Measurements indicate that headlight glare is more of a hindrance to full highway visibility than previously recognized. Because of the changeableness of eye sensitivity, the inadequacy of meeting visibility can escape detection unless there is a standard of measure. Tests were conducted to measure separately the adaptation level of the eyes when exposed to the roadway illuminated by sealed beam (up beam) headlights and then when exposed to the glare of various candle powers. A candle power value of the glare source was found which causes the same adaptation level as does the headlighted roadway. Computations indicate that meeting visibility up to 80 percent of open road visibility can be attained if the opposing glare is not more than 20 candle power. By comparison, the glare from present headlights may reach 800 to 1,000 candle power even with the beams tilted down. The measurements of visibility reported are based on the premise that the driver needs to see as well when meeting other cars as when driving alone in the open road. It is concluded that research towards safe headlighting is indicated. /Author/
Abstract