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When gravity equals light

Posted on 03 July 2018.

Martin Riddiford and Jim Reeves invented a gravity lamp that works with no battery or fuel to replace kerosene lamps.

In 2009, Martin Riddiford and Jim Reeves decided to take up the challenge of developing a very low cost solar lamp for poor people with no access to electricity (1.2 billion people). Their goal is to create a healthy and sustainable alternative for the hundreds of millions of people in developing countries currently using kerosene lamps for light.

After realizing that batteries for photovoltaic panels were far too expensive, the two English engineers decided to turn to another source of energy. And an amazing source of energy – gravity! They invented the GravityLight, a lamp that works with no battery or fuel, simply a weight (see box).

In 2012, after several years in development, Martin Riddiford and Jim Reeves finally came up with a functioning prototype. They then set up a crowd funding campaign on the Indiegogo website. The aim is to finance not only the production of the first lamps but also their distribution to families living a long way off the power grid in Africa and Asia, and then collect feedback to improve the model and move into mass production.


Under 10 dollars

In 30 days, they collected just shy of US $400,000 (about €322,000), which meant they could test a thousand lamps in the field in 26 countries. The feedback was extremely positive and 90% of people who tried GravityLight said they would be willing to swap their kerosene lamps for the gravity lamp.

After a second crowd-funding campaign in 2015 and with several partnerships in place, they distributed the second generation GravityLight in Kenya, where it sells for under $10. The lamp is now also available in developed countries through Deciwatt – but at a much higher price.

The founders of The GravityLight Foundation wanted to go further by helping to boost the economy in the regions selling their lamp. In Kenya, the lamps are produced on the spot and local distributors are used - thereby creating jobs. It’s a virtuous model that could be replicated elsewhere on the African or Indian sub-continent.

Sandbag mechanics

GravityLight works by lifting a weight – in this case a simple weighted bag. As it descends it actuates a pulley system connected to an alternator that converts the mechanical energy (or kinetic energy) produced by the movement into electricity, thus powering the lamp. The device is very simple to use. The GravityLight is fixed 1.80 m from the ground and the bag filled with pebbles, sand or earth, until it weighs about 12 kg. The weighted bag is then lifted to the top using a cord. The system of pulleys makes the 12 kg feel like 3 kg! The bag descends slowly (about 1 mm per second), generating light for 20 minutes. Once it reaches the ground, just repeat the process.