Not everyone has access to electricity all the time. And not everyone has access to chemical energy or solar energy or nuclear energy all the time. But everyone on Earth has access to gravitational energy whenever they need it. The problem has always been making gravity useful for something, but this gravity-powered light manages to do exactly that.
Essentially, this light (called GravityLight) operates just like a grandfather clock: there's a weight attached to a cable, and as the weight descends, it pulls the cable through a mechanism to extract energy from gravity-induced motion. You recharge the clock by winding it, putting energy into the system by using mechanical effort to lift the weight up against gravity. And there's a reason why people still have grandfather clocks: it's a very simple, very dependable system that's super easy to recharge.
GravityLight is designed to replace kerosene lanterns throughout the developing world. There are lots of reasons why doing this is a good idea: kerosene is bad for humans (having kerosene lamps burning in a house is equivalent to smoking two packs of cigarettes a day), bad for the environment (it produces 244 million tons of CO2 yearly), and bad for finances, sucking up between 10% and 20% of a developing household's income. The key to making something to replace kerosene is simplicity, dependability, and cheapitude. GravityLight has all three of these things going for it.
- It's simple: it's a box with a light on it that comes with a cable and a bag. Run the cable through the box, fill the bag with dirt or rocks, hoist it up, and you've got 30 minutes of light. When the light shuts off, just lift the bag up again.
- It's dependable: GravityLight doesn't have any fancy batteries or electronics inside it. It produces power on-demand only, so it should last a long time, even under heavy use. It also comes with a pair of terminals that can use GravityLight's power system to charge other electronics, like cellphones.
- It's cheap: the first iteration of GravityLight will cost under $10 (eventually under $5), and produces light with zero operating costs. It will pay for itself in just a few months with the savings from not having to buy kerosene.
You, of course, being not in the developing world, will have to pay a bit of a premium to make sure that the GravityLight stays cheap for everyone else who needs one for more than novelty. The project is on Indiegogo right now (where it's already nearly funded after just a few days), and $60 will get you a GravityLight of your own while donating a second GravityLight to a villager in the developing world. Doesn't get much better than that.
Check out the video below for more details on the GravityLight project.