The impact of road lighting on road user alertness in the evening

A laboratory experiment was conducted to investigate the alerting effect of light under lighting conditions typical of road lighting. After a 2-h adaptation period, under lighting representing a domestic interior, participants were exposed for a further hour to one of four lighting conditions, with illuminance at the eye and spectral power distribution varied to give a melanopic equivalent daylight illuminance of <0.5 lx to about 10 lx. During this latter phase, half of the participants remained seated, and the other half walked on a treadmill. The dependent variables were reaction time to an acoustic detection task, melatonin levels derived from saliva samples, self-reported sleepiness and skin temperature. The results did not suggest that differences between the four lighting conditions had a significant effect on any of the dependent variables, confirming the results of a previous study conducted on a test track. This suggests that any alerting effect of road lighting is not significant for driving or walking in the evening.