The use of parking and auxiliary lamps for traffic sign illumination

Problem: In 1997, the U.S. government 'introduced an option of having headl amps labeled as visually/optically aimable (VOA). To be so labeled, the ver tical gradient of the light output needs to meet certain minimum requiremen ts. A concern with VOA lamps is that they might provide less light above th e horizontal than conventional U.S. lamps, thus reducing the effectiveness of retroreflective traffic signs. Method: This study examined 36 first-gene ration VOA lamps to assess the reduction of light above the horizontal. Fur thermore, this study addressed the possibility of maintaining the status qu o of light for sign visibility by supplementing light from VOA lamps with l ight from either parking lamps or an auxiliary lamp mounted just above the driver. Results: The results indicate that parking lamps are too weak to be able to make up for the deficit. A lamp mounted on the roof just above the driver would provide a substantial advantage over headlamps in terms of re troreflective geometry because the observation angles for such a lamp are s maller than for either headlamp. However, even taking into account this adv antage, a single such lamp would need to have peak intensity between 1500 a nd 2000 ed to make up for the deficit created by a pair of VOA headlamps. I mpact on industry: The present findings imply that neither parking lamps no r auxiliary lamps mounted just above the driver will likely be a practical solution for the reduced light output above the horizontal from VOA lamps. (C) 2001 National Safety Council and Elsevier Science Ltd. All rights reser ved.