New cost-effective sensor for the characterization of automotive headlamps by measurements in the near field

Nowadays, European Normative regarding headlamp validation evaluates the photometric distribution of the source as a series of illumination values measured at a plane placed 25 m away from the light source. An innovative and inexpensive approach to test this photometric distribution is presented. We propose to sample the luminance field at a plane placed a few centimetres in front of the headlamp displacing a CCD camera at an adjustable number of positions. A specific processing of the sequence images allows simultaneously measuring the direction of propagation through deflectometric techniques and the energy of the light beams leaving the source through photometric techniques. Image-processing techniques may then be applied to these data in order to evaluate the photometric distribution in any predefined distant surface. An overview of the unit, of the measurement principle, and of the main calibrations performed is presented along the paper. In particular, the techniques for the calibration of the global constant converting CCD grey level values into photometric units are described and applied to different distributions. Finally, the comparison of computed illumination maps using the unit with reference measurements at photometric tunnels is presented, showing good agreement and demonstrating the validity of the approach. (c) 2006 Elsevier B.V. All rights reserved.