A team of researchers from China and the Netherlands has developed a way to evaluate the human impact of uncomfortable glare caused by LED road lights. The group, led by Yandan Lin, an associate professor and director of the Vision and Color Research Laboratory at Fudan University in Shanghai, China, created a model that can predict the level of discomfort experienced by drivers under various lighting conditions. Their findings, which could guide streetlight placement and design, were reported in The Optical Society's (OSA) open-access journal Optics Express .
"With the development of the LED industry, there is no doubt that more and more LED lights will be used for road lighting," said Lin. "We believe that the lighting industry has an urgent need to update the ways to characterize discomfort glare caused by LED road lights."
LEDs emit the same amount of light as conventional bulbs from a smaller area, which could increase the discomfort glare, and white LEDs typically have more energy in the blue part of spectrum, which can also cause more glare because blue light is perceived brighter by the human eye under the same light levels, based on past studies.
To investigate the effect of LED streetlights on the discomfort glare perceived by drivers, the team devised a laboratory set-up to mimic visual conditions on the road. The researchers painted the floors and walls of a room completely black, and then positioned a collection of light sources around the room to simulate the illumination from an LED streetlamp as it would appear to a driver on a dark road. The researchers adjusted the light sources to create 72 different lighting conditions, and volunteer observers were asked to rate their level of discomfort glare under each condition on a standard deBoer 9-point rating scale, ranging from "unnoticeable" to "unbearable."
Lin and her colleagues systematically modified four lighting parameters in their experiments: the luminance or intensity of light in a given area, the background luminance, the apparent size of the LED lights from the perspective of the observers and the angle between the LEDs (called the solid angle) and the line of sight of the observers.
Based on the results, the team developed a model that related these four parameters to the level of discomfort glare experienced by an observer. They validated the model with two additional experiments – one carried out in the lab and one on real roads.
The researchers found that the interaction between the LED luminance and the solid angle, which can be characterized by the amount of light hitting an observer's eyes (known as vertical illuminance) was the most significant factor affecting discomfort glare. To minimize discomfort, they recommend minimizing both the amount of light hitting at the eyes and the luminance contrast between the streetlights and the background, which can be accomplished through good optical design of the LED light unit and careful placement of each streetlight.
Read the release on the report, via Eurekalert: Improving driver safety: How to prevent streetlight glare in the new world of LED lighting