The Effect of Running Lights on Vehicle Conspicuity in Daylight and Twilight

Abstract

Three field experiments were set up to investigate the conspicuity afforded approaching vehicles by running lights of different intensities under various levels of ambient daylight illumination. The main criterion of conspicuity used was the distance at which vehicles appearing in the periphery of the visual field could be detected (Peripherical Detection Distance). A second criterion used was subjectively reported, relative conspicuity, between pairs of vehicles viewed directly, (Subjective Central Conspicuity).

In the first experiment, peripheral detection distances were measured in full daylight for vehicles approaching at visual angles of 30° and 60° and showing no lights, or pairs of 50 cd, 150 cd, low beam and high beam lights. In the second experiment, subjective central conspicuity and response time were recorded for paired comparisons among six vehicles, 500 m distant, showing no lights, or pairs of low beam lights of 50 cd or 100 cd intensity and of white or amber colour. In the third experiment, peripheral detection distance was measured during the onset of twilight for vehicles approaching at a visual angle of 20^°, over a dry asphalt or snow-covered runway, and showing pairs of running lights of 0,100, 200 or 300 cd intensity. As expected, there was a strong interaction between illumination level, viewing angle and running light intensity. The normal vehicle low-beam falls within the range of intensity found acceptable for a daylight running light (300-1000 cd). Special running lights may, however, be superior, because they can be optimally designed from a functional point of view.