Harnessing the power of our very available yet insufficiently-used source of energy, GravityLight 2 improves on its original design, getting brighter—and a little more robust.
The light is charged by hoisting a weight of your choice to the base of the device. As the object descends, it'll drive a DC generator and power under a tenth a watt of LED power. Once the weight reaches the floor, you get around 20 minutes of continuous lighting.
In addition to increased brightness, this second iteration of the GravityLight features the added ability to maintain luminosity while charging.
Grab one here for $70.