Just a bottle filled with water (and a bit of bleach): it's amazing how much light it appears to give off. Obviously only works during the day but for homes without electricity it can be surprisingly dark inside even in the middle of the day. I wonder how well it holds up to rainstorms though (Personally I'd aim for the peak of the roof where you could flash the sheeting to shed water away from the hole).

http://isanglitrongliwanag.org/
video here