As long as you reset a weight every 30 minutes, you can have a continuous, battery-free light source.
Posted 12.12.2012 at 3:30 pmGravityLight: lighting for the developing countries from T4 on Vimeo.
Kerosene lamps used in off-grid, rural areas are a major problem. They're bad for people's health and the environment's. One startup's solution is to tap another, greener resource, something we all have in abundance: gravity.
The invention, GravityLight, does exactly what the name suggests: It keeps a light going through the power of gravity. As an attached weight falls, it pulls a cord through the center of the light, powering a dynamo. That dynamo converts the energy from the falling weight into power for the light. (It's the same idea as a hand-cranked device, just more vertical.) The weight can be set in a few seconds, and as it slowly reaches Earth, enough energy is generated to keep a light working for 30 minutes. As long as it's set every 30 minutes, it makes for a green, battery-free, continuous stream of light. Other, similar devices like battery chargers could be used through the same process, too.
The inventors say the gadgets can be sold now for less than $10, which would make a return on investment for owners three months after dumping kerosene lighting. And speaking of investments,... ( more at http://www.popsci.com/technology/article/2012-12/new-light-fully-powered-gravity )
