LED headlamps: glare and colour rendering

Because of rapid improvements in the light output of light-emitting diodes (LEDs), serious consideration is being given to using LEDs as light sources for headlamps. This analytical study examined the potential effects of LEDs on discomfort glare for oncoming drivers and on colour rendering of retroreflective traffic materials. In both cases, the effects of LED light sources were compared to the changes in these properties that occurred when the traditional tungsten halogen light sources were replaced with high-intensity discharge (HID) light sources. Specifically, the effect on discomfort glare was estimated by comparing the chromaticities of seven LED light sources (considered for use in headlamps) with the chromaticities of the light sources from 17 actual HID headlamps. Analogously, the effects on colour rendering were estimated by comparing the chromaticities of seven red retroreflective materials (red being the most important messenger of meaning in traffic control) when illuminated by the LED light sources with the chromaticities of the same materials when illuminated by the HID light sources. Based on our analyses, headlamps using the currently considered range of LEDs are predicted to result in: 1) more discomfort glare than the current HID headlamps, and substantially more discomfort than tungsten halogen headlamps; 2) acceptable colour rendering; and 3) no appreciable effects on the relative brightness of red retroreflective materials.