Now, a bulb powered by gravity for India

The 'GravityLight' uses a sack of sand to gradually pull a piece of rope through a dynamo mechanism which generates electricity to power an Light Emitting Diode (LED) light.

Manufacturers claim a three-second pull on the rope to raise the sack will keep the LED bulb running for up to 30 minutes, the 'Daily Mail' reported.

The London-based design and innovation initiative deciwatt.Org, designed the GravityLight as a sustainable solution for 1.5 billion people who rely on biomass fuels like kerosene for lighting, which can be hazardous to health.

Deciwatt.Org, a division within design company Therefore, said the trend for rapid advances in technology has made their product possible.

The relatively simple devices progressively need less energy to run, making possible a whole range of relatively simple gadgets that can be powered by unconventional means.

The GravityLight was co-invented by Martin Riddiford and Jim Reeves, both directors at Therefore.

"We've done a number of projects, including the Psion products - where the requirements were incredibly efficient in terms of power usage," the paper quoted Riddiford as telling The Register.

"The digital age has made products much power hungry but now there