BKITU: "Kerosene lamps are problematic in three ways: they release pollutants which can contribute to respiratory disease; they pose a fire risk; and, thanks to the ongoing need to buy kerosene fuel, they are expensive to run."

Perhaps kerosene quality is erratic between different producers, leaving the consumers at risk of buying low-quality product. If only some young, enthusiastic entrepreneur could come up with a way of minimizing the risk of fire, maybe by creating a top-quality standard oil for home kerosene use... why he'd be richer than Rockefeller in no time!

He should be aware of this pesky by-product of the kerosene refining process, though. It's far too volatile to be used by the average consumer, but I bet he could find a use for it in running his refinery's machinery....

Threadjack away from cool gravity powered light, potentially starting a fossil fuel argument in just 2 posts. Not a record, but admirable.

Why not also set up a pulley system, bag descends at .2mm/second and gives 2.5 hours of light? Am I missing something here?

LesserEvil: Of course... the villagers will probably fill the bag with kerosene.

The snark is strong with this one...
[crowdclap.gif]

LesserEvil: Of course... the villagers will probably fill the bag with kerosene.

Don't be ridiculous. They will burn it for witchcraft.

This seems like the next logical step in the evolution of the "hand-crank generators". There have been lights and radios that run on hand cranked electricity for a while now. This is basically just adding a clock type mechanism to let gravity do the cranking.

Simple ideas are usually the best.

Strik3r: This seems like the next logical step in the evolution of the "hand-crank generators". There have been lights and radios that run on hand cranked electricity for a while now. This is basically just adding a clock type mechanism to let gravity do the cranking.

Simple ideas are usually the best.

Escape mechanism.

uksocal: Why not also set up a pulley system, bag descends at .2mm/second and gives 2.5 hours of light? Am I missing something here?

Now I want to go get a clock mechanism, crank LED flashlight and start playing.

Tom_Slick: uksocal: Why not also set up a pulley system, bag descends at .2mm/second and gives 2.5 hours of light? Am I missing something here?

Now I want to go get a clock mechanism, crank LED flashlight and start playing.

I think the pulley is replaced by the step up gearing inside used to spin a dynamo - same idea but using gears instead.

uksocal: Why not also set up a pulley system, bag descends at .2mm/second and gives 2.5 hours of light? Am I missing something here?

Yes---potential energy. E=mgh. Hoisting that bag of rocks 2 feet into the air is going to give you a set amount of potential energy. That energy can be used to power a very bright light for a very short amount of time, or a very dim light for a longer amount of time. Whichever you choose depends on your needs, but there will come a point where the light is too dim to be of any practical use.

Screwed kerosene vendors + Hired thugs targeting families that buy this = Not awesome.

Better than a crank-operated flashlight, because those typically still rely on rechargeable batteries, which wear out long before the light itself. I like this idea.

MadCat221: Screwed kerosene vendors + Hired thugs targeting families that buy this = Not awesome.

Yeah, who can forget the bloody Icebox Wars of the early 20th century, with hundreds of hapless refrigerator owners chopped into frozen cubes?

Wait a sec. The math isn't quite adding up for me.

Imagine a 2 kg bag falling 2 meters over half an hour.

The force on the string would be 2 x 10 = 20 Newtons.

The energy released would be 20 Newtons x 2 meters = 40 Joules.

40 Joules / 1800 seconds = 0.022 Watt.

Does anybody know of a two-hundredth-of-a-Watt LED that puts out any reasonable amount of light?

Ummm.... I'm calling BS on this one.

I could see this being nice for camping. Just use your backpack as the counterweight.

FTFA: Though it isn't clear quite how much light the GravityLight emits, its makers insist it is more than a kerosene lamp....Talking to Ars by telephone, Therefore's Jim Fullalove was loath to divulge details,

I don't think this is a bad idea, but between this and, you know, the math, it doesn't exactly pass the smell test. Not that the idea won't work, mind you, but it sounds like it's going to be pretty dim, and they're hiding that fact for marketing purposes.

A back of the envelope calculation: Using a 100 kg weight hoisted 2m up gives you 1960J. The article claims that the typical interval between lifts of 18 minutes, so you've got roughly 1.8 W available when the device operational, and 1.44 W if you spot them a very generous 80% conversion efficiency. The luminous efficiency of a cool white LED is approximately 10x that of an incandescent, so with this particular hypothetical setup, you're going to be getting light about as bright as your average 15 W bulb.

This isn't necessarily bad for what they want to use it for, but it may not be something that's going to wow investors. Furthermore, if they want to make it really cheap (i.e. plastic gears, generators without rare-earth magnets, no pulley system for raising the weight, etc.) a 100kg weight is probably out of the question, and the conversion efficiency is going to be much lower - the light output is probably going to be on-par or less than what you get out of one of those mini-Maglites.

Again, reducing dependence on fuel in remote areas is a good goal, but the way that this is being presented is really dodgy.

These guys use 20kg and say you can get useful light at around 20 milliwatts

Link

so I guess it's plausible... if not terribly practical IMHO.

cgs06: Wait a sec. The math isn't quite adding up for me.

Damn, too slow. No way they're going to be using a 2kg bag, though. A more realistic estimate, I'd guess, is probably around 10kg - any heavier and kids couldn't use it. But, as you say, the amount of light you're getting there is pretty negligible.

cgs06: Wait a sec. The math isn't quite adding up for me.

Imagine a 2 kg bag falling 2 meters over half an hour.

The force on the string would be 2 x 10 = 20 Newtons.

The energy released would be 20 Newtons x 2 meters = 40 Joules.

40 Joules / 1800 seconds = 0.022 Watt.

Does anybody know of a two-hundredth-of-a-Watt LED that puts out any reasonable amount of light?

Ummm.... I'm calling BS on this one.

Hey! It's all ball bearings nowadays. Now you prepare that Fetzer valve with some 3-in-1 oil and some gauze pads.

/Got nothing

errrrrm its a cuckoo........

"Coocoo"? Would it kill you to use a spell checker or Wikipedia?

cgs06: These guys use 20kg and say you can get useful light at around 20 milliwatts

Link

so I guess it's plausible... if not terribly practical IMHO.

It's not practicle for us (you wouldnt light your office with one) but if you choice is "sit in the dark" or spend 30% of your monthly income on kerosene to product the same feeble light, it's a slam dunk.

Martian_Astronomer: FTFA: Though it isn't clear quite how much light the GravityLight emits, its makers insist it is more than a kerosene lamp....Talking to Ars by telephone, Therefore's Jim Fullalove was loath to divulge details,

I don't think this is a bad idea, but between this and, you know, the math, it doesn't exactly pass the smell test. Not that the idea won't work, mind you, but it sounds like it's going to be pretty dim, and they're hiding that fact for marketing purposes.

A back of the envelope calculation: Using a 100 kg weight hoisted 2m up gives you 1960J. The article claims that the typical interval between lifts of 18 minutes, so you've got roughly 1.8 W available when the device operational, and 1.44 W if you spot them a very generous 80% conversion efficiency. The luminous efficiency of a cool white LED is approximately 10x that of an incandescent, so with this particular hypothetical setup, you're going to be getting light about as bright as your average 15 W bulb.

This isn't necessarily bad for what they want to use it for, but it may not be something that's going to wow investors. Furthermore, if they want to make it really cheap (i.e. plastic gears, generators without rare-earth magnets, no pulley system for raising the weight, etc.) a 100kg weight is probably out of the question, and the conversion efficiency is going to be much lower - the light output is probably going to be on-par or less than what you get out of one of those mini-Maglites.

Again, reducing dependence on fuel in remote areas is a good goal, but the way that this is being presented is really dodgy.

Honestly though, have you experianced the amount of light that comes from a kerosene lantern? a Mini-Maglites is at least as comparable to the output of the lantern. Honestly, I am thinking of donating $60 just so they will give me one for my 72hour emergency kit.

weiserfireman: Honestly though, have you experianced the amount of light that comes from a kerosene lantern? a Mini-Maglites is at least as comparable to the output of the lantern. Honestly, I am thinking of donating $60 just so they will give me one for my 72hour emergency kit.

My advice: Don't give them anything until they come back with a brightness spec. Or at least tell you how heavy the bag is.

WTF is a Coocoo?

LasersHurt: This light has been hotly debated re: whether or not it was physically possible, etc.

People began including calculations of the human power needed to raise the bag a few feet, however, and that's where the sensibility broke down and I stopped paying attention. Still, seems like it's easy enough to understand what goes on here.

I just did a back-of-the-envelope, and it does not look good. If you had a 10kg mass (which is kind of heavy) and 2m drop, you could get one tenth of a watt for half an hour. Whoop-dee-do. And pulleys won't increase the amount of work available from a given mass and a given vertical distance. They would allow a human to raise a heavier weight, but I don't think this gadget is equipped to take advantage of that.

pciszek: LasersHurt: This light has been hotly debated re: whether or not it was physically possible, etc.

People began including calculations of the human power needed to raise the bag a few feet, however, and that's where the sensibility broke down and I stopped paying attention. Still, seems like it's easy enough to understand what goes on here.

I just did a back-of-the-envelope, and it does not look good. If you had a 10kg mass (which is kind of heavy) and 2m drop, you could get one tenth of a watt for half an hour. Whoop-dee-do. And pulleys won't increase the amount of work available from a given mass and a given vertical distance. They would allow a human to raise a heavier weight, but I don't think this gadget is equipped to take advantage of that.

Looked up a random high-brightness LED. Looks like 20mA @ 4V can get you get ~4k mcd out of some of the ranks. So, so I guess. Not enough to light a room by our standards, but maybe enough to be useful.

pciszek: LasersHurt: This light has been hotly debated re: whether or not it was physically possible, etc.

People began including calculations of the human power needed to raise the bag a few feet, however, and that's where the sensibility broke down and I stopped paying attention. Still, seems like it's easy enough to understand what goes on here.

I just did a back-of-the-envelope, and it does not look good. If you had a 10kg mass (which is kind of heavy) and 2m drop, you could get one tenth of a watt for half an hour. Whoop-dee-do. And pulleys won't increase the amount of work available from a given mass and a given vertical distance. They would allow a human to raise a heavier weight, but I don't think this gadget is equipped to take advantage of that.

So you're looking at about 4-5 lumens which is in the range of a LED keychain light.- not very bright BUT then entire point is that the alternative for these people is paying 1/3rd of their monthly income for kerosene to make a flame not much brighter.

Yeah I wouldnt be comfortable hanging out in that kind of light but when sitting in the pitch dark is the alternative a 100% reliable and cheap source of light seems like something worth the effort.

Fizpez: cgs06: These guys use 20kg and say you can get useful light at around 20 milliwatts

Link

so I guess it's plausible... if not terribly practical IMHO.

It's not practicle for us (you wouldnt light your office with one) but if you choice is "sit in the dark" or spend 30% of your monthly income on kerosene to product the same feeble light, it's a slam dunk.

Exactly, you know how those Indiglo night-lights are basically crap, but once your eyes adjust to the dark they're pretty useful? Same concept.

I have one of the hand crank lights, and was able to survive in the Grand Canyon because of it when my other light died and I had 2 miles to go...

It isn't the brightest light, but it will let you see where you are going and who you are talking to better.

It is an interesting concept, but I'm not buying the 2m (6ft) drop and 18 minute part. If I hand cranked a light, it would pull up the 2m string in 30 seconds to get a decent amount of light. You would need something like a bicycle gear ratio to slow down a heavy bag over the 18 minutes. Not that I couldn't be proven wrong though, and it is a worthwhile experiment. It is what high school and college physics students should be working on and designing...

boohyah: errrrrm its a cuckoo........

Thank YOU!!@! came here to say this! Way too many posts before someone had the courage to say this! Seriously, people.

/ Why haven't the grammar and spelling nazis descended on this thread by now?
// Wasn't Coocoo a character in a movie of some sort?

Normal: I have one of the hand crank lights, and was able to survive in the Grand Canyon because of it when my other light died and I had 2 miles to go...

It isn't the brightest light, but it will let you see where you are going and who you are talking to better.

It is an interesting concept, but I'm not buying the 2m (6ft) drop and 18 minute part. If I hand cranked a light, it would pull up the 2m string in 30 seconds to get a decent amount of light. You would need something like a bicycle gear ratio to slow down a heavy bag over the 18 minutes. Not that I couldn't be proven wrong though, and it is a worthwhile experiment. It is what high school and college physics students should be working on and designing...

pendulum/escapment

Everyone knows about a weight-powered device. I have one in my home. It's called a Grandfather clock. (Or cuckoo clock.) Like he said, you need high friction for a gear-based mechanism to work, otherwise the weight accelerates on the way down. Bad for a device like this because the friction loses valuable energy. The escapement (or grasshopper) prevents that, and the pendulum controls the speed. I suppose there might be a safety issue with a 20 pound weight six feet high combined with a fast and/or heavy pendulum. It wouldn't be remotely feasible without a low-power/high efficiency LED.

But why keep it secret? People are going to take them apart anyway to see how they work. And if you want to help starving Africa, you would make this open source hardware.

/ Yes. I am aware of the headline. That's the joke.

cgs06: Wait a sec. The math isn't quite adding up for me.

Imagine a 2 kg bag falling 2 meters over half an hour.

The force on the string would be 2 x 10 = 20 Newtons.

The energy released would be 20 Newtons x 2 meters = 40 Joules.

40 Joules / 1800 seconds = 0.022 Watt.

Does anybody know of a two-hundredth-of-a-Watt LED that puts out any reasonable amount of light?

Ummm.... I'm calling BS on this one.

Oh look it's one of these guys..

StoPPeRmobile: Strik3r: This seems like the next logical step in the evolution of the "hand-crank generators". There have been lights and radios that run on hand cranked electricity for a while now. This is basically just adding a clock type mechanism to let gravity do the cranking.

Simple ideas are usually the best.

Escape mechanism.

Wouldnt need/want one. that would stop the motion, on a regular basis, you want a continuous even motion. I could see gears and a flywheel, but not an escapement,

SomeTexan: Like he said, you need high friction for a gear-based mechanism to work, otherwise the weight accelerates on the way down. Bad for a device like this because the friction loses valuable energy.

WAT

The mechanism is doing work against a generator. Why would you want friction (which dissipates energy as heat), instead of converting that energy to electricity, and thence to light?

jfarkinB: SomeTexan: Like he said, you need high friction for a gear-based mechanism to work, otherwise the weight accelerates on the way down. Bad for a device like this because the friction loses valuable energy.

WAT

The mechanism is doing work against a generator. Why would you want friction (which dissipates energy as heat), instead of converting that energy to electricity, and thence to light?

You missed the point. Friction is *Bad* but you have to have it with gears only; otherwise it accelerates.