design development technology

Light your home with gravity

A third of the world’s population lacks cheap electricity, and one of the most basic benefits they’re missing out on is electric light. It’s bright, steady, and safe. It’s also cheap. Buying kerosene for lamps is one of the biggest cash expenses in many unconnected African households. Since those lamps are also a fire risk, and they’re smoky and unhealthy, there are plenty of initiatives to try and replace them with something better.

Earlier this year I wrote about the ‘lightie‘, a tiny solar light that can turn a Coke bottle into a lamp. I’ve written about SolarAid and the WakaWaka light. These are all great, clean technologies with no ongoing fuel costs, but there are real challenges. The main problem is that solar panels aren’t cheap, and neither are batteries. To make a difference to ordinary Africans, it needs to be affordable – preferably under $10, in order to compete with the kerosene option.

gravity lightWhile working on this problem, engineers Martin Riddiford and Jim Reeves began to think that there may a cheaper and simpler approach than solar power. They started experimenting with gravity. Like a grandfather clock, a descending weight could produce the energy to power an LED.

To activate the light, the user lifts a 12.5 kg weight, such as a bag of sand. A cable then allows it to drop slowly, running through a series of gears to produce a little trickle of power. With modern efficient LEDs, this couple of deciwatts is still enough to run a light that is over twice as bright as a kerosene lamp for about half an hour.

The team refined the light over several phases, tested it, and crowdsourced the initial run of them last year. They’ve now been shipped to backers, and the light will go into production in 2015. They are expected to cost $6-7, and they expect future versions to be both cheaper and brighter and LED technology continues to improve.

The Gravity Light is a fine example of an appropriate technology, and I look forward to seeing them on sale next year.

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  1. Jeremy,

    Using gavity like this is not new. In the 70’s I taught science in Cameroon. We had a UK made Aerogen gas generator, that made gas for the labs from petrol and rainwater and was powered by a falling weight (and the unlucky pupil chosen to haul the weight up to the top).

    The technology you describe below should work well if the design is robust and easy to make & maintain locally. However, unscrupulous local traders could monopolise the supply of LEDs and keep the price high…but promoters of such technologies should be well aware of such risks.



    1. Nice example. I’ve heard of ceiling fans that are powered this way, but a gas generator is a new one to me. Thanks.

      Yes, the supply of LEDs is the obstacle to this being a ‘pure’ appropriate technology. Fortunately LEDs are very durable, so if anything’s going to break, it’s likely to be the gears, the casing or wear and tear to the hanging strap. The gears in particular would be harder to fix, so you’d want to include service and spare parts in the business model to make sure it’s a good option for low income households.

  2. Great idea, when might it be in the UK? Suppose that is subject to a distributor being appointed-as such no doubt the price will reflect at policy/distributor.

    1. Yes, I doubt they’ll be on sale for a fiver here. These sorts of projects tend to rightly prioritise the original mission of reaching developing countries, so it might take a while to get a distributor. We’ll have to wait and see.

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