Street lights waste energy in the wee hours of the night when no one is using them. It would be great to just turn them off, but then the occasional person coming home late from work or from a party would be left in darkness.
In a German town, they’re experimenting with a new system in which streetlights turn off after 9:00 PM. If residents need light, they dial a number and the lights are turned on instantly.
Great idea, and this would also make astronomers happy, as it minimizes light pollution!