Portable instrument to measure the average luminance coefficient of a road surface

We describe a portable instrument that measures the average luminance coefficient of a road surface, Q0, in the field. The design employs a modified integrating hemisphere with light-emitting diode lamps as light sources and a calibrated charge-coupled device luminance meter with an observation angle of 1° as the detector. The diameter and weight of the hemisphere are 50 cm and approximately 8 kg, respectively. After first demonstrating proof of concept of the instrument, we calibrated the prototype with two methods and evaluated the performance by comparing its measurement results with those obtained by a gonioreflectometer for a series of samples. The performance characteristics of the instrument are appropriate for in situ Q0 measurement. (paper)