So that'* a blocked off ROOM under the stairs? Because if there'* no light in there and the flash on your camera is the only thing providing light (assuming that light bulb is off, which it would be because the safe would fall through the electrical), it would probably be a dark hole. Some light would get in from above, but not much (well, your flash would). If this is the case a PS wouldn't be as tough. It would be more possible to make it believable anyway, as long as the hole was convincing enough. But your flash would be an issue because it would still shine through the hole.