An apparatus for measuring the retroreflectivity of a surface. The apparatus comprises a light source for illuminating an area of said surface at an incident angle relative to the surface; a detector for detecting light reflected back from the surface at an observation angle relative to the surface; a signal processing unit adapted to receive a detector signal from the detector and to determine, from at least the received detector signal, a measure of retro reflectivity of the surface; a range finder for measuring a distance between the apparatus and the illuminated area. The signal processing unit is further adapted to adjust the measure of retroreflectivity responsive to the measured distance.