Much talk hither and yon about a year ago re a "gravity powered light" and it's likely capabilities and chances of getting to market. They reportedly have got to a alpha or beta release candidate version (not what they call it). http://www.theregister.co.uk/2013/12/05/gravitylight_rolls_into_production/ Home page: http://deciwatt.org/ As the name implies, output is nominally 100mW. The Register article says: Well, the initial GravityLight was just a prototype - it wouldn't hoist more than 10kg, and it wasn't really safe to use. It broke easily. The team has also made it more compliant with safety regulations - and it now gives unmissable visual feedback if it's overloaded or tugged, by flashing red. Bearings were stripped out, and it's now a robust piece of kit, capable of holding 7.5kg to 12.5kg of weight. And it now contains gears - so you can run an LED for 30 minutes at lower power, or 15 minutes of higher power, with an intermediate setting giving 22 minutes of light. Kits are going out to Guatemala, the Philippines and Bangladesh to gauge real user feedback. The proposition, Riddiford explained, is: do you want to save a few cents a day in fuel by lifting a weight? If people find that acceptable, then it's likely to go to the next stage. The economics, Riddiford told us, are compelling. Each hoist saves about 1 cent's worth of kerosene. Over two years this adds up to a saving of $100 - so the device pays for itself quite rapidly. Their $100 saved in 2 years figure infers 15 reloads/day and a break even time of under 3 months at a market cost of $10. A figure of 100 mW output at full power is mentioned. Elsewhere they say 2m (about) lift, 12.5 kg max load, and 15 minutes at high power. The mass x head gives 250 Watt second of input energy. 15 minutes at 100 mW is 90 Ws of LED power for an efficiency of potential energy to LED input of about 35%. If they in fact achieve that overall it's a very creditable result. 100 mW at 150 lumen/Watt (which hopefully they will equal or exceed) =3D 15 lumen =3D useful. One person can read a newspaper page (say A2) at a comfortable level with 15 lumens. (Evenly distributed that would give 60 lux which is low by Western standards but enough for comfortable colour rendition). Real distribution will not be wholly even, but 15 lumen is still very useful. One of these could power a light in an otherwise unpowered washroom or toilet cubicle, with a single pull giving 15 minutes of lighting. (A useful addition to any remaining "pull the chain" toilets of yesteryear. Make a ratchet device powered by walking on a step and small increments could be added as each person passes a point. A 10mm fall in a step would probably be unnoticed and a larger fall if known of would be acceptable when walking down stairs. 10mm gives about 5 seconds of full output and 100mm gives 50 seconds. A children's swing game that uses descent energy could provide many recharges per minute. (An idea I included in a proposal for a developing country charging system proposal some years before DeciWatt surfaced - it was not accepted). At say 25% overall, energy ~=3D meters_fall x kg x 10 m/s/s x 25% W.s (=3D Joule) =3D 2.5 x m x kg [The idea is far from new - some early 20th century homes were lit by gravity powered electric lighting with weights in the ton range and servants using suitably geared winches to raise the weight. ] Russell --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .