When do the traffic camera's flash?

Hey guys, so i have been having a debate with brother about traffic camera's and when they take pictures. I think that it flashes everytime th light turns red and he believes that it flashes when someone goes over the white line. Does anyone know which is right or wrong!? Thanks!When do the traffic camera's flash?
There is a sensor in the road that picks up cars passing over it. This sensor is positioned at the intersection boundary (nothing to do with the white line). The camera electronics are wired to the red light indication. When power is applied to the red light (by the traffic signal equipment) AND a car passes over the in-road sensor, the camera electronics takes your picture (usually 3 images in quick succession). There is usually a short delay before the picture is actually taken to remove any doubt about the red light violation.When do the traffic camera's flash?
I don't know for sure, but if they only flashed when the light turns red, then the camera wouldn't capture anyone going through the light after the moment it turns red. So I think it just flashes when someone goes past the line.When do the traffic camera's flash?
anything after red