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.