Quantitative comparisons of factors influencing the performance of low-beam headlamps

Abstract

This study compared the quantitative influence of a variety of factors on the performance of low-beam headlamps. The following factors were included: vertical aim, horizontal aim, mounting height, lateral separation, lens dirt, lamp voltage, number of functioning lamps (two vs. one), vehicle type (cars vs. light trucks and vans), beam pattern (U.S. vs. European), and light source (an unshielded 9007 vs. a shielded H4). The following aspects of headlamp performance were considered: visibility of pedestrians, visibility of road delineation, visibility of vehicle reflex reflectors, visibility of retroreflective traffic signs, visibility of targets near the road expansion point, glare directed towards oncoming drivers, glare reflected from wet pavement towards oncoming drivers, glare directed towards rearview mirrors of preceding vehicles, and foreground illumination. A market-weighted U.S. beam pattern, with lamps mounted at market-weighted locations, formed the basis for most of the analyses. The results indicate that from among the factors studied, vertical aim is overwhelmingly the most important factor in influencing the performance of low-beam headlamps. The second most important factor is the number of functioning lamps. The main implication of this study is that major improvements in current (fixed as opposed to adaptive) low-beam headlighting could be achieved primarily by better control of vertical aim and by longer-life headlamps.