And still, there are ideas that is so incredibly simple and yet, so incredibly useful, that I often kick myself of not thinking of them first.
One such ideas is the "GravityLight".
Basically the contraption is an LED device attached to a heavy bag.
Lift the heavy bag up and the "spring" or whatever inside winds up storing up the potential energy and when the bag is released, gravity takes over.
As the bag slowly descends, the LED light will shine for about 30 minutes.
Another lift, another 30 minutes of light.
Simply can't argue with the marvelous ingenuity.