Personally, I would have installed an X-10 or other remote switching mechanism on his light and shut it off every night when they went to sleep. Let them figure that out for a while.

A parabolic mirror, just on the edge of my own property to refocus a beam back into one of their windows would also be fun.

If I was blessed with one skill in life it's that I tend to not lose at such games.

With great power comes Awesome irresponsibility.