The problem of bringing light to remote parts of the developing world has been tackled in the past with everything from solar-powered lamps to wind-up devices and rechargeable batteries – all of which require relatively expensive kit or physical effort by the user.

But two London-based designers have now developed a light source that operates on the stuff that surrounds you – earth, rocks or sand – with the helping hand of gravity.

Developed by Martin Riddiford and Jim Reeves over the last four years, the GravityLight is simply charged by a bag that is filled with around 9kg of material and hung from a cord below the light. As the bag descends, a series of gears inside the device translates this weight into energy, providing 30 minutes of light. The light strength can be adjusted, from strong task lighting to a longer-lasting low-level glow, and two terminals on the front allow it to be used as a generator so it can recharge other devices including radios and batteries.