The effect of dimmed road lighting and car headlights on visibility in varying road surface conditions

This article evaluates the potential of dimming road lighting in order to save energy and lower costs while avoiding any adverse effects on the visibility of drivers. An experimental study under varying road surface conditions was conducted to examine the combined effect of car headlights and different road lighting intensities on the visibility level. The luminance levels of the road surface, contrast and visibility level of the objects were measured from a stationary car under three road surface conditions: a) dry, b) wet, and c) snowy conditions. The results support the feasibility of reducing road lighting intensity when car headlights are available. When within the range of car headlights, road lighting did not improve the visibility level. In the presence of car headlights, the average luminance providing a sufficient visibility level was found to be 0.19, 0.63 and 0.75 cd/m2 under dry, wet and snow conditions, respectively. This would allow an energy savings of 317kWh/year/luminaire, representing savings of 80% luminaire/year for LED luminaires.