> Or perhaps the purpose of a lamp is not to light a room, but to darken a different part of the world (in comparison to the lit part)...

This brings to mind a recollection of an essay I heard back in high school which described lamps as "dark collectors." In it, "dark" was described as a physical substance that had to be "sucked" into a "dark collector" in order for a room to be lightened. Of course the Sun was purported to be a large, natural "dark collector." It was obviously pure drivel, but very entertaining nonetheless.