Instrumentation for mapping light intensity contours

Automobile headlamp illumination is of concern because uniformity and shape of the beam pattern are quite important for optimum road visibility and safety for oncoming drivers. The Society of Automotive Engineers´ specification on headlamp illumination [1] designates the maximum and minimum intensities at several spots within the beam. Many states require inspection of vehicle-mounted headlamps for illumination and aiming, and this test is commonly performed using a device which clamps on the headlamp lens. This clamp-on device is limited to checking the maximum intensity at beam center, rather than checking the overall beam pattern to the SAE-J579a specifications. In addition, mechanical limitations of this device have often resulted in the mis-aiming of vehicle headlamps. Present instrumentation available for measuring light intensity per SAE-J579a is primarily of the photo-cell type device, and the point-to-point measurement of light intensities is quite tedious and time consuming. A technique is described in this paper which incorporates electronic signal processing into a closed-circuit television system for displaying contours of constant illumination intensity. The technique is capable of rapidly performing vehicle-mounted headlamp testing per SAE-J579a and could be adapted for use at state inspection stations.