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Looking for a lamp that's fed by good old Newtonian physics, lasts about 4 hours and outputs a lot of light?
A VA Tech grad student is here to help. It's a gravity lamp!
Looking at the schematic for the Gravia shows that the falling weight is defined as fifty pounds, which is 22.7 kilos, which is indeed about as much as a variety of humans could reasonably be expected to be able to lift back to the top of the tube every few hours.
22.7 kilograms falling 1.22m in gravity of 9.8 metres per second squared gives you a grand total of 271.4 joules.
That, once again ignoring losses (which are likely to be considerable, seeing as there’s a ball-screw and an electrical generator in the Gravia), will by definition run a one-watt lamp for 271.4 seconds, or four and a half minutes.
If you downgrade the lamp to one tiny 0.1-watt LED night-light, you get three-quarters of an hour.