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gravity powered lamp (updated)

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There is a lamp powered by gravity. The energy is created by a weight slowly sliding down some rail and you recharge the lamp by moving the weight up again. The motion is then converted to electricity and used to power the LEDs which create the light. I want one of these lamps!!!

Update. A quick calculation shows that this lamp cannot possibly work: the best possible efficiency for generating light is approximately 683 lumen per watt (real efficiencies are much lower), thus to get the advertised 600-800 lumens … over a period of 4 hours one would need more than 12650 joule. Since lifting a weight of 1 kg by 1 meter only provides 9.81 joule, the lamp, even assuming 100% efficiency, will never be able to generate enough electricity to power the LEDs.

This is an excerpt from Jochen's blog.
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