Visual aspects of daytime running lights

Literature data were collected regarding the visual aspects of Daytime Running Lights, in order to aid the development on international regulations. Topics treated are intensity of the main beam, lamp size and colour, and angular distribution of intensity. One important result of this study is a graph relating the intensity of the main beam to the percentage of daytime (average per year, at moderate latitudes) for which the lamp contributes appreciably to the conspicuity (in terms of detection distance) of a car. It is concluded that there is a considerable stress between conspicuity enhancement and glare limitation. Lamp size (in the range 50 - 200 square cm) and colour (amber, yellow or white) are not very critical. A horizontal beam width for half-peak intensity should preferably be not less than 45 degrees to the left and to the right, in order to improve conspicuity in a variety of collision courses.