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A Challenge: DIY gravity lamp Answered

I have decided to power the lighting in my house with gravity alone starting next year. The idea started here: Greener Gadgets: Gravity Lamp

I have some ideas about how to make it possible using some existing instructables and I though I would share this to get people thinking about new ways to use gravity as a power source. Think about it, gravity is clean, constant, eternal and EVERYWHERE.

I think that this instructable has some of the essential components: Cordless Drill Crank Charge Batteries
It gives a basic example of kinetic energy being converted into electricity, but for this application
the kinetic energy will be supplied by gravity instead of the hand crank.

The real fun with this project, I think, is the different ways that the kinetic energy of the weight can be harnessed. The screw used by the Gravity Lamp is just one method. A weight on a rope that is wrapped around a spool or crank is another option or even something based on the mechanism of a grandfather clock. One could even imagine a single massive weight that the whole family would hoist, with the help of pulleys, every evening to power their home lighting. Who knows.....

It's time to start a gravity revolution.


That link is already dead in 18 days after posting...
This is an 8 year old post and it is already out there by now. The YouTube channel SmarterEveryDay posted a video of a gravity light:

Whether it works or not, the roughly equal to one 40 watt incandescent lightbulb part is not good. I am starting to have difficulty reading at night behind a 60-75 watt bulb :-)


10 years ago

I had this idea a while ago, without realising it was a commercially serious idea. I envisaged a weight (probably a 25kg sack of salt) hung from the rafters of my garage on a rope wound round a crank, pulleys to gear up the crank it was turning to a bike dynamo powering task lighting for my workbench. Ultimately I intended to use a chainsaw ripcord ratchet so I could pull on a rope a few times to crank the weight back up to the top of its travel, but never got round to building that part so the system was a pain to use as it needed rewinding every few minutes.

Firstly, the numbers for how much energy you can extract from such a system assuming 100% efficiency. Let's assume that a small first experiment would use a 25kg (55 pounds) weight falling through 2 metres (6 feet 7 inches)

25kg * 9.8 N/kg = 245N weight
245N * 2m = 490J

Say you want an hour's power:
490J / 3600s = ~136mWh. I'd like to take this opportunity to state how much I love the SI/metric system :) Also note this is about 1/8 of the energy content of one rechargeable AAA cell, which doesn't sound like much.

136mW is about double the power consumption of a normal bike headlight (my first google result for "bike headlight LED milliwatt" reported 62.3mW), so this version could provide small task lighting or low level ambient for perhaps an hour once real-world efficiency is taken into account.

A larger version, with maybe a 100kg weight descending down the side of a house (from second floor ceiling height, roughly 6 metres) would provide 12 times as much energy, 5,880J or about 1.6 watt hours. Lighting a small-to-medium room can be done with a 12W CFL, so presumably about 5-8W of LEDs so even this fairly large system would only be able to light a room for a few minutes.

That said, I think this could be a very useful experiment which I whole-heartedly encourage you to try out. The numbers above have demonstrated that you can get an hour's usable light from a small system (2m, 25kg) and correspondingly more at larger scales. I'd suggest you find the materials for a system of this sort of scale, perhaps gut a cheap LED bike light and fit the LEDs in a desk lamp, and see how it goes. If you want to scale it up, maybe you could mount a larger system on an outside wall of your house? Alternatively, consider that lighting is a power hog- get a windup radio, a battery-powered desk fan or whatever takes your fancy, really. Maybe with the right voltage regulators etc. you could even charge your mobile from it?


10 years ago

Wait - wasn't the Gravity Lamp the design that was so over-hyped that it would have to break the laws of physics to produce as much light as advertized? As conceded by the designerafter winning 2nd place in a design competition...

To quote westfw from that discussion: It's sort of a sobering thought, that you'd have to carry that 50lb weight up something like 25 stories to get an hours worth of 40W light :-(

As for hand-powered generators, a more cutting-edge example would be Potenco's Latest Pull-Cord Power Generator ( Potenco is an offspring of Squid Labs, which makes it a... sister company to Instructables, I guess). Note how vigorously you need to pull that generator to produce a substantial amount of light.

I don't want to pour cold water on your enthusiasm (ok, well maybe just a little ;-). It is a good idea - otherwise companies like Potenco wouldn't be interested in it. But it's useful to check first how much physics says you can get out of it, rather than believing the hype.

It also points out how important energy conservation is, in comparison: if you can replace that 40W incandescent bulb in westfw's example with a 2W LED bulb, a hand cranked or gravity powered generator becomes a lot more interesting...

Of course I am going to use nothing but LEDs for the project and I am surprised that he didn't for his, I guess I just assumed that he did.

The "debunking" of the project DID assume LEDs at 4 to 8x more efficient than incandescent (5-10W output.) The proposed height and weight of the Gravity Lamp still came out 500x too small. :-( It wasn't just a little mistake that could be fixed with more efficient lamps; it was a BIG mistake. Even with 100% efficient gravitational potential energy to visible light conversion, it was orders of magnitude away from being useful.

Another interesting piece of inspiration is the Clock of the Long Now. Intended to keep accurate time for 10,000 years, but it was intentionally designed to require regular human winding of its two big drive weights, on the grounds that this would foster responsibility in its caretakers...


I was going to make a gravity generator, but never got around to it.