What are the Little black box's on top of traffic lights are they sensors or cam

[ashiq22]

The sit on top of lights facing front of car and are about the size of childs shoe box and have black perspex on the front my mate and i have been trying having this discussion for years i think they are just sensors he thinks they are red light cameras and i also think if the roads quiet and you flash your lights at them they change quicker can anybody tell me what they are and who is right.


Thanks


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