Citation

Marsh CR. Highw. Res. Board bull. 1958; 191: 41-48.

Copyright

(Copyright © 1958, National Research Council (U.S.A.), Highway Research Board)

DOI

unavailable

PMID

unavailable

Abstract

In daytime fogs, most vehicle parking lights are less visible than the car itself. The lower beam of the headlamp is inadequate, but the upper beam provides better forward visibility and should be used. A polarized spot lamp and cross polarized viewer is the most effective fog light system developed, although polarized lights penetrate fog to no greater extent than unpolarized light. A higher brightness lamp for use in daytime and in both day and night fog is needed to contrast with the high brightness of daytime fog, or, at night, with the fog illuminated by scattered light from vehicles and street lamps. The following list of attributes of the lighting system suitable for satisfactory performance in fog is advocated: (1) the volume of illuminated fog between the driver and the road should be small, (2) the light which must traverse this volume of fog should do it at angles with the driver's vision which produce the minimum light scattering, (3) direct glare sources should be minimized for fog as well as clearer atmospheres, and (4) except for haze having particles much smaller than fog droplets, color seems not to be a factor in scattering.