Low-beam headlamps: Effects of realistic levels of dirt on light output

Abstract

This study evaluated changes in the light output of low-beam headlamps as a function of dirt accumulated during a 482 km route, representing a 10-day amount of driving for a typical United States driver. The complete route was traversed on three separate occasions, under each of the following environmental conditions: summer while dry, summer while wet, and winter with road salt. Candela matrices were obtained for a rectangular central portion of the beam, extending from 20 degrees left to 20 degrees right, and from 5 degrees down to 5 degrees up (in 0.5 degrees steps). Photometry for each of two lamps was performed twice after the completion of each drive, first 'as is' and then after cleaning. The results indicate that dirt deposits tended to cause the light output to decrease below horizontal and increase near and above horizontal. The changes in the light output differed between the driver-side and passenger-side lamps, especially after the two summer drives. The largest changes occurred after the winter drive, with the decreases and increases in a large part of the beam for both lamps exceeding 25%, and with some of the increases exceeding 50%. At the United States, European and Japanese test points that control road illumination, the dirt effects tended to reduce the light output, and some of these decrements exceeded 25%. On the other hand, at test points that control glare, the dirt effects tended to increase illumination, but none of these increases exceeded 25%. (A)