Gravity Lamp

About two weeks ago it was announced that a U.S. grad student, Clay Moulton, won second place in a "Greener Gadgets Conference" competition for inventing a floor lamp powered by gravity.

The concept was that a person would place a weight (about ten pounds) at the top of a four-foot column. Over the course of the next four hours, the weight would descend down the column, causing a rotor to spin that would produce a gentle light (about the strength of a 40 watt bulb).

Moulton's concept generated a lot of interest on blogs, but also a lot of skepticism. People who crunched the numbers insisted the thing could never work. It was outputting way more energy than was being put into it. But it seemed as if Moulton had actually built a prototype, and it did work -- and he had won an award for it. So the skeptics were kept at bay.

The skeptics were right. The thing would never work. Moulton has now admitted he hadn't built a prototype. It was just pie-in-the-sky theorizing. It would only work if super-efficient LEDs were invented at some point in the future. Or if you used a ten-ton weight. Moulton has offered to concede the second place prize.

The Gravity Lamp seems typical of so many of the inventions you read about that promise to save the world's energy problems. Somehow they never pan out. (via


Posted on Mon Mar 03, 2008


It's a great concept - but I think that people who go into a competition and submit a fake prototype are .. well.. pathetic.
I know it sounds nasty - but it shows that they only want to win, not put in the actual effort to get it RIGHT.
Though, I think that the judges didn't do a very good job if they didn't double check to make sure it wasn't a fake.
I do commend the guy for admitting his deception though.
Posted by sarahearth  in  New Zealand  on  Mon Mar 03, 2008  at  03:22 PM
With a weight of 5kg dropping from 2 meters you get E = mgh = 5kg * 9.8 m/s2 * 2 m = 98 Nm = 98 J = 98 watt second. i.e. if you have a 40watt light with 0% energy loss (from heat etc) it would light for about 2.45 seconds using the dropping weight as an energy source...
Posted by AAB  on  Tue Mar 04, 2008  at  02:59 PM
Using the guys weights and heights
m = 5 * 10lbs = 50 lbs = 22.67 kg
h = 58" = 1.4732 m
E = mgh = 22.67kg * 1.4732m * 9.8m/s2 = 327.294 J

With a 0% loss of energy 327 J lights up a 40w lightbulb for 8.18 seconds -or- over 4 hours you would be able to use a 0.0227 watt lightbulb.

A highschool physics student could have caught this as bogus.
Posted by AAB  on  Tue Mar 04, 2008  at  03:13 PM
So, you could get light from a dropping weight-- but not four hours' worth from a ten-pounder.

This energy source is not new-- my granparents had a cuckoo clock that was powered by two weights (probably a pound or two each) hanging from the bottom of the clock on long chains. The weights were shaped like large pine cones. My Grandma would "wind" the clock by pulling the free ends of the chains to raise the weights, then they would lower themselves slowly and turn gears as they went down. This would power the clock for about a week, inlcuding the hands, a swinging pendulum, and bird jumping out and saying "woohoo" every quarter hour.

Ah, I miss my Grandma.
Posted by Big Gary  on  Wed Mar 05, 2008  at  05:26 PM
Similarly generators could generate electricity from following water (water fall) from same concept.
The weight and height the guy describes in the competetion describes is just not enough to power a light bulb.
Posted by AAB  on  Wed Mar 12, 2008  at  12:06 PM
So he received his master's of science degree last year from Virginia Tech and created the lamp as a part of his master's thesis. Makes a Masters from Virg Tech sound a wee bit useless if they award them for nonesense of this kind. Don't the examiners bother to read theses these days before they award a degree?
Posted by Herman Zirmitz  on  Fri Mar 28, 2008  at  07:16 AM
Well, Herman, if he lied about the lamp he could have lied about having a degree.
Posted by Technically a Virgin  on  Fri Mar 28, 2008  at  07:20 AM
It looks as though he's a pukka student - see the link - Virg Tech seem pretty proud of him although they are somewhat apologetic about the lack of truth in the former report of this invention. The uni seem to believe that sometime in the future LEDs will be so efficient at converting electricity into light (several 100 percent efficiency) that this will work. This invention will never work as described. It might work on a planet where gravity is several 100 times stronger than on earth but then it would be difficult (probably impossible) for mere earthlings to even lift the 20kg mass on such a world.

The reality is that LEDs are already pretty efficient at converting electricity into light anyway and the improvements likely in the future are probably going to be only marginal and certainly will not increase it to more than 100%.
Posted by Philip  on  Sun Apr 06, 2008  at  01:58 PM
here's the link:
Posted by Philip  on  Sun Apr 06, 2008  at  01:59 PM

I don't think that even with a 100% efficient light source you could get this to work.

Consider that an ideal white light source for the human eye has an efficiency of 240 lumens/watt (

A 40 watt incandesent light produces 500 lu of light. Therefore a 100% efficient light source would require 2.08 watts of power.

Using the above 327 J (327 watts), you'd have a runtime of 157 seconds, somewhat less than 3 minutes.

And this guy is applying for a patent on converting potential energy to kinetic energy? It'll be interesting to see if the parent office awards it...

Posted by Lee Dilkie  on  Mon Apr 07, 2008  at  11:54 AM
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