The use of parking and auxiliary lamps for traffic sign illumination

Abstract

Problem: In 1997, the U.S. government introduced an option of having headlamps labeled as visually/optically aimable (VOA). To be so labeled, the vertical gradient of the light output needs to meet certain minimum requirements. A concern with VOA lamps is that they might provide less light above the horizontal than conventional U.S. lamps, thus reducing the effectiveness of retroreflective traffic signs. Method: This study examined 36 first-generation VOA lamps to assess the reduction of light above the horizontal. Furthermore, this study addressed the possibility of maintaining the status quo of light for sign visibility by supplementing light from VOA lamps with light 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 retroreflective geometry because the observation angles for such a lamp are smaller than for either headlamp. However, even taking into account this advantage, a single such lamp would need to have peak intensity between 1500 and 2000 cd to make up for the deficit created by a pair of VOA headlamps. Impact on industry: The present findings imply that neither parking lamps nor auxiliary lamps mounted just above the driver will likely be a practical solution for the reduced light output above the horizontal from VOA lamps.