We had the first big thunderstorm of the summer through Wigton at breakfast time a couple of weeks ago. The streetlights came on. They must be fitted with light sensors. These can't be simple Light Dependent Resistors because these use energy from photons to promote electrons from the valence band to the conduction band. More electrons in the conduction band means higher current so we say that the resistance is lower. (I think this is a bit of a cheat because it doesn't mean that the lattice ions are vibrating any less). So in the dark the resistance will be higher. Less current would not put the light on. So it must make use of electronics. A NOT gate would flip the input.
