Seeing as I'm a gamer, I tend to mess around with some of the programs that ship out with games, such as UnrealEd, and the TES Construction Set that comes with Morrowind (Oblivion's you have to download).

In the TES construction sets, the light placeables have a little checkbox you can put a tick in to make a light source "negative." When that is checked, it ignores the light's color (if any), and uses the radius and intensity applied to it to diminish the strength of light being emitted from other lights. In a nutshell, it "sucks" light out of an area where you don't want light (or less of it).

My question is...does Maya have anything similar to this; a light "source" that you can have suck light out of a certain area?