Gravity-powered lighting

http://www.lostateminor.com/2013/04/05/gravity-powered-light/?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+LostAtEMinor+(Lost+At+E+Minor)
http://www.businessweek.com/articles/2013-03-14/innovator-martin-riddifords-gravity-powered-lamp
http://www.indiegogo.com/projects/gravitylight-lighting-for-developing-countries