Peripheral detection while driving under a mesopic light level

Recent laboratory studies showed that off-axis detection in a simulated driving context is better for MH lamps than for HPS lamps at mesopic light levels. Two field studies were carried out to extend the basic findings to actual driving situations including the effect of forward headlights and oncoming headlight glare on driver performance. Both field studies used a closed track in a paved parking lot and five temporary 12 ft street luminaires to illuminate the track using MH or HPS lamps. A computer-controlled apparatus synchronized off-axis target presentations with a car moving and recorded subjects' reaction times. The first field study addressed questions of how illumination from a forward headlight system assists driver detection of off-axis targets for roadway illuminated by fixed light. Each of eight subjects detected the off-axis targets while driving a car along a straight driving lane in the track at a speed of 20 miles per hour; their reaction times were measured. The results supported the previous laboratory studies and suggested that drivers performed better under MH than HPS fixed Fight. The results also suggested that these particular forward headlights rarely improved off-axis detection. The second field study investigated how oncoming headlights impair off-axis detection. Eight subjects detected off-axis targets in a stationary car. The study again supported the laboratory studies and suggested that the glare from one type of oncoming headlights could reduce driver performance.