Vid An ingenious gravity-powered light source has reached its first funding goal in four days. Co-invented by industrial designer Martin Riddiford - who crafted Psion's hardware - the cheap kit allows an LED to be run for 30 minutes from a three-second pull on a rope. Gravity does the rest.

The GravityLight was devised with developing countries in mind - areas without sophisticated power grids, and where low wages leave batteries and solar panels prohibitively expensive. The kit includes an LED lamp and a sack that is filled with sand, rocks or whatever is to hand. The bag is attached to a rope threaded through a mechanism that generates the electricity: after pulling the sack up, it slowly descends, feeding the cord through the machine and powering the electric dynamo.

This video demonstrates how it works:

Once produced in volume, the unit could cost as little as $5 per unit at wholesale.

The first round of public fundraising exceeded a $55,000 target, which is intended to pay for tooling and produce the first units.

Both Riddiford and co-inventor Jim Reeves are directors at London-based Therefore, whose clever industrial designs range from the hand-pulled Rok espresso machine to the TomTom satnav. The company was founded with an equity investment from Psion founder Sir David Potter, and it designed all the celebrated British computer company's casings, from the MC series laptops through to the Wavefinder DAB radio.

"We've done a number of projects, including the Psion products - where the requirements were incredibly efficient in terms of power usage," Riddiford told The Reg. "The digital age has made products much power hungry but now there’s a reversal of that – everyone’s chasing lower power again."

The GravityLight is no substitute for the modern power grids developing countries need - but it in the interim it could save people relying on biomass fuels and kerosene, which are bad for one's health.

The team is investigating using the GravityLight for powering other devices such as water purifiers or even mobiles, and how they can work in serial or parallel.

You can find out more at the project's deciwatt website or show some love at the funding site, which is here. ®