Compact System for Photometric Characterization of Automotive Headlamps

We present a system allowing the determination of the distribution of light at any given distance (e.g. 25m) from a light source, by measuring the intensity and direction of the illumination distribution at a closer distance (e.g. near 20 cm). The measurement principle is based on the acquisition of images taken by a CCD matrix-sensor through an optical system focused at infinity. A sequence of images is obtained by moving the camera at different positions in front of the source. The process involves the accumulation of shifted images and corrections for optics (geometrical distortion and vignetting) and electronic shutter (exposure time). We describe the developed experimental set-up and the calibration procedures needed to obtain absolute photometric values. We present results obtained for automotive headlamps: computed relative illumination distribution is very similar to that obtained using a reference given by a measurement tool using a lightmeter. Absolute calibration of the system is performed from the set of measured points