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Problem: Conventional low beams headlamps do not provide sufficient illumination for nighttime visibility on curves., Method: This analytical study evaluated the advantages and disadvantages of several curve-lighting strategies that involve moving one or both low beams by various amounts. Two curve radii were examined for both curve directions, using representative tungsten-halogen and high-intensity discharge low-beam patterns. The dependent variable was the maximum distance of 3-lux illumination (combined from both lamps) at a plane 0.25 m above the roadway for seven lateral positions., Results: For short-radius, left and right curves, moving both lamps in parallel should substantially increase the visibility of objects in one's lane of travel, in several additional lanes of travel to the left and right, and off the road., Discussion: Because of the lateral trade-offs of advantages and disadvantages for large-radius curves, additional research is needed to better understand the desirable approach for these types of curves., Impact on Industry: Moving both lamps in parallel into the curve is recommended for small-radius curves.

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. [ABSTRACT FROM AUTHOR]

This study was designed to compare the illuminated surface areas of high-intensity discharge (HID) and tungsten halogen low-beam headlamps in the USA. A sample of 20 tungsten halogen lamps and 17 HID lamps for model year 2000 vehicles in the US was examined. The illuminated surface area was determined using a modified version of an Economic Commission for Europe (ECE) method for evaluating the illuminated surface of signalling devices. The main finding is that the HID low (passing) beams generally have smaller illuminated surface areas than do the tungsten halogen low beams. Because smaller light sources result in more discomfort glare (presumably via greater luminance), the present finding suggests that the smaller illuminated area is one reason for drivers reporting more discomfort from HID lamps. An implication is that the increased discomfort from HID lamps could be reduced by increasing their illuminated surface area. [ABSTRACT FROM AUTHOR]