Your presumption is probably incorrect for a large number of lights. From what I've seen most streetlights around me in residential areas run off both mains with the neutral disconnected, implying they're running off the full 240V. Bigger lights probably run off even higher voltage runs.

Its a common misconception the US infrastructure is a 120V system. Your home has 240V and likely even has 240V appliances connected. Your individual outlets are only connected to one half of that 240V service.