Lighting for Intelligent Transport Systems: Practical Tips
Advanced information and communication technologies used in transportation and traffic management systems capture license plates, for which the distance to the target, the horizontal field of view and the camera mounting position must be carefully considered. White light, infra-red or another frequency light may be required for some plates from around the world. The spread of the high power, high quality illumination should be matched with the field of view of the camera and lens. Mount the lighting as close to the camera as possible and make sure to mount the camera/light combination at an incidence angle of less than 35 degrees to capture retro-reflective plates. Infra-red lighting is generally used for ANPR applications, particularly if no color information is required from the capture of the plate. Some systems will require white light to obtain additional information from the plate but then care must be taken to avoid blinding the occupants of the vehicle, particularly the driver. In infra-red systems, fit the lens with an 850nm narrow band-pass filter.