Evaluation of the necessary intensity of daytime running lights at different ambient illuminance levels

A previous analysis of traffic scenarios in central Germany indicated that significant energy savings could be achieved by extending the use of daytime running lights (DRLs) into dusk, instead of switching to low beam. This would lead to a reduction in CO2 emissions and potentially increase the range of electric vehicles. Studies at the TU Darmstadt have shown that such extended use of the daytime running lights at dusk is possible. The switching threshold between dipped beam (low beam) and daytime running light, which currently must be set at 1,000lx at the latest according to ECE regulations, could be shifted to lower illuminance ranges without reducing the visibility condition. Due to the lower ambient illuminance on the road, it can be assumed that even lower luminous intensities of daytime running lights are sufficient to achieve the goal of good visibility for other road users. Furthermore, it must be ensured that no disturbing glare occurs in this case. For this reason, a comprehensive field test subject study was carried out in this work, which analysed different dimming levels of modern daytime running lights regarding their visibility and glare. Not only the period in which the illuminance is below the current minimum switching threshold of 1,000lx was analysed, but also tests at illuminance levels far above 1,000lx. The results show that daytime running lights with a lower intensity than the 400cd required in the ECE regulations at the HV point are sufficient for horizontal illuminance levels between 1,000 lx and 10,000lx. Such a dimming of the DRLs offers further potential energy savings.