To capture license plates at night requires that the screen be black until a car comes by. That's because the lights on a car are so bright that we have to set the exposure so that extremely bright source appears fairly dim. Otherwise the headlights will "bloom" into a bright mess and it will cause the lettering on the license plates to be washed out (over exposed) by the bright lights. If our settings are such that an extremely bright source like a headlight appears as a dim light source, the ambient light has no chance of producing a usable image. This is why it is critical that a dedicated license plate camera be used. You will never be able to use one camera to capture both license plates and general CCTV footage at night. During the day you can, but at night the camera needs to be set up to either capture license plates only, or general CCTV footage which isn't going to provide usable plate footage due to the washing out effect of headlights.