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Mercury-Free HID headlamps: glare and color rendering

This study examined the potential effects of the spectral power distributions of mercury-free high-intensity discharge (HID) headlamps on discomfort glare for oncoming drivers and on color rendering of retroreflective traffic materials. In both cases, the effects of mercury-free HID light sources were compared to the changes in these properties that occurred when the tungsten-halogen light sources were replaced with traditional (mercury containing) HID light sources. Specifically, the effect on discomfort glare was estimated by comparing the chromaticities of 9 mercury-free headlamps with the chromaticities of 17 traditional HID headlamps. Analogously, the effects on color rendering were estimated by comparing the chromaticities of 46 retroreflective materials when illuminated by the mercury-free headlamps with the chromaticities of the same materials when illuminated by the traditional HID headlamps. The main findings are as follows: (1) The discomfort glare from the mercury-free HIDs is predicted to be comparable to that from the “bluest” of the traditional HIDs. (2) Color rendering with headlamps using the mercury-free HIDs is likely to be acceptable. (3) The use of mercury-free HIDs is unlikely to have appreciable effects on the relative brightness of colored retroreflective materials.

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