Measuring Reduced Luminance Coefficients for Asphalt Based on Imaging Method

Reduced Luminance Coefficients for asphalt describe how light is reflected, based on the bidirectional reflectance distribution function (BRDF). This function is measured with the help of goniometers and samples in the laboratory. There are also various methods of in situ measurement, some global or others also based on the goniometer. Compared to these methods, an imaging measurement can provide all the information needed to obtain these values. The paper describes the working method, in which a light scene is created, in a configuration very close to the geometry by which Reduced Luminance Coefficients were defined, in EN 13201. An isocandela light source is used, and from the measurement of an illuminated surface of the asphalt can spatially locate the measuring points, in polar coordinates, according to r (γ, ß) Table. It presents the details of the geometry that is involved, as well as an interpretation of how these coefficients are used in the design, in their measurement. The way in which the observer is considered to target the street scene, from a unique angle (as in EN 13201), is difficult to accept in reality. From this point of view, the imaging measurements are more realistic, because the viewing angle is higher for the close points, as it is in reality.