# Gravity Lamp Calculations

http://www.core77.com/competitions/greenergadgets/projects/4306/

some people might recognize this little invention a while ago. Well I recently wanted to make one after a freak snow storm rocked central pennsylvania (didn't have power for 2 days, it sucked balls). But, after doing the math, his claims seem impossible. Someone check the math for me:

Facts of the Gravity lamp (with data in favor of the lamp_:

output: 600 lumens

weight falling: 50 pounds

distance falling: 58 inches (in reality it's a bit shorter, but i'm just putting everything in favor)

for ease of calculation and in favor of the lamp, assuming 100% efficiency.

lasts for 4 hours

calculations:

600 lumens = 7542 candellas = 7542000 mcd

the highest efficient LEDs i could find output 120,000mcd at 20mA (0.02 amps) with a drop of 3.2 volts

7542000mcd/120000mcd = 63 LEDs

1 LED = 3.2 volts * 0.02 amps = 0.064 watts

63 LEDs = 4 watts

50 pounds = 22.68 kg

on earth: the force of the weight is 22.68*9.8 = 222.264 newtons

58 inches = 1.47 meters

1 joule = 1 watt * 1 second = 1 newton * 1 meter

222.264 newtons * 1.47 meters = 326.73 joules

326.73 joules / 4 watts = 81 seconds, NOT 4 hours

looking back at it, I think i messed up the calculations at earth's gravity, because that part is just totally wrong :P. I'm not far enough into my physics class to know how to properly calculate that, could someone else?

## Discussions

I'm kinda mad that all these people praised his invention as "genius" and stuff.

A couple of days after he found internet fame he confessed it wouldn't work inless super efficient LEDs were invented :P

at absolute 100% efficiency of 683 lm/W, you could achieve 372 seconds of light, yeah... this guy definiteley could see this thing in the future, with more efficient LEDs... rightt... except it still falls almost 40 times short of the goal!

That's easy to fix...just use a 2000lb weight.

yeah, but i don't think your mom will like being the weight for 4 hours

jkjkjk, haha

here's my new idea, lets say the average person weighs 160 pounds, and if they go up a flight of stairs, they must come down. If they were on a sort of elevator on the way down, they could power the lamp for almost an hour! that is, of course, with 100% efficiency

A modified stair-lift?

L

You could still do fun things with it, like power LEDs that would glow as you descended...

Haha, that'd be intense! Then again, I don't trust myself enough to build something that's like 10-15 feet off the ground :P

10-15 feet? Goodness, how high are your floors?!

Inventors don't become rich and famous, marketers become rich and famous.

Yeah, this thing has been debunked at least twice in the forums, search gravity lamp. I think Westfw did the calcs already.

I get similar results. But the <em>design goal</em> of this is to do that. Rather like this thing:<br /> <a href="https://www.instructables.com/community/hplb-ratio-201/">www.instructables.com/community/hplb-ratio-201/</a><br /> <br /> L<br />

ah, okay, kinda skipped over the word"goal" in the article :P

still, when the goal is to produce 180 times the energy put in is a pretty bad goal :P, totall impracticle

Well yes. But it got your attention and some more page-hits...

L

I agree with your maths, within a few insignificant decimals.