Exclusive | Fudan and Philips join forces to research LED glare issues

　　In recent years, with the rapid development of LED light sources in road lighting applications, the issue of uncomfortable glare caused by LED street lights to drivers and pedestrians has attracted increasing attention. In many areas, drivers at night repeatedly suffer from reduced night vision caused by sudden changes in street light brightness, reducing the driving safety benefits provided by street lights, especially the widespread installation of newly popular high-efficiency energy-saving LED street lights seems to make matters worse.

　　A group of researchers from China and the Netherlands has developed a method to assess the impact of uncomfortable glare caused by LED roads on people, creating a model that can evaluate the level of driver discomfort under various lighting conditions. The team of researchers comes from Fudan University, Philips Research Asia (Shanghai, China), the Human Technology Interaction Group, Eindhoven University of Technology, and Philips Research Laboratories (Eindhoven, the Netherlands).

　　Discomfort glare is notoriously difficult to characterize. Glare research conducted by Fudan University in Shanghai, China, and Eindhoven University of Technology focuses on finding the key factors that cause discomfort glare, leading people to need to look away from a light source. The research group established a laboratory simulating street light working scenarios, allowing volunteers to observe simulated 72 different lighting conditions. Lin Yandan, associate professor at Fudan University, said: "With the development of the LED industry, undoubtedly, more and more LED lights will be used for road lighting. We believe there is an urgent need in the lighting industry to update the way of characterizing the discomfort glare caused by LED road lights."

Experimental road for LED street light glare testing (Image source: Lin Yandan)

　　LED street lights are smaller and bluer than traditional street lights

　　Lin Yandan stated that the traditional standards and methods for evaluating discomfort glare are still based on the properties of traditional light sources and may not be suitable for LED street lights. For example, LEDs of the same brightness are smaller than traditional street lights, which may increase discomfort glare. In addition, typical white LED spectra have more energy in the blue portion, which may also cause more glare, because, according to previous research, at the same brightness, the human eye perceives blue light as brighter.

　　In the investigation, the team designed a laboratory setup to simulate road lighting conditions under different conditions. The researchers painted the floor and walls of a room completely black and placed different light sources around the room to simulate the lighting conditions of LED street lights on dark roads. The researchers adjusted the light sources to create 72 different lighting conditions, and volunteer observers were asked to define the level of discomfort glare on a 9-level scale, ranging from "imperceptible" to "unbearable".

　　The test also has some benchmarks from previous glare testing research. Lin Yandan said: "Although the discomfort glare characteristics of traditional light sources may not necessarily apply to LED lights, the factors affecting comfortable glare may remain unchanged." The researchers systematically modified four experimental lighting parameters: the brightness of LED lighting, background brightness, the apparent size of the LED light from the observer's perspective, and the angle between the LED and the observer's line of sight.

The above laboratory work results verify road lighting

Based on these results, the research group developed a model, which they verified with two additional experiments—one conducted in the laboratory and one on a real road. The researchers found that the interaction between LED luminance and solid angle is the most significant factor affecting discomfort glare. To minimize uncomfortable visual experiences, they recommended reducing the amount of light hitting the eyeball and the luminance contrast between the street light and the background. These can be achieved through well-designed LED lighting unit optics and carefully arranged luminance contrast between street lights.

The project will continue with follow-up work, hoping to guide industry standards. The researchers hope their model can be used by LED street light designers and construction companies. Looking ahead, the team plans interdisciplinary research on the physiological changes caused by glare, such as eye movement and pupil size research, which can deepen the 9-point glare measurement scale.

Reference:

Lin Yandan et al., Optics Express (2014); http://dx.doi.org/10.1364/OE.22.018056