In that thread revelation said:
At perfect efficiency, this seems to give you about
55mW for a hour, if I asked Wolfram correctly (for
20kg lifted one meter) -  - So probably a hoax.
For example, this LED uses 68mW https://www.sparkfun.com/products/531 and is marketed as "so bright that it hurts to look directly at them"
They even include a photo of the beam pattern - it's almost as focused as a laser.
(You can tell on an LED by looking a the top - round tops are focused, flat ones spread out.)
They really should consult some lighting experts or flashlight junkies to get the best bang for the buck.
A simple wax candle produces 11 lumen. And there is no way you will get anywhere near perfect efficiency.
So at best, this will product maybe 1/3 of the light from a candle.
If you directed that light into a small spot, it could be useful, but of course it's a large device and you can't do that.
If you illuminated a room with it it would be enough to walk around and not crash into things, but not enough to read.
Another comparison: Assuming a 2 meter by 2 meter room (which is tiny), this would produce 1.3 lux (again, assuming perfect efficiency).
Moonlight produces betwen .25 and 1 lux.
So at best, with reasonable efficiency, and assuming a tiny room, this is comparable to moonlight under a full moon.
Can you read in moonlight? Go try.
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?
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.]
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.
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.
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 : 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.
 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.
EDIT: Apparently people don't understand that using gravity to generate energy is a thing, and the title "Powered Solely" suggested someone found a way to do that.
The machine converts gravitational potential energy to electromagnetic radiation. People generate the gravitational potential energy by lifting the weight using kinetic energy, which was likewise created by converting chemical energy.
It's easier just to say "Gravity" because, without gravity, it wouldn't work with its inanimate weight.
Actually, it does, and that's the perfect way to analyze this. Food is good for keeping humans alive, but it's a pretty foolish fuel to burn in a human engine to accomplish things. It's perishable, it's eaten by rodents, it's hard to transport, and more. I chuckle darkly when someone tells me that something is "green" because it's human powered. Growing food isn't free - it uses conventional energy sources to harvest, transport, etc., and it's a ton less efficient than just burning that fuel directly.
The ingredients needed for fusion on the other hand are thought to have been created during the some of the early stages of the Big bang so fusion is truly independent of stars.
At any rate, the phrase was written by Enpundit, not GravityLight. Their indiegogo page is less dramatic and more scientific about what powers their lamp:
You wouldn't do it for $5 though. Efficient Stirling Engines with a reasonable amount of torque actually require significant engineering, and that comes at a cost. However, they wouldn't require significant maintenance, they would provide power all the time that could be stored (again, at a cost), and might be able to trickle power an entire village.
Yes, Stirling Engines can be wonderfully efficient, and they are a delight to watch in action. Lovely machines.
Shouldn't it be said that it is powered by vacuum energy, since that is what kicked of the Big Bang? (And, before anybody tells me I'm wrong, let me say, "I'm wrong!" Instead of telling me I'm wrong, educate me. I love learning about this stuff, and I know my knowledge is weak.)
But if you ask me, it's always at the low end of things - like this project - where the really inventive, exciting engineering happening.
Sure, something like an F1 car is impressive after a fashion, but considering the price, yeah, well, it better knock my damn socks off or it just looks stupid. Unlimited budgets do not make for impressive engineering, really.
Making something that is truly, spectacularly useful like this for $5 ot $10? That is genuinely impressive.
That's why I got into the demoscene. While I'll drool over the crazy new demos pushing the latest GPUs to the limits, it's always more impressive to me when people take extremely limited systems and file sizes and do incredible things with them.
Not sure where this came from -- Douglas Adams, maybe?
also, a quick plug for my blog [http://aleverlongenough.wordpress.com/] rounding up projects like this - it was unfortunately short-lived because life got busy, but i hope to restart it in 2013.
The best way to provide lighting and clean water is via the grid: power lines and water pipes.
Also, with clocks, you get to skip the conversion of the energy completely. That immediately gets you a much higher efficiency than this lamp, which is potential energy converted to electricity (losing heat), converted to light (losing heat). Of course energy transmission losses still apply, ie. it's not free to get the mechanical energy from the spring to the hands of the watch.
Flywheels have a lot of engineering hurdles that can't be met for $5:
- they need to be well-lubricated, clear of dust (which I imagine to be a problem in some of the environments they're trying to sell to)
- they need to be perfectly balanced, or the shifting center of gravity will vibrate the housing - sapping away precious energy.
- they need to run at high, ever-decreasing speeds, which means generators that can extract a constant power level at different speeds
I have a hard time seeing myself using something like this, except as task lighting. I'd be fine to have to lift a weight if I was only going to be using the kitchen for 30 minutes (it could even serve as a useful timer), or similar. But getting up every 30 minutes rules out using it anywhere I need longer duration light for eg, reading.
Also, anywhere I could use this, I could use any of the many inexpensive crank LED lamps available everywhere, which run for similar amounts of time.
The pity is that, with the right design, this could support a longer cord for a further lift distance, so it'd run an hour. Or multiple weights used in sequence or parallel so it can be primed for even longer (iirc that's how my grandparent's cuckoo clock worked). From what I can see, it's not designed to be very hackable, and something like this needs hackability.
The LED light is the other problem with it; I'd much rather have a well ventilated kerosine light than blue tinged LED for almost any task. (I'm curious to see studies about kerosine health risks however.) Since this light cannot be moved, it has to illuminate the whole area, and its light doesn't seem up to it, so I'd be doubtful about eg, reading by it either.
It's not just that, it's also extremely polluting (both for the immediate and greater environments) and dangerous. The kerosene isn't the most expensive part, it's buying a good quality lamp that won't tip over or leak toxic gases.
Not sure if I should patent this, or just donate it to the greater good of mankind.
Technically powered by the sun.
Technically shut up with useless pedanticism.
On the other hand, your "if you're reductive at all, you have to be 100% reductive all the time or shut up" argument is completely unhelpful.
It's powered by a human lifting the weight.