The goal of this study was to examine whether the recent changes in the sharpness of the vertical gradient in U.S. low beams have changed the importance of headlamp levelling and cleaning systems. The study consisted of three parts. In the first part, we collected new data on dynamic distributions of pitch angles for a passenger car, a minivan, and an SUV in actual traffic. In the second part, we applied the new dynamic pitch data (combined with recent static pitch data) to representative low-beam patterns to estimate the changes in the benefits of levelling systems. These estimates were made for a comprehensive combination of static and dynamic sources of misaim; additional analyses would be necessary to determine the relative benefits of levelling systems that address selected sources of misaim. Three sets of photometric data were used in the analysis: market-weighted 1997 and 2004 tungsten-halogen beam patterns, and a representative 2004 HID beam pattern. In the third part, we applied a previously derived model for the effects of dirt on the three beam patterns to estimate the changes in the benefits of cleaning systems. In both sets of analyses, the effects on both visibility and glare were considered. The results indicate that (1) the importance of headlamp levelling systems for U.S. low beams has recently increased substantially for tungsten-halogen and especially HID lamps, and (2) the importance of headlamp cleaning systems has stayed approximately the same. (Author/publisher)
Abstract