This paper presents the research of optimization of road lighting energy consumption by utilizing the fact of human twilight and night vision (mesopic vision) dependency on luminance level and lamp’s light spectral composition. The research was conducted for a suburban street illuminated by smart LED road luminaires with a luminous flux control system with which different luminance levels can be achieved on the road. This road is an access road leading to a town located on the outskirts of Warsaw which is the capital of Poland and a large metropolitan area. Therefore, the traffic here is quite heavy on this road in the morning and in the evening and it is very light at other times of the day. In accordance with EN 13201 standard, lighting control can be applied to illuminate this road. This paper compares energy consumption for different lighting scenarios of the road in question. In the first scenario, the road luminance is compliant with M4, M5, and M6 lighting class requirements depending on the time of the day. In the second scenario, for each M lighting class, the values of luminance levels provided by EN 13201 standard have been reduced to the values resulting from their conversion to the corresponding mesopic luminance values. The conducted research has shown that a 15% saving per year in electricity consumption on the road is possible with such a conversion. Therefore, energy efficiency of a lighting installation can be improved by matching the lighting levels provided by the standard to the mesopic vision.

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Measurement of reflectance properties of asphalt is an insufficiently addressed problem, although this parameter is involved in three major directions in which the development of roads and lighting takes place: new technologies for materials, including solar energy harvesting, energy efficiency of road lighting and light pollution reduction. For each of these directions, concerns for improving performance have been identified, in which for each percentage gained, significant efforts and costs are registered. It is thus shown that although the reflectance properties of asphalt can change the results to a large extent (even 47%), this parameter is considered as a material constant and is not measured, although it is variable over time. After evaluating some landmarks regarding the geometric domain for which this parameter must be measured, a photographic method is presented and exemplified by which the desired values can be obtained insitu conditions.