The Potential Impact of Automotive Headlight Changes on the Visibility of Reflectorized Highway Signs

Except for changing to halogen sources, increased high-beam candlepower, and styling, no drastic changes have been made to U.S. headlamps for almost 20 years. During the past 2 years, however, many basic modifications have been made to headlamps and more changes, both mechanical and optical, are expected. All non-illuminated road signs require a relatively snail quantity of upward headlamp illumination to be visible. Unfortunately, this very same light contributes to the glare experienced by oncoming drivers. Many European designs have sharply reduced this upward component, a design change which could also take place in the U.S. under current SAE standards. The paper develops lighting intensity values required for minimum overhead sign visibility, reviews the performance of current sealed-beam and European headlamps, and suggests some changes to SAE Standard J 579c to assure the continued usefulness of these signs.