In night-time traffic in zones that are not illuminated, the only light sources allowing obstacles and road signalling to be seen are the headlights of vehicles. Since most signalling devices are not themselves luminous, their luminance depends on the quantity of light that reaches them. The spatial and energy distribution of the luminous flux of the beams from vehicle headlights is therefore an important parameter both for the detection and legibility of road signalling devices (horizontal and vertical) and for the perception of various obstacles. A measurement device based on the principle of the headlight tester associated with a CCD camera and image processing software was developed to perform the photometric survey of the luminous beam from the vehicle headlights. This device was used to investigate the influence of a number of parameters, such as the type of lamp, the adjustment of the headlights, and dirtiness, on: the spatial and energy distribution of the luminous flux; the predicted legibility and detection distances of vertical signalling; and the detection distances of horizontal markings. (A)
Abstract