Visual Aiming of European and U.S. Low-Beam Headlamps 920814
This study evaluated the effect of the sharpness of the cutoff (the transition between the lighter and darker portions of the beam) of low-beam headlamps on visual vertical aiming. Out of ten lamps tested, seven had a U.S.-type beam pattern and three had a European-type beam pattern. Twenty younger and middle-aged subjects of both sexes, along with an experienced lamp aimer, were asked to adjust the vertical aim of the lamps in such a way that the cutoff of the beam was coincident with a horizontal line on a vertical surface. The subjects were instructed to make the alignment using the illumination gradient to the right of vertical for the U.S.-type lamps and to the left of vertical for the European-type lamps. Each person aimed each lamp ten times.
There are two main results. First, the location of the perceived cutoff was generally near the location of the maximum contrast between adjacent vertical parts of the beam pattern. Second, the variability of the aiming performance was systematically related to the magnitude of the maximum contrast.