In a strange quirk of fate, on the very same day that Collin was regaling you with stories of the batteryless calculator, I was given, as a belated birthday present, a torch that worked on the same Faraday principle. The blurb says "Never needs batteries, never needs bulbs, waterproof, visible for over a mile." Using a super bright blue LED light, if you can shake the "Forever Flashlight back and forth for 15-30 seconds, enough electricity is generated to light the LED bulb for up to five minutes of continuous light." The box for mine actually reckons 1 minute of shaking will give 30 minutes of light, but it seems to use two coils, so maybe this helps pump in a bigger burst to the rechargeable capacitor? (And Excalibur do suggest the market is awash with imitations.) Apparently the strong magnetic coils can upset pacemakers, credit cards and cathode ray tube monitors, so is best kept a distance from such items. The Excalibur models range from about $20 to $40 USD and they've added a new dynamo version for about $25 USD. (1 min of winding for 45 mins of light.) ::Forever Flashlights.