A CCD camera system is placed on our test road to measure the headlamps beam luminance. Such task could give a very quick indication of the beam quality. By the luminance distributions and their sections in any direction, the headlamps behaviour can be evaluated and possible homogeneity defects discovered. In such case, a comparison with the related 25 meters screen measurement or simulation sections could supply some information useful for new optical designs. Many practical cases will be analysed and the related results will be presented in this paper. Generally, in the designing phase all simulations are plotted like isocurves on the screen; in fact the measurements are performed on the screen as imposed from legal requirements. However, the final customer will see the result on the road. To have an idea of the road distributions, the screen simulations or measurements are projected on the road. The curves obtained in such a way generally represent the illuminance of a possible obstacle nearly perpendicular to the optical axis. The visual comfort imposes a good luminance homogeneity in order to avoid points by which the drivers eye could be attracted. In theory the ideal homogeneous beam will produce a bi-dimensional plot with a constant luminance in each point and a large distribution in order not to see the borders. In fact, a good result could be obtained with the luminance decreasing from the road center zone toward the road borders in a regular way, with a profile without secondary maximums or minimums for each spatial direction. From the visibility point of view, it would be necessary to increase the road luminance values in order to make the threshold contrast lower. Also a good visibility is linked to a regular luminance profile, because an object is more detectable if emerging from a uniform background.
Headlamp road measurements by CCD camera and related guidelines for lighting design
Scheinwerfer-Teststreckenmessungen mit einer CCD-Kamera und Richtlinien für die Dimensionierung der Beleuchtung
2003
13 Seiten, 14 Bilder, 3 Quellen
Conference paper
English
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