A team of UK engineers has developed a light that can work without batteries, electricity or sunlight – all it needs is the force of gravity.
The new device called GravityLight works a bit like a pulley.
All you need to do is add 12kg of weight to one end of the bead cord (this can be a bag of sand, rocks, whatever you like), and then lift that weight up by pulling down on the lamp attached to the other end.
Thanks to gravity, the weight slowly descends back down to the floor, transforming potential energy into kinetic energy as it drops.
This kinetic energy then powers a drive sprocket and polymer gear train that lights up the LED as it goes.
Once the weight gets to the floor, the light goes out and you need to repeat the process, but each pull provides you around 20 to 30 minutes of light, depending on how high you lift the weight up in the first place.
This is certainly good news for the estimated one billion people in the world who still live without electricity.
The team is now hoping to raise seed funding to take the project to the next level, making the light brighter, longer-lasting and easier to use.
The light itself will only cost around US$10 – much cheaper than a kerosene lamp.
GravityLight will be initially targeted to families in developing countries, with an initial focus on Kenya.
The team hopes to provide local jobs by creating and selling the lights there.
Of course, the best thing about gravity is that it's free, so once the initial investment has been made, the lights literally cost nothing to run.