In a display of the awesomness of the Internet, users of the website Slashdot have thoroughly debunked claims made by the inventor of the Gravia gravity lamp. The inventor claimed that the lamp could use a 50 lb weight dropping five feet to power a 700 lumen LED for 4 hours.
But when the Slashdotters actually did the math, they discovered a few flaws. First, the inventor assumed 100% efficiency.
Much worse, is that they seem to have put a decimal in the wrong place, and ended up with completely erroneous numbers:
There's 50lbs of weight that fall about 4ft, if I'm reading the diagrams right. That's 200 ft-lbs. Which comes out to... hmm... 0.075 watt-hours. Over 4 hours that means 0.019 watts continuous power.
To get ~700 lumen light at 200 lumen/watt would require 3.5 watts of power, over 4 hours is 14 watt-hours or 3700 ft-lbs. Over 4ft of fall that amounts to 925 lbs. My goodness, that is a group effort.
written by nickjohnson, February 23, 2008
written by Mark Bartosik, February 25, 2008
written by Reg, March 19, 2008
|< Prev||Next >|