A $5 Light For The Developing World With An Ingenious Fuel: Gravity

The GravityLight gets power from the slow lowering of a weight. All it takes is enough elbow grease to hoist the bag, and you can light a room with nothing but a bag of sand.


We’ve written about several projects delivering cheap electric light to developing countries. The need is enormous: more than 1 billion people still lack electricity, and many rely on kerosene–which is relatively expensive, highly polluting, and comes with multiple health and fire risks.


Many of the solutions out there are ingeniously solar powered. But GravityLight, an idea from two British designers, is something completely different. It gets its energy from gravity: A 22-pound bag of sand that gradually cranks a gear-train attached to a D.C. motor. One lift is enough for 30 minutes of light, and recharging is as simple as pushing the weight up again.

Martin Riddiford and Jim Reeves are crowdfunding the prototype on Indiegogo, and have already raised almost $100,000. They plan to distribute 1,000 units to villagers during a test stage, before developing and commercializing further. They estimate the current cost at $10 per machine, but reckon they can halve that by scaling up, and finding better materials.

The two initially worked with SolarAid, an NGO that wants to eliminate kerosene lamps in Africa by 2020, because the fuel is expensive and the fumes are bad for people’s health when trapped in a small space. But they soon found that solar has limitations. One, panels and batteries are still relatively costly, especially for durable models. Two, batteries deteriorate over time, and need to be replaced. And three, you have to dispose old units, presenting a potential environmental challenge.

By contrast, GravityLight works inexhaustibly as long as you have the strength to lift it, and provides light whenever you need it. You don’t need the sun to shine, or to store up enough power for evening’s use.

“There is a lot of money going into solar, and it’s being seen as the only way forward,” Riddiford says. “What we’re saying is there are lots of places that don’t have enough sunlight to charge panels. If you have two or three dull days, you are running out of light.”

The cheapest solar lamps, which include both panel and battery, cost only $5. But Riddiford says you don’t get much for that–he calls the models “toys”–and there are costs attached, such as the price of replacing batteries.


He’s not dismissing solar, though. “Once people have started saving money, after a year or so they might be able to afford a reasonable solar system, if they have enough sunlight,” he says.

Riddiford and Reeves don’t claim GravityLight produces a brilliant quality beam–it’s just better than what’s on offer at the moment. “Unfortunately the potential energy isn’t that huge. But it is sufficient light, and it’s free light, for someone who has no other access to electricity.”

The illumination is equivalent to a kerosene lamp, he says, but can be supplemented with “task lights” running off the terminals at the bottom of the unit.

“You can do a Christmas tree string of lights extremely well. The strange thing is that you can light 10 LEDs almost as well as one LED. So, you can have general illumination and have task lights,” Riddiford says.

It’s nothing like being on the grid. But, as Riddiford says, it’s already better than kerosene. During the testing phase, we’ll find out how it stacks up against solar as well.

About the author

Ben Schiller is a New York staff writer for Fast Company. Previously, he edited a European management magazine and was a reporter in San Francisco, Prague, and Brussels.