Gravity Lamp Grabs Green Prize

eldavojohn writes "A lamp powered by gravity has won the second prize at the Greener Gadgets Conference in NYC. From the article, "The light output will be 600-800 lumens — roughly equal to a 40-watt incandescent bulb over a period of four hours. To "turn on" the lamp, the user moves weights from the bottom to the top of the lamp. An hour glass-like mechanism is turned over and the weights are placed in the mass sled near the top of the lamp. The sled begins its gentle glide back down and, within a few seconds, the LEDs come on and light the lamp ... Moulton estimates that Gravia's mechanisms will last more than 200 years, if used eight hours a day, 365 days a year." The article contains links to the patents and the designer/inventor Clay Moulton's site." I think my laptop would require a slightly larger weight to pull this off.

Comments

It can't possibly work either

[Maddog Batty]

22.6 Kg x 1m x 9.8 m/s^2 / 4 hours = 0.015W if conversion is 100% efficient (which it won't be)

The red led on the front of your modem requires around this amount so the glow will be feable. To get the equivalent of a filament 40W bulb requires around 10W so the system is only around a factor of 1000 out.

Re:It can't possibly work either

[Kijori]

22.6 Kg x 1m x 9.8 m/s^2 / 4 hours = 0.015W if conversion is 100% efficient (which it won't be)

The red led on the front of your modem requires around this amount so the glow will be feable. To get the equivalent of a filament 40W bulb requires around 10W so the system is only around a factor of 1000 out.

Your conclusion is right, but your figures are a bit out. The drop is 58" according to the plan. This gives about 0.022W at 100% efficiency.

For reference, the highest efficiency LEDs that I know of get 131 lumens per watt. If we're generous and allow them 150 lumens/watt, they still need 4W of power. This would require a drop of 255 metres using the 50lbs of weights he claims. Since we can't really go above 1.5m high, we'll need almost 4 tonnes of weights.

A shame really, I'd have rather liked one.

Re:It can't possibly work either

[Zalbik]

The drop is a screw so it's magnitudes more than 58".

And exactly how does having a screw generate more energy?

The path the weight takes to the ground is irrelevant.

An object weighing X lifted to a height of Y meters generates has a certain amount of potential energy, regardless of the path taken to the ground.

Re:Doesn't check out.

[retep]

Yup, they say it emits 600-800 lumens.

Given that LEDs emit about 100 lumens/watt, that's say, 6 watts, * 4 hours = 86,400 joules They claim it's about 2m high.

Plugging those two values into the gravitational potential energy calculator at http://hyperphysics.phy-astr.gsu.edu/Hbase/gpot.html gives a weight of about 5000kg, slightly above the claimed 22kg...

Physics for designers

[James McP]

You sir, are correct.

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. From memory really good blue LEDs are around 200 lumens/watt so .....3.8 lumens. A candle is ...13 lumens. So it's about a third of a candle. An ideal light source is ~680 lumens/watt would be 13 lumens, or a candle.

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.

Re:!perpetual motion machine

[steveo777]

Except that it doesn't. Do the math. One high output white LED needs 50mW for power.

Force x Distance/Time=W

22.6Kg x 1.47m x (9.8m/s/s)/14400s = .023mW

A brushless motor can operate at up to 90% efficiency, but the friction in the system will reduce the efficience a lot. We'll just say it runs at 60% efficiency. That's just 13.5mW. You need five of these to power an LED under current configuration. They want 600-800 lumens. So we'll lowball the figure with 600. Each LED can do about 80 lumens.

600/80=7.5, so 8 LEDs. That's 400mW of power for the system, or 30 generators.

Either you need 30 generators, a 680Kg weight, a 44.1m tall light (falling 30x's faster), OR a planet with 30x's the gravity. Your call.

Re:Why not use a spring?

[Kadin2048]

Probably could, but the overall lifetime of the device wouldn't be as long. Springs wear out over time, especially under heavy loads. The springs used in garage doors to assist you in pulling the door up (which were more common before everyone started installing power-operated doors) wear out after 10-20 years, for instance. I suspect each one of those springs -- there are typically 2 on a door -- each support 50 pounds or so.

I think part of the beauty of the mechanism is that it's really robust and long-lasting.

Just thinking about how you could build such a thing, I bet you could make a machine that had multiple ways of recharging/resetting it. My thought would be to have a lightweight 'sled' with a heavy removable weight on it. When the heavy weight is removed from the sled, a very small counterweight pulls it back up to the top of its track, so you can place the heavy weight back on. That's one way of resetting it, and the easiest provided you could pick up and lift the weight at once. The alternative would be to put a small crank on the sled's counterweight wire, which would allow you to slowly crank up the sled, with the counterweight on it. You'd end up doing the same amount of work but with a much smaller amount of force, due to the mechanical advantage of the crank.

That arrangement completely avoids using springs (it would only use counterweights) and would probably last a long time. I'm not sure whether it would be long enough to build some sort of 'Clock of the Long Now'-type device, but it would probably last a few human generations.

Re:!perpetual motion machine

[jridley]

Run the numbers before you get too excited. IMHO they're full of crap. They're claiming on the order of 175 times more power than they actually have. Either the weight should weigh 4000 kilograms, or it should be lifted 250 meters into the air in order to put out 600 lumens for 4 hours.

Re:Looks cool...

[Lumpy]

so why has he not actually built the thing?

because it cant be made. You have a better chance at making cold fusion work or a perpetual motion machine than making this lamp do what was claimed.

first, there is no way for them to make enough energy even assuming 100% conversion to generate the electricity needed to power even 1 led for enough light to match that of a book light, many others here have covered this fact already..

Secondly the designer made HUGE mistakes in assumption is is a fact being missed by everyone else here debunking it.. Led's when rated in lumens are rated in their very narrow beam pattern, when you fire it into a lens/reflector to disperse the light to get an area lighting effect that his lamp is going for the lumens drop logarithmically. to go from the 15Deg beam pattern the LED's lumen output is measured at to a 270 degree pattern you will lose about 80% of the lumen output level.

So to get The claimed output, the device needs to generate a SHITLOAD more power, or increase the weight to be near 900 pounds or only operate for a few seconds at a time.

In other words, it does not work, cant work, and will never work. I think the guy is waiting for the laws of physics to be broken for his lamp to work.

I have been working with a company that designs LED lighting systems and most everyone get's confused because ratings on LED's are all over the road and not measured the same way as other lamp technologies.

This lamp if it used CFL lamps would have a far better chance at makign the claimed Lumen output than with LED's led's are still far-far less efficient than CFL lamps when it comes to area light output in beam widths wider than 20 degrees.