Comments on: Gravia ‘Gravity Lamp’ lasts 200 years, doesn’t have power cord

By: Bob Brown

Bob Brown — Sun, 14 Dec 2008 00:10:54 +0000

sorry that is 200 million pounds

By: Bob Brown

Bob Brown — Sat, 13 Dec 2008 20:07:08 +0000

An aircraft carrier weighs 2 billion pounds(100,000 tons) How about putting it in dry dock and letting it fall about ten feet to generate energy?

By: Don White

Don White — Fri, 21 Nov 2008 18:14:46 +0000

I just had to comment because Larry’s comment cracked me up.

By: Larry Edelstein

Larry Edelstein — Thu, 21 Feb 2008 18:29:38 +0000

I can’t believe people fell for this bullshit. This little sociopath won an award, for chrissakes.

As if we lived in a world where we could get most of the power we need by occasionally running around and lifting shit off the ground.

By: Jay

Jay — Thu, 21 Feb 2008 08:01:13 +0000

Pay attention to Ian Calvert’s post above. His calculations are *very* generous and give an upper bound on output at 4 minutes.

Kevin: even if it engaged the motor while life the weights (which is not in the “design”), note that then *we* still have to provide that energy (and over the work required to lift the weight in the first place!) Thus, if the rotor applied an extra 23 kg of resistance to lifting, assuming 100% efficiency and a storage device (the design does have one) , you could double the life of the unit (to <8 minutes). Now your lifting ~100 pounds!

If you want to get that extra 54 minutes from these *very* generous calculations, the rotor would have to provide resistance of somewhere over 300kg, just a little beyond human capabilities.

In short, unfortunately some things just are too good to be true. Fortunately, we do still have stuff like human-powered flashlights – we just have to do actual *work* for that energy!

By: Martin

Martin — Thu, 21 Feb 2008 00:46:37 +0000

That kid doesn’t have to work anymore.

By: kevin

kevin — Wed, 20 Feb 2008 18:24:31 +0000

Ian, I agree with your calculations however maybe when you lift the weights the ‘rotor’ is still engaged and as a result you are doing more than using the potential energy of gravity. As you lift the weights, it turns the rotor and stores that energy as well?

Just a thought. See the design at
http://www.core77.com/competitions/greenergadgets/projects/4306/greener_gadgets_03.jpg

By: Ian Calvert

Ian Calvert — Wed, 20 Feb 2008 17:39:38 +0000

This thing doesn’t work. They claim 4 hours, but you’d be lucky to get 4 minutes.

This thing has a 23kg weight, falling 4ft, which gives an output of 270J, assuming 100% efficiency (!)
270J is 1W for just over 4 minutes. One watt for 600 lumens is also really, really generous. The best are in the region of 150 lumens/watt.