WHERE DOES THE GLARE COME FROM? A COMPREHENSIVE DISCUSSION OF SEEING AND GLARE IN THE NIGHTTIME ROADWAY ENVIRONMENT

This project was conceived as an overview of seeing and glare issues in light of recent concerns in North America regarding nighttime glare in traffic. By literature review and comparison of recent data, the paper analyzes seeing and glare performance of actual U.S. and ECE headlamps in use relative to each other and to current and proposed photometric standards. Topics include effects of operating voltage, headlamp mounting height, aiming, trends in glare intensity, overhead sign illumination, foreground illumination, light source factors, aim factors, auxiliary lighting factors, and bulb modification factors. It is shown that certain American objections to ECE low beam headlamps may merit reconsideration, that specific aspects of beam formation render headlamps more glare-stable under typical effects of age and modification, that certain aim philosophies are problematic, that the difference between regulatorily-prescribed test voltage and real-world operating voltage has ramifications for on-road glare, and that acceptable seeing ranges and reduced glare are not necessarily incompatible goals. There is comparative discussion of specific technical aspects of prevailing photometric standards. The focus is on low beam headlamps; however, there is also detailed discussion of high beam headlamps and vehicle-based devices that impact seeing and glare performance. Recommendations are given for regulatory changes and for further research.