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This simulation study examined the effects of proportional increases in light output throughout the entire headlamp beam pattern on visibility. The baseline beam pattern was a median market-weighted US tungsten–halogen low-beam pattern. Ten derived beam patterns were obtained by multiplying each point in the baseline beam pattern by a constant that ranged from 1.1 to 2.0, in increments of 0.1. Finally, for comparison, we also used the median market-weighted US high-beam pattern. Visibility changes were estimated by calculating the change in the reach of a 3-lux line 0.25 m above the road surface, for both straight and curved roadways. The results indicate that substantial gains in visibility on straight roadways require an increase of about 50% in the overall light output of low beams. On curves, obtaining a substantial gain in visibility in several lateral positions would require significantly greater increase in light output. These results provide an enhanced baseline against which to compare other potential improvements in low-beam visibility, including more localized changes in static beam patterns and adaptive headlighting systems. [ABSTRACT FROM AUTHOR]

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]

This study measured direct and rearview-mirror glare illuminances produced by low-beam headlamps in a sample of 22 passenger vehicles. The glare illuminances were measured for 12 common glare situations that were defined by a full factorial combination of three scenarios (oncoming driver, center rearview mirror of a preceding driver, or driver-side mirror of a preceding driver one lane to the right), two longitudinal distances (25 m or 50 m), and two vertical locations (illuminated vehicle being either a car or a light truck/van/sport utility vehicle). The measurements were made outdoors at night on asphalt pavement. The median illuminances (not taking into account window transmittance or mirror reflectance) ranged from 0.5 lux for an oncoming driver of a light truck/van/sport utility vehicle at a distance of 50 m, to 3.4 lux at the driver-side mirror of a preceding car at 25 m one lane to the right. The ratios of the maxima and the minima measured for each of the 12 glare situations were large, ranging from about 5:1 to 36:1. The median actual illuminances were compared to the median expected illuminances based on a recent, laboratory-measured, representative sample of US low-beam patterns, taking into account the possible effects of dirt, voltage, misaim, and pavement reflectance. This analysis indicates that the actual illuminances could be very well modeled using the laboratory-measured beam patterns and assuming a linear relationship between the light output of clean and dirty headlamps. Additional analyses evaluated the relationships between headlamp mounting height and glare illuminance. [ABSTRACT FROM AUTHOR]