Citation

Lewin I. IMSA J. 2000; 38(1): 22-28.

Copyright

(Copyright © 2000, International Municipal Signal Association)

DOI

unavailable

PMID

unavailable

Abstract

Nighttime visibility is a critical issue to users of U.S. highways and to those involved in street lighting design. Roadway accidents occur at a much greater rate during evening hours than during the day. The main cause is believed to be reduced visibility due to low light levels. Recent research shows that the color output of the light sources used for roadway lighting has a significant effect on how well we see at night. This article discusses physiological features of the eye and vision; defines the lumen as the standard measure of light output; and discusses how the relationship of eye sensitivity to the lumen output from a given light source varies depending on the visibility conditions. Brightness, visibility, and color vision are also discussed within a larger context of research comparing metal halide and low-pressure sodium lighting under nighttime visibility conditions.