The Effect of Dimmed Road Lighting and Car Headlights on Visibility in Varying Road Surface Conditions

ABSTRACT 

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 snowy conditions, respectively. This would allow an energy savings of 317 kWh/year/luminaire, representing savings of 80% luminaire/year for light emitting diode (LED) luminaires.

KEYWORDS :

• Car headlights
• cost saving
• dimming
• energy saving
• road lighting
• road surface conditions
• visibility level

Acknowledgments

The authors' special thanks go to our colleague Åsa Enberg, who helped us with traffic safety arrangements. The authors also acknowledge the city of Helsinki for providing us with the opportunity to dim the lights in a section of the Munkkinieminranta road.

Disclosure statement

The authors have no conflicts of interest to declare.

Additional information

Funding

This research was supported by the Aalto Energy Efficiency Research Programme (the “Light Energy—Efficient and Safe Traffic Environments” project).