The GravityLight gets power from the slow lowering of a weight. All it takes is enough elbow grease to hoist the bag, and you can light a room with nothing but a bag of sand.
Many of the solutions out there are ingeniously solar powered. But GravityLight, an idea from two British designers, is something completely different. It gets its energy from gravity: A 22-pound bag of sand that gradually cranks a gear-train attached to a D.C. motor. One lift is enough for 30 minutes of light, and recharging is as simple as pushing the weight up again.
Also read: http://www.indiegogo.com/projects/282006