A method of manufacturing a device (100; 100'; 100") for use as reference material in calibrating an instrument to measure luminance of a road surface, the method being characterized by: providing a tabular dataset of reflectance values (r), in particular normalized reflectance values, of road surfaces illuminated by a road luminaire emitting light impinging thereon at an observed point, the light propagating from the road luminaire, in particular from a photometric center of the road luminaire, along a light path so as to determine, as seen from an observation point at a given viewing direction angle α with respect to the road, in particular of 1°: e) a first incidence angle (ε) between the light path and a normal to the road surface; and f) a second incidence angle (β) between a vertical plane passing for the observation point and the observed point and a vertical plane passing for the observed point and the road luminaire; selecting a subset of reflectance values from said provided tabular dataset of reflectance values (r); setting, as a function of the selected reflectance values, geometric parameters of a pattern (120; 120') of prismoid-like formations (122, 124, 126, 128; 122', 124', 126', 128') separated therebetween by channel-like formations (123, 125, 127; 123', 125', 127'), wherein said geometric parameters of the prismoid-like formations (122, 124, 126, 128; 122', 124', 126', 128') are selected so that respective areas projected at said viewing direction angle (α) have values proportional to the values of said subset of reflectance values selected from said provided tabular dataset of reflectance values (r); manufacturing, in particular by 3D printing, said pattern (120, 120') of prismoid-like formations (122, 124, 126, 128; 122', 124', 126', 128') separated by said channel like-formations (123, 125, 127; 123', 125', 127') onto a support base, in particular quadrangular, having a constant thickness (T 0), in particular as a single piece. providing a tabular dataset of reflectance values (r), in particular normalized reflectance values, of road surfaces illuminated by a road luminaire emitting light impinging thereon at an observed point, the light propagating from the road luminaire, in particular from a photometric center of the road luminaire, along a light path so as to determine, as seen from an observation point at a given viewing direction angle α with respect to the road, in particular of 1°: e) a first incidence angle (ε) between the light path and a normal to the road surface; and f) a second incidence angle (β) between a vertical plane passing for the observation point and the observed point and a vertical plane passing for the observed point and the road luminaire; e) a first incidence angle (ε) between the light path and a normal to the road surface; and f) a second incidence angle (β) between a vertical plane passing for the observation point and the observed point and a vertical plane passing for the observed point and the road luminaire; selecting a subset of reflectance values from said provided tabular dataset of reflectance values (r); setting, as a function of the selected reflectance values, geometric parameters of a pattern (120; 120') of prismoid-like formations (122, 124, 126, 128; 122', 124', 126', 128') separated therebetween by channel-like formations (123, 125, 127; 123', 125', 127'), wherein said geometric parameters of the prismoid-like formations (122, 124, 126, 128; 122', 124', 126', 128') are selected so that respective areas projected at said viewing direction angle (α) have values proportional to the values of said subset of reflectance values selected from said provided tabular dataset of reflectance values (r); manufacturing, in particular by 3D printing, said pattern (120, 120') of prismoid-like formations (122, 124, 126, 128; 122', 124', 126', 128') separated by said channel like-formations (123, 125, 127; 123', 125', 127') onto a support base, in particular quadrangular, having a constant thickness (T 0), in particular as a single piece.