This Ingenious $20 Lamp Gets All Its Energy From Gravity
GravityLight—a light that gets all its energy from its own weight—first appeared about three years ago. We wrote about it as it was launching on Indiegogo and went on to raise $399,590. It provides free light (after you've bought it). It's cheap. And it has none of the environmental or health side-effects as do other light alternatives in the developing world. But even all those things aren't necessarily enough if it's to reach its potential. If the company and foundation behind the device are to make it a success, they need a reliable product; they need to distribute it in places where distribution can be difficult; and, more fundamentally, they need to explain why someone should buy a GravityLight when there's plenty of good, cheap solar on the market today.