You managed to get the right answer with the wrong math. It was 20 lbs for 2 meters. They talk about a run-time of 30 minutes, which would be about 100mW.
Kerosene has already been replaced; batteries are cheaper than fuel, and LED lamps are cheaper than kerosene lamps. The rest of this page looks pretty scummy; it says "780 million women and children inhale smoke which is equivalent to smoking 2 packets of cigarettes every day", which blatantly fails basic sanity-checking, and as others have pointed out the duration and brightness numbers for this don't add up either. So this is at best a well-intentioned but stupid waste of money, and at worst a scam.
> Around 3 billion people still cook and heat their homes using solid fuels in open fires and leaky stoves. About 2.7 billion burn biomass (wood, animal dung, crop waste) and a further 0.4 billion use coal. Most are poor, and live in developing countries.
> Nearly half of deaths among children under five years old from acute lower respiratory infections (ALRI) are due to particulate matter inhaled from indoor air pollution from household solid fuels (WHO, 2009).
the duration and brightness numbers for this don't add up either
They do if you're comparing it to a kerosene lamp; kerosene has certainly not been "replaced" in parts of the world that don't have easy access to batteries or electricity in general. See the numbers elsewhere in the thread. And it apparently does use an LED light.
I like the idea, but I dislike the "we'll distribute this for free" attitude. Distributing any kind of stuff for free has major economic impact, especially in poor countries where you replace or obsolete parts of the economy[1]. It's very common in the poorer parts of africa (Mozambique, Zimbabwe, ...) that people make their living of buying fuel at the gas station and reselling it by the liter for use in cookers and lamps or by collecting and selling wood.
A better way to go would be to validate the concept and find a way to produce the lamp and as much parts of it in the target communities, helping them to become self sustainable. The current idea just replaces local economy with earnings for a {american, european, chinese} manufacturer, effectively funneling funds away from the people that you want to help. So the goal is laudable, but I can't support the approach they're taking.
[1] other examples include food help which drives the local farmers out of business or donating clothes. Clothes often get sold for cheaper prices than the locally produced ones. Both may be useful in very specific circumstances, but are harmful in large scale.
You are right that the money will go out of the local economy, but this is not excuse for making better tools and technology.
For example I live in Europe, and when I get an iPhone... the money goes to the US, but this is not a problem as its technology and its an extra in my life.
But see when you have to buy basic things for living, like food, fuel etc... from non local companies its a problem.
Especially the poorness of Africa is deeper subject and i don't think that tools like that are the cause of it.
This thing can be applied my many more places that lacks electricity and its rather good than bad to have it.
Also, a wound-mainspring arrangement would be much more effective as a low-cost, practical third-world product. It would be lighter, less costly to produce, and would require much less space. This gravity angle looks like a gimmick, possibly to avoid infringing someone's patent.
When I was living in India last year, an Australian tech founder who rented a room in my apartment said we was tackling the kerosene problem too with solar. His company (Barefoot Power) wasn't highly technical, but rather put together components for an efficient solar powered light. The solar panel doubled as a mobile phone charger (phones are ubiquitous in India, even in the slums, so this was a huge selling point) and was enough to power the light for a full night.
I don't remember all the economics, but the cost of kerosene for x months would pay for the entire setup. Also, the light was an order of magnitude brighter than a kerosene lamp. But the interesting part (again, there's nothing highly technical here) was the business model.
It had a social/micro-finance bent in that he would source investors, who'd invest in shipping containers of these systems, which they'd sell on consignment to local entrepreneurs in poor areas. Those entrepreneurs would pay a fixed interest rate, so the investment was for-profit, and the local entrepreneur would profit from the rest. I remember him talking about building a Kiva-like interface where you could track your investment, right down to the shipping container, village and entrepreneur.
The best thing about this guy moving in was that my co-founder (of Flightfox) was just preparing for an expedition across the Gobi desert and needed solar power for her Macbook so she could blog about the expedition from the desert. All went well and she (Lauren) spent 52 days, trekking 1,000 miles, with full power and ability to blog over satellite the entire time. All using solar panels small enough to fit in a backpack.
That said, love the concept of the gravity light. For anyone who's spent a lot of time off grid, even dim light makes all the difference.
There's an interesting comment about super-efficient LED bulbs in that museum of hoaxes article. However, the numbers look marginal for this GravityLight even with super-efficient LED bulbs.
Quick back of the envelope calculation, using what few numbers are given in the article.
Ballast: m = 10 kg (1)
Height: h = 3 m (2)
Energy stored: E = mgh = 300 J
Time: 30 min = t = 1800 s (3)
Wattage available: P = E / t = 0.17 W (4)
Notes:
(1) Article says you can hang anything weighing about 20 lbs.
(2) No numbers given in the article, but the pictures make it look like ceiling height (8 to 10 ft., I took the larger)
(3) Article says light for half an hour.
(4) With current LEDs this is the equivalent of about a 2 W incandescent bulb, i.e., pretty dim. The light in the pictures in the article looks like the equivalent of about a 40 W incandescent bulb, so the numbers come up short by a factor of about 20. That would indeed be "super-efficient" for an LED; I'm not aware of any even on the drawing boards that are that efficient.
[Edit: The numbers actually are not too low compared to kerosene lamps, which are what this light is supposed to replace. See exchange downthread with xd.]
Perhaps, pretty simple to do the math though. Lets plug in some numbers and see what is what.
First we'll assume that the weight changes altitude by 2 meters, next we'll assume the "weight" is 5 kG (about 10 lbs) it could be more than that if you used denser material but it looks like they are expecting you to fill a sandbag to weight it dry sand is about 1600 kg/m^3 [1] so a sandbag that was 15cm/side would be about .0033 m^3 or 5.3 kg.
The force exerted by that sandbag, 2 meters up is 5 * 2 * 9.8 or 98 Newton-Meters. Now the campaign says it runs the light for 30 minutes so to find the power in watts we take 98 Newton-Meters divide by 1800 seconds (bag goes from 2m to 0m in 30 minutes) and get .0544 watts per second. Assuming the generator is 50% efficient (that is a really good generator) that is about .025 Watts to run your LED. So can you get decent light from an LED with 25 mWatts? At a forward voltage drop of 4V (White LED) that is 6.2 mA of current. (updated to be a decimal order of magnitude smaller)
Given that current LEDs are seeing something like 50 lumens/watt you might see 2 - 5 lumens from such a light. Not nearly as bright as I originally estimated.
Their claim is a 20 pound weight raised 6 feet (or so) in the air will generate light for 30 minutes:
20 lbf * 6 ft / 30 min = ~90 mW
For reference, the LED indicators on your keyboard use about 15 mW each. So that's about two keyboards worth of light.
However maybe I'm being stingy -- because of persistence of vision (a characteristic of the human eye), you can run LEDs (or any light) on a low duty cycle and still produce the same apparent brightness. So if we say they run it at a 10% duty cycle (I'm not sure how accurate this estimate is), they might be able to get closer to 1 W of LED light, which is enough for reading.
With perfect efficiency a 10 kg weight lifted 2 meters would only output about a tenth of a watt over half an hour. That is indeed enough for a led, but not a very powerful one. I doubt this is worth it.
Meta comment: I read the article and then did a back-of-the envelope calculation on how much energy you'd get out of one of these. Then I clicked through to the comments and saw that three other comments addressed this.
Good idea, but the physics doesn't work yet. A heavier weight might fix the problem, though. (I use a 5W LED lamp in my apartment that I keep on all the time. It's almost enough for reading and it's certainly enough for walking around at night.)
>It takes only 3 seconds to lift the weight which powers GravityLight, creating 30 minutes of light on its descent.
Why does every crackpot "revolutionary" energy gizmo make this same kind of nonsense claim? "Minute" is not a unit of energy, luminous intensity, or any other measure that is actually useful in evaluating the practicality of this.
Whether or not the device works - this usage of minute is also apparently unit of radio power or backlight luminosity, if cell phone makers and reviewers are to be believed. Declaring crack-pot status based on that usage is kind of over-the-top, unless you're here to argue that cellphones don't exist and are mere crack-pot theories as well.
Looks like the half an hour duration is only good for powering a LED at a small power.
The light seen in the video at the 55 seconds mark, shows the LED at full power and the weight drop speed is about 0.7 cm per two seconds (again, aproximately from the video), thats about 4-5 minutes for a meter of height.
Looks like the half an hour duration is only good for powering a LED at a small power
Yes, about a tenth of a watt (see the numbers upthread). However, that gives an LED light output that's comparable to a kerosene lamp. So it could be worth it for the target users.
Abbey Road studios was partly powered by descending weights when the Beatles were recording there. At the time, it was the best way to implement a constant speed motor for the price.
At larger scales, you are typically limited by the efficiency of whatever is lifting it. A large generator can convert kinetic energy to electric energy with very high efficiency (over 95%).
Also this is very poor energy density each kg moved 1m results in 9.8 joules or ~2.7e-6 kWh. So one metric ton moving 1km would generate 2.7 kWh.
I like the idea, but what kind of sick, twisted mind thinks it's a good idea to put the video in a player where they've disabled / hidden the controls?
[+] [-] revelation|13 years ago|reply
http://www.wolframalpha.com/input/?i=20+kilogram%E2%80%90for...
So probably a hoax.
(Wolfram fun fact: thats roughly the energy of the weight of a typical snowflake in oil (~4mg))
[+] [-] aidenn0|13 years ago|reply
[+] [-] guard-of-terra|13 years ago|reply
[+] [-] mistercow|13 years ago|reply
[+] [-] unknown|13 years ago|reply
[deleted]
[+] [-] jimrandomh|13 years ago|reply
[+] [-] DanBC|13 years ago|reply
(http://www.who.int/mediacentre/factsheets/fs292/en/)
> Around 3 billion people still cook and heat their homes using solid fuels in open fires and leaky stoves. About 2.7 billion burn biomass (wood, animal dung, crop waste) and a further 0.4 billion use coal. Most are poor, and live in developing countries.
> Nearly half of deaths among children under five years old from acute lower respiratory infections (ALRI) are due to particulate matter inhaled from indoor air pollution from household solid fuels (WHO, 2009).
etc etc
This isn't to say that the device is any good.
[+] [-] pdonis|13 years ago|reply
They do if you're comparing it to a kerosene lamp; kerosene has certainly not been "replaced" in parts of the world that don't have easy access to batteries or electricity in general. See the numbers elsewhere in the thread. And it apparently does use an LED light.
[+] [-] dzlobin|13 years ago|reply
[+] [-] Xylakant|13 years ago|reply
A better way to go would be to validate the concept and find a way to produce the lamp and as much parts of it in the target communities, helping them to become self sustainable. The current idea just replaces local economy with earnings for a {american, european, chinese} manufacturer, effectively funneling funds away from the people that you want to help. So the goal is laudable, but I can't support the approach they're taking.
[1] other examples include food help which drives the local farmers out of business or donating clothes. Clothes often get sold for cheaper prices than the locally produced ones. Both may be useful in very specific circumstances, but are harmful in large scale.
[+] [-] boksiora|13 years ago|reply
For example I live in Europe, and when I get an iPhone... the money goes to the US, but this is not a problem as its technology and its an extra in my life.
But see when you have to buy basic things for living, like food, fuel etc... from non local companies its a problem.
Especially the poorness of Africa is deeper subject and i don't think that tools like that are the cause of it.
This thing can be applied my many more places that lacks electricity and its rather good than bad to have it.
[+] [-] lutusp|13 years ago|reply
False, and the authors should be ashamed of themselves for posting this lie in a page meant to attract investors:
http://naldc.nal.usda.gov/download/38761/PDF
Also, a wound-mainspring arrangement would be much more effective as a low-cost, practical third-world product. It would be lighter, less costly to produce, and would require much less space. This gravity angle looks like a gimmick, possibly to avoid infringing someone's patent.
[+] [-] nostromo|13 years ago|reply
[+] [-] todsul|13 years ago|reply
I don't remember all the economics, but the cost of kerosene for x months would pay for the entire setup. Also, the light was an order of magnitude brighter than a kerosene lamp. But the interesting part (again, there's nothing highly technical here) was the business model.
It had a social/micro-finance bent in that he would source investors, who'd invest in shipping containers of these systems, which they'd sell on consignment to local entrepreneurs in poor areas. Those entrepreneurs would pay a fixed interest rate, so the investment was for-profit, and the local entrepreneur would profit from the rest. I remember him talking about building a Kiva-like interface where you could track your investment, right down to the shipping container, village and entrepreneur.
The best thing about this guy moving in was that my co-founder (of Flightfox) was just preparing for an expedition across the Gobi desert and needed solar power for her Macbook so she could blog about the expedition from the desert. All went well and she (Lauren) spent 52 days, trekking 1,000 miles, with full power and ability to blog over satellite the entire time. All using solar panels small enough to fit in a backpack.
That said, love the concept of the gravity light. For anyone who's spent a lot of time off grid, even dim light makes all the difference.
Edit: this system cost about $20.
[+] [-] cleverjake|13 years ago|reply
[+] [-] pdonis|13 years ago|reply
Quick back of the envelope calculation, using what few numbers are given in the article.
Ballast: m = 10 kg (1)
Height: h = 3 m (2)
Energy stored: E = mgh = 300 J
Time: 30 min = t = 1800 s (3)
Wattage available: P = E / t = 0.17 W (4)
Notes:
(1) Article says you can hang anything weighing about 20 lbs.
(2) No numbers given in the article, but the pictures make it look like ceiling height (8 to 10 ft., I took the larger)
(3) Article says light for half an hour.
(4) With current LEDs this is the equivalent of about a 2 W incandescent bulb, i.e., pretty dim. The light in the pictures in the article looks like the equivalent of about a 40 W incandescent bulb, so the numbers come up short by a factor of about 20. That would indeed be "super-efficient" for an LED; I'm not aware of any even on the drawing boards that are that efficient.
[Edit: The numbers actually are not too low compared to kerosene lamps, which are what this light is supposed to replace. See exchange downthread with xd.]
[+] [-] ChuckMcM|13 years ago|reply
First we'll assume that the weight changes altitude by 2 meters, next we'll assume the "weight" is 5 kG (about 10 lbs) it could be more than that if you used denser material but it looks like they are expecting you to fill a sandbag to weight it dry sand is about 1600 kg/m^3 [1] so a sandbag that was 15cm/side would be about .0033 m^3 or 5.3 kg.
The force exerted by that sandbag, 2 meters up is 5 * 2 * 9.8 or 98 Newton-Meters. Now the campaign says it runs the light for 30 minutes so to find the power in watts we take 98 Newton-Meters divide by 1800 seconds (bag goes from 2m to 0m in 30 minutes) and get .0544 watts per second. Assuming the generator is 50% efficient (that is a really good generator) that is about .025 Watts to run your LED. So can you get decent light from an LED with 25 mWatts? At a forward voltage drop of 4V (White LED) that is 6.2 mA of current. (updated to be a decimal order of magnitude smaller)
Given that current LEDs are seeing something like 50 lumens/watt you might see 2 - 5 lumens from such a light. Not nearly as bright as I originally estimated.
EDIT: The time was wrong 1800 not 180
[1] http://www.simetric.co.uk/si_materials.htm
[+] [-] colanderman|13 years ago|reply
Their claim is a 20 pound weight raised 6 feet (or so) in the air will generate light for 30 minutes:
20 lbf * 6 ft / 30 min = ~90 mW
For reference, the LED indicators on your keyboard use about 15 mW each. So that's about two keyboards worth of light.
However maybe I'm being stingy -- because of persistence of vision (a characteristic of the human eye), you can run LEDs (or any light) on a low duty cycle and still produce the same apparent brightness. So if we say they run it at a 10% duty cycle (I'm not sure how accurate this estimate is), they might be able to get closer to 1 W of LED light, which is enough for reading.
[+] [-] nohat|13 years ago|reply
[+] [-] trhtrsh|13 years ago|reply
[+] [-] jrockway|13 years ago|reply
Good idea, but the physics doesn't work yet. A heavier weight might fix the problem, though. (I use a 5W LED lamp in my apartment that I keep on all the time. It's almost enough for reading and it's certainly enough for walking around at night.)
[+] [-] pdonis|13 years ago|reply
And/or more height. The numbers are comparable to the low end of kerosene lamps as given.
[+] [-] mistercow|13 years ago|reply
Why does every crackpot "revolutionary" energy gizmo make this same kind of nonsense claim? "Minute" is not a unit of energy, luminous intensity, or any other measure that is actually useful in evaluating the practicality of this.
[+] [-] sophacles|13 years ago|reply
[+] [-] dexter313|13 years ago|reply
[+] [-] pdonis|13 years ago|reply
Yes, about a tenth of a watt (see the numbers upthread). However, that gives an LED light output that's comparable to a kerosene lamp. So it could be worth it for the target users.
[+] [-] stcredzero|13 years ago|reply
[+] [-] danso|13 years ago|reply
[+] [-] guard-of-terra|13 years ago|reply
[+] [-] IanDrake|13 years ago|reply
I think that'd be easy to fix though.
This has me wondering how much energy a larger scale application could store and what its efficiency would be.
[+] [-] aidenn0|13 years ago|reply
Also this is very poor energy density each kg moved 1m results in 9.8 joules or ~2.7e-6 kWh. So one metric ton moving 1km would generate 2.7 kWh.
[+] [-] guard-of-terra|13 years ago|reply
Hell, they should combine this thing with clock: a clock with weights that is also a lamp when needed.
[+] [-] Groxx|13 years ago|reply
[+] [-] boksiora|13 years ago|reply
[+] [-] rorrr|13 years ago|reply
[+] [-] pdonis|13 years ago|reply