GravityLight, a five dollar alternate to a kerosene lamp, is ready for field testing after four years of development. Invented by Martin Riddiford and Jim Reeves, the lamp takes three minutes to stay illuminated for almost half an hour, drawing its energy from weight and gravity.

The pineapple shaped LED light is simply charged with a bag filled with sand or gravel weighing 25 pounds. The bag, which is hung from a cord in the system, is charged if it is raised to six feet. When released freely, the cord moves in slow motion just like a rope slipping on a pulley, providing light for thirty minutes. The intensity of light can be adjusted and more energy can be obtained for a shorter period.

Two terminals on the front can also be used as a generator to recharge other devices such as radio and batteries.

Talking to scidev.net, Reeves said that thousands of prototypes will be sent to mainly Africa and Asia for testing and mass production of GravityLight will start early next year.

The prototypes will be tested in all weather and harsh conditions in developing countries.

GravityLight will aim to replace other energy sources such as solar panels, kerosene lamps and solar lanterns, which are expensive and require more energy input. Kerosene lamps, which are used by nearly a billion people according to the International Energy Agency (IEA), have an adverse impact on health and income of poverty-stricken families, especially in Africa and Asia. An alternate such as the one provided by Reeves and Riddiford will be reliable, low-cost and eco-friendly.