Mercury-free HID headlamps: glare and colour 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 colour 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 nine mercury-free light sources with the chromaticities of 17 traditional HID light sources. Similarly, 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 mercury-free light sources with the chromaticities of the same materials when illuminated by the traditional HID light sources. The main findings are: (1) The discomfort glare from the mercury-free HIDs is predicted to be comparable to that from the 'bluest' of the traditional HIDs. (2) Colour 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 coloured retroreflective materials. [ABSTRACT FROM AUTHOR]