for roadway safety, but they have a negative impact on the environment in two ways. First, they use 56 TWh/year of electricity in the U.S., resulting in 33 million metric tons of carbon dioxide emissions annually. Second, outdoor lighting causes light pollution. According to National Geographic magazine, “[M]ost of humanity lives under intersecting domes of reflected, refracted light, of scattering rays from overlit cities and suburbs, from light-flooded highways and factories.”

Commercially available LED streetlights already have the potential to reduce streetlight power demand per mile (up to 41% according to an LRC study), and as LED efficacies and light output improve, the power demand per mile is expected to improve even further. However, current LED streetlights do not reduce light pollution.

A significant portion of light pollution is caused by light reflected from the ground, not light emitted directly from outdoor luminaires. The LRC proposes to create a new streetlight system that significantly reduces light pollution by preventing its light from reflecting off of the roadway surface. This will be accomplished by harnessing the unique properties of LEDs and creating a new road surface coating. The streetlight will produce white light with a combination of red, green, and blue LEDs, which produce pure colors in a narrow wavelength bands. A road surface coating will be developed that incorporates dyes that absorb those specific wavelengths but reflect most other wavelengths. The result will be a road that reflects little light from the streetlights, but will reflect most wavelengths of sunlight during the day. At night, objects on the road will be visible because they will be illuminated with white light, but the road will appear dark. This will increase the luminance contrast between an object in the road and the roadway surface, making obstructions even more visible. Standard striping along the center and edge of the road will demarcate the roadway boundaries to drivers. Conventional headlights will illuminate the road normally. Because the roadway coating will reflect most wavelengths of sunlight, it will not add to the urban heat island effect nor contribute to global warming.

The primary deliverable for this project will be measurements of a laboratory-scale demonstration of an RGB luminaire and a coated surface to determine the reflectance of the light from the luminaire compared with standard roadway materials. The LRC will create the luminaire, identify potential dyes, and measure the photometric properties of the coatings. The LRC will partner with Passonno Paints, a paint manufacturer based in Watervliet, NY, to advise on materials and manufacturability and to fabricate sample roadway coatings.

This project was cosponsored by the Research and Innovative Technology Administration of the U.S. Department of Transportation through the University Transportation Centers program.