GravityLight[1] applied this concept at small scale: to power a white led in e.g. rural areas without power, a bag of dirt is suspended from a dynamo. [1] http

GravityLight[1] applied this concept at small scale: to power a white led in e.g. rural areas without power, a bag of dirt is suspended from a dynamo. [1] http://www.indiegogo.com/projects/gravitylight-lighting-for-developing-countries http://www.indiegogo.com/projects/gravitylight-lighting-for-...