GravityLight: The device that generates light from gravity

You’ve heard of solar-power, wind-power, and even poo-power, but the latest renewable energy innovation uses gravity to generate electricity.

The GravityLight device was invented by Jim Reeves and Martin Riddiford as a much-needed solution to an important problem. 20% of the world’s population has no access to electricity and so many rely on kerosene lamps, which are expensive, a fire-hazard and give off harmful fumes, to light their homes.

When they set about finding a safer, low-cost alternative to these lamps, Jim and Martin originally looked into creating a solar-powered product, but soon encountered a problem.

“It was quite clear that a big chunk of the fundamental cost was driven by the need to store power in rechargeable batteries”, said Jim, “and in small eco-solar products the rechargeable batteries can make up to a third of the cost of the product.” The conclusion was to avoid the need for batteries by building a product that could generate power as and when it was needed, and gravity won out as the cheapest and simplest solution.


GravityLight generates light from gravity

How it works

  • The GravityLight is designed to be hung from the wall or ceiling and features a hook for hanging a weight from.
  • The weight comes from the supplied bag that can be filled with rocks, sand, or any other available materials that are suitably heavy.
  • By pulling a cord, the weight is lifted by up to 1.8 meters (6 feet). Then, once the cord is released, it begins to fall slowly
  • The downward movement of the weight pulls on the cord, which powers a drive sproket, causing it to rotate slowly with high torque (force).
  • A polymer geartrain running through the device turns this input into a high speed, low torque output that drives a DC generator at thousands of rotations per minute.
  • This generates electricity, which is used to power an onboard LED light.
  • The weight takes approximately 20 minutes to fall the full 1.8 meters (6 feet), and when it reaches the bottom, the light goes out.
  • The bag can then be lifted to start the process all over again.

Thanks to a successful crowd-funding campaign, the first version of GravityLight has already been trialed by several families, helping to highlight a few key problems.

“One challenge that came out through the field trails was the need to withstand the sudden addition of an 8-year-old child swinging on the bag” said Jim, “so we have developed a couple of mechanisms that take care of this. When you reach the ideal target weight or slightly exceed it, there is a mechanical trigger in the device, which gives you a red LED alert and cuts out the white light output. The bag then descends swiftly but safely to the ground without stripping the gears.”

As well as fixing these issues, feedback from the trail has also enabled the team to improve the device in a number of ways. “We found through the consumer trial that the weight was challenging for women and children to get to the full lift height,” said Jim, “so we have reconceived the way that you charge the device, enabling you to input 2 or 3 kilos of force in pull to winch a 12 kilogram weight up off of the ground.”


Included with the GravityLight unit is the drive belt, two hooks, two bags for the weight and two large zip ties.

The new and improved GravityLight, GLO2, now has its very own crowd-funding campaign with a goal of setting up an assembly line to manufacture the device in Kenya. However, the uses of the device are not limited to kerosene lamp replacement, as the team also envisages it being used for emergency lighting.

Jim explained: “Products that contain rechargeable cells have a shelf life, so if you want to be able to put them away as a provision for a humanitarian disaster, then you risk them being spoiled by the time they need to be deployed. However, GravityLight has nothing to perish if the product is stored in the correct way, so it will be instantly available at some indefinite point of time in the future.”

That’s not all though, as Jim also highlighted another handy application for the device; “I have one at home attached to the end of my kids’ bunk beds. It makes a fantastic reading light because it puts itself out after a certain period time.”

If the new crowd-funding campaign is successful, GravityLight is expected to start shipping in Spring 2016, and if you make a generous donation then you will be added to the waiting list. However, this doesn’t mean that Jim and the team have stopped developing their creation.

“We’re in the process of producing an FM radio accessory that you plug into the device,” said Jim. “The radio is pretty ubiquitous for entertainment and education purposes in off-grid territories and at present a lot of people use their mobile phones as a method of accessing it, which adds another pay-as-you-go expense to the household. So providing free and on-going FM radio would be useful. An accessory for recharging AA and AAA batteries is also in the pipeline and we are looking at a number of other potential applications that we can add to the GravityLight’s functionality to help those living off-grid or preparing for a disaster.”

GravityLight is the winner of Ben & Jerry’s annual sustainable business competition Join Our Core. If you’d like to find out more or back GravityLight please visit

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