CIE x050-PP020 PDF

For road lighting design, road surface descriptors like the degree of lightness Q₀ and specularity S1 are derived from reflection properties (or BRDF) of road surfaces. However, these BRDF are based on outdated road surface characteristics, and are also partial (they are called r-tables) because only the motorist’s 1° observation angle is considered. Thus, the need to have full BRDF measurements of current road surfaces available. This paper proposes to use a recently released open source database of measured whole BRDF by means of our in-lab gonioreflectometer to investigate the performance of Q₀ and S1. We first compare descriptors obtained from measured and interpolated r-tables and find a good accuracy, especially for Q₀. Then we propose a tentative model for these descriptors function of observation angle, and find quite an accurate fitting. Finally, we suggest a methodology for the classification of road surface materials in terms of Q₀ and S1.