Spectral characteristics of road surfaces and eye transmittance: Effects on energy efficiency of road lighting at mesopic levels

In 2010, the CIE published a recommended system for mesopic photometry based on visual performance. According to this system, scenes illuminated at mesopic levels with light sources of high S/P ratio, will produce better visual performance than those illuminated with light sources of a lower S/P ratio at equal photopic luminance. However, there could be other factors affected by SPD that, when quantified, could lead to a contradictory final effect. The scope of this paper was to evaluate how road lighting is affected by the spectral road surface reflectance and by the human eye transmittance as people get older. Our results suggest that the benefits of considering the mesopic vision effect for light sources with high S/P ratios are totally counteracted by the other two effects at mesopic luminances between 0.75cd/m(2) and 1.73cd/m(2) for people between 20 and 60 years of age, depending on the light source and the age of observers.