Vertical Illuminance Uniformity for LED Road Lighting

LED road lighting has been installed in many cities and it's dominating for almost all new roads. Its advantages have been well recognized, such as improved energy efficiency, better beam control, slim design, smart control, etc. However, visual discomfort has been one of the often-heard complaints about LED road lights since very long ago. Visual discomfort can be attributed to three factors in general: disability/discomfort glare, road surface uniformity, vertical illuminance distribution. For disability/discomfort glare and road surface uniformity, there have been abundant studies and standards available for engineers and researchers to refer to. While in comparison, the vertical illuminance distribution lacks sufficient investigative efforts. Of the many factors that impact visual comfort for road lighting, vertical illuminance distribution was sometimes mentioned but only in a qualitative manner and always linked with Small Target Visibility (STV). In this study, we aimed to fully understand the role of vertical illuminance distribution in visual comfort for road lighting. The related on-site investigations, perception tests, optical simulations, as well as the posterior verifications were all carried out on the context of typical China's road configurations. As a result, an initial model has been developed in characterizing the impact of vertical illuminance distribution on visual comfort for drivers. It is believed to be a proper supplement to the existing visual comfort evaluation system.