The neighbor is producing more than they require; the only light the neighbor requires from their lamp is what falls on their page. The rest is (intentionally

The neighbor is producing more than they require; the only light the neighbor requires from their lamp is what falls on their page. The rest is (intentionally or not) scattered abroad to the environment, where it is as much theirs as the leaves on the plant in their window which are blown down the street. It's not stealing, because it's not taking, because it is possessed by no one.