At perfect efficiency, this seems to give you about
55mW for a hour, if I asked Wolfram correctly (for
20kg lifted one meter) - [2] - So probably a hoax.
If you read some of the followups and tweak the math a little bit, it works out reasonably well. Instead of 20kg and 1m, 20lb and 2m, which comes out about the same (49.42mWh). If you have to lift it every half hour, that's 100mW for a half hour. That's more than enough power to get a useful amount of light out of an LED.
That's fine! It's enough to read a book or do homework after the sun sets. We're not talking first-world style lighting; we're talking about a $5 light that is better than sitting in the dark because you have no electricity and ran out of kerosene to burn.
It depends on the type of LED. Back when I was playing with them, Luxeons had a 180 degrees beam pattern while Crees were 70 degrees and neither had a built in lens like the cheap ones do (they used some kind of gel cover).
They really should consult some lighting experts or flashlight junkies to get the best bang for the buck.
I suspect it's even less than that. A fancy (= expensive!) bicycle hub dynamo has an efficiency of about 70%, and that's assuming that it's operating at peak efficiency, and that there are no additional mechanical losses in the lamp.
Um, please read the entire previous thread before dismissing this as a hoax. As you can see from a number of posts that I and others made there, the light is comparable to a kerosene lamp, which is what it's intended to replace. It is not, of course, comparable to the kind of light we in developed countries are used to, but that's not what it's intended for.
How many people can lift 30kg 2 meters up? How about doing it continuously?
You're also forgetting that it require human energy to power it, which requires food, which is usually more expensive than batteries or gasoline or kerosine.
Lifting 30 kg 2 meters requires about 600 Joules. If it takes 10 seconds to do it, using some kind of pulley arrangement, that's 60 Watts, which is not a strenuous level of effort for a human.
How about doing it continuously?
One 10-second lift every 30 minutes is not "continuously". Also, it would only have to be done when light was needed, i.e., during non-daylight hours when people were not asleep.
it require human energy to power it, which requires food
Humans require food whether they're lifting ballast to power lights or not. How much additional food would they require, if we assume that the entire energy required for the lights is added on (i.e., none of it gets shifted from other forms of exercise)? Let's see.
Suppose the light is in use for 4 hours a day; that means the weight gets lifted 8 times, for a total energy of 4800 Joules. One food calorie (which is actually a kilocalorie) is 4180 Joules. So we're talking less than 1.2 calories per day. What's that, an extra pellet or two of rice?
Because if you used a sufficient number to light a room you would have to hire people to lift the weights continuously, and if you have to to that, it would be far more efficient if you hired them to generate electricity using a pedal powered generator, because that is still the most efficient way to transform human labor into electricity.
Come to think of it, pedalling for the time it takes to lift the weight and charge a supercap that will them provide electricity to the LED might still be better.
[Edit: Lets do the math: 100W effective for 30 seconds gives you 3000J electrical energy stored in the cap, drained over 3600 second provides an average of 830mW for an hour.]
Like others have said, this is in no way a replacement for a pedal-powered generator, nor is it a replacement for a standing lamp. It's for folks in developing countries who would gladly trade lifting a pound or two of weight for 30 minutes of dim light.
Be cynical about the math, sure, but if the math works, don't assume technology is useless because it doesn't have a place in a 25 year old's San Francisco apartment.
A pound of two? We are talking about 50 pounds, every 30 minutes, for very dim lighting.
It's not being cynical to say "It doesn't work". Cynical would be to dismiss it without even checking. We gave it a full consideration, ran the numbers, and realized: It doesn't, and Can not, work.
The numbers don't show that; that's your subjective judgment based on the numbers. But the judgment that matters is not yours, but that of the potential users. It's up to them to decide whether this is better for them than a kerosene lamp.
I don't think its a hoax (I commented in the previous thread, initially skeptical but we worked out the math)
It may not be as useful as someone might like, which is to say you won't get a lot of light out of it. But unlike the candle example all of the light will be going roughly one direction. Think 'keychain LED flashlight' kind of light.
So in a place that literally has no light, it will be helpful. That last door in the dungeon, your village storage hut 30 miles from the nearest town on moonless nights. If you don't mind running the generator faster you can get brighter light for less time.
I took apart one of these [1]: http://www.amazon.com/FR160B-Microlink-Self-Powered-Weather-... which is Grundig crank powered radio/siren/flashlight. Its pretty bright, and you can power the LED off the internal generator directly. In fact if you were handy with some shop tools you could probably build your own version of this light with just this radio thing and mechanical connection between the crank and the weight. (You would leave the flashlight set to 'on') You wouldn't get 30 minutes of light, more like 2 minutes. But conceptually the idea is the same.
I like the design ethos of the 'clock' style energy source (I've got a grandfather clock that you wind by pulling up the weights on it).
I expect in a nominally lit urban environment it will provide little benefit. But that doesn't mean I believe it will be useless in all environments.
[1] I've now received 3 of these for 'free' (one as a conference giveaway, one came in a kit of earthquake supplies, and one was added into a garage sale purchase of other stuff. They kinda suck, in that they break pretty easily and once they do they don't work (internal wiring breaks). So finding a broken one shouldn't be all that hard if you're looking to experiment.
http://news.ycombinator.com/item?id=4889266
In that thread[0] revelation[1] said:
[0] http://news.ycombinator.com/item?id=4889426[1] http://news.ycombinator.com/user?id=revelation
[2] http://www.wolframalpha.com/input/?i=20+kilogram%E2%80%90for...