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GravityLight: Generate light with gravity (gravitylight.org)
384 points by dimitrideag on July 31, 2015 | hide | past | web | favorite | 126 comments

There's a lot of reasons why this is cool, but I'm skeptical about it's aims to get rid of kerosene lamps.

Kerosene lamps are made with garbage. They can be replaced in minutes if there's a problem. Fuel costs are high, yes, but capital costs and maintenance are low. Those matter.

To really make this a long term win, you need to make it indestructible and easy to repair with on-hand parts. I hope they can do that.

It looks like they are trying to make them in a locally sustainable manner...

>We're doing this in our approach to distributing GravityLight

>We are partnering with local networks of people earning a living by selling products such as GravityLight, rather than disrupting local markets and jobs with free giveaways.

>We're doing this in our manufacturing strategy

>We aim to create jobs and skills in the regions where GravityLight will be sold, firstly by establishing an assembly line in Kenya.

from http://gravitylight.org/our-approach-3/


And it looks like they've already run into robustness issues, but they weren't due to cheap plastic components, and it looks like they've modified the system to deal with them...

>GL01 had a protection mechanism that clearly indicated an overload with a red light, and helped reduce damage to the gear teeth by allowing it to run more swiftly, but this did not make it indestructible. An entirely novel way of protecting the system has been designed for GL02. It will allow an overloaded bag to descend to the ground in a safe and controlled manner, repeatedly.

>GL02 suspends the bag from a pulley, which reduces the strain on the cord and the gearing. This also decreases the loading on the drive system and permits a smaller gearbox ratio, which helps to improve efficiency.

from http://gravitylight.org/coming-soon-gl02/

> To really make this a long term win, you need to make it indestructible and easy to repair with on-hand parts.

That was the first thing I looked for. The materials, at least from this image, look plastic and very custom made. http://static1.squarespace.com/static/552aca94e4b0c75f5b87b0... If these parts get brittle and break/crack, how are they repaired?

I can see that potentially being a problem, especially if dirt or something gets caught in it. However, the most delicate part of it is the most replaceable, that band could be easily made out of cloth or leather, and motors are usually fairly available. It's most certainly a better argument than "it's not much power" etc, but I'm not convinced it matters too much. I doubt just as much as the next guy these things will change the world, but it's a noble idea and a noble purpose.

Yeah this seems to be a big issue just by looking at it and makes me wonder why they didn't use everyday parts like a chain or a sprocket off a bike.

Also I wonder if you could just do all this with a refitting of a rachet lever hoist or something similar.

Maybe folks over there keep a kerosene lamp and a night's supply of kerosene on hand just like we keep candles, flashlights and batteries handy.

I implore people to support something far more practical like http://www.solar-aid.org/ than this.

Solar lights are many times more thermodynamically efficient, cheaper to make, smaller and much more robust (no moving parts!).

This "lifting weights" thing is a silly gimmick. A lifted weight stores a miniscule amount of energy compared to a battery that's been charged by the sun.

Don't both have their places? There are benefits to having a power source that is a) not dependent on a resource that is not available at all times and b) does not require a charging period.

It's sort of like people in the late 19th century saying you shouldn't support the development of automobiles, because boats are much more efficient way to move cargo. While true, it does nothing to address the fact that in some cases the use of a boat makes no sense, such as transporting to a land-locked location.

"Don't both have their places?"

It's more that this "invention" has been bouncing around for a while and gets an unwarranted amount of attention for the amount of energy it can provide. Weird to think, but solar isn't "sexy" in the same way.

"D'oh, we forgot to charge our solar light earlier today."

"No worries, we'll just use the gravity light for now."

That scenario seems reasonable to me. The point is not the amount of energy the technique provides. The point is the utility people get out of it. And I see a place for both; GravityLight and Solar Aid seem like great projects.

I think they would be good in a mine safe room or something, no need to ever replace batteries right. There are a bunch of cases you might not have a charged light.

Maybe that "unwarranted amount of attention" is because it has a different set of requirement for use than solar which makes it particularly attractive. Considering only the energy efficiency and not how it could or would actually be used by the target consumers seems shortsighted to me. It may yield a the most efficient product, but it may not yield the most effective product.

Yeah, sure, but that set of requirements is, I'd argue anyway, probably more appropriately served by something clockwork or something crank-based that charges a battery.

exactly boats are still used when an automobile can't. Just the same as in low light areas, gravity is your only option. Plus I think gravity is probably a cheaper solution to offer, as the weight can be used from local resources while a solar panel is an added cost.

Gravity is not the only option.

This isn't a boat with oars. This is a boat where you're given some wooden spoons.

Coal and kerosene are cheap.

We need to stop dicking around with idealistic ideas involving electronics and design more efficient and safer uses of these existing cheap fuels for lighting and more importantly cooking and phone charging.

They are being used because they work for people in these situations.


> Solar lights are many times more thermodynamically efficient, cheaper to make, smaller and much more robust (no moving parts!).

Beyond the "no moving parts" (and maybe cheaper to make), I think you're just spilling a marketing blurb.

> This "lifting weights" thing is a silly gimmick. A lifted weight stores a miniscule amount of energy compared to a battery that's been charged by the sun.

Potential energy = m.g.h So, lifting a 10kg weight at the height of one meter gives approx. 98J

Incident solar power is 100W/m2 (best case). A square solar cell 10cm of side hence gets 1W (or 1J/s), after efficiency losses this is even less (which are present on the GravityLight as well). Between 0.5W and 5W seems common on sale websites

So, lifting the weight above (which takes 1s approximately) gets you as much energy as 36s of solar energy (of course, you can't recharge it at night)

Also consider the cost of the battery

Edited for wrong math

There's a running joke among cantonese who've watched the comedy 國產凌凌漆[1] (= Domestic-produced 007), the character who acted as Agent 007's inventor, built for the agent a solar-powered torch that only works in the sun. Thanks for the chuckle.

[1] https://en.wikipedia.org/wiki/From_Beijing_with_Love

The weight option has the benefit of durability. A battery needs to be replaced after x charge/discharge cycles. The goal of GL is to reduce poverty cycles by making a one-time investment that pays for itself in a month. Adding the recurring cost of a battery, even if still cost effective, runs counter to that goal.

The weight option has lots of moving parts under tension from about 10kg of weight hanging off the mechanism. That's going to present its own durability problems, and the parts are going to be a lot harder to obtain and fit than a new battery.

The inuit people cannot use solar. I think that it is better to have both solutions in the field and the time will tell which solution is better for a given region.

Your comment is a mixture of the irrelevant and the incorrect.

First, you’re mistaken about the robustness of batteries. Batteries tend to have a very short lifetime, measured in months to years, and they can typically only be recharged a few hundred times. Generators have longer lifetimes, measured in generations to centuries. Batteries are usually a lot cheaper than generators, so it might make sense, as you say, to just replace the batteries a few times. But how much does a 100mW generator cost? Amazon is selling an “X Factor” brand 3000mW generator along with accessories for US$17.56, so I suspect that the retail cost of a 100mW generator would be about US$1. (Little 1-watt brushless DC motors do cost about US$1 to US$3. I can’t find any 0.1-watt DC motors.) By comparison, the retail cost of an 800mAh AAA NiMH battery (3700 J, 1000 charges, thus lifetime about 3–5 years, Tenergy Centura brand) is about US$1.50 to US$2.

Second, it is incorrect to say, “A lifted weight stores a miniscule amount of energy compared to a battery,” except according to irrelevant figures of merit. Batteries do indeed have orders of magnitude higher energy density per kilogram and per liter, about 400kJ/kg and 1MJ/ℓ, while a bag of sand that has been lifted two meters only stores 20 J/kg and something like 20 J/ℓ. But those are not relevant figures of merit here. The target audience has tens of thousands of liters of available storage space, even in the worst slums, and can store tons of material, and the target application only needs to store 120 J. Reducing the weight of the stored energy from 6 kg and 6 ℓ down to 300mg and 0.12 mℓ (or, more realistically, 4g and 2mℓ, since you need to store more than 20' of energy) is not needed to replace a kerosene lamp; it provides you with a flashlight. Not to say that flashlights and solar lights aren’t useful, but if this is cheaper than a flashlight, maybe it’s useful anyway. Solar lights and rechargeable flashlights cost about US$6 to US$10 at retail today, which is a significant amount of money to a lot of people.

It’s true but irrelevant to say that lifting a weight by hand is not particularly thermodynamically efficient. It’s incorrect (but still irrelevant!) to say that solar lights are more thermodynamically efficient. Lifting weight is about 25% efficient, due to the inefficiency of your own muscles. (Generators are typically better than 90% thermodynamically efficient.) This is substantially more thermodynamically efficient than solar lights, which lose 85% of the sunlight on input and another 50% or so in the battery. If you can get the energy from somewhere else, rather than muscle power, then the weight is many times more thermodynamically efficient.

The efficiency question is irrelevant because we’re talking about 120 joules of energy for 20 minutes of light, which is an amount of energy that costs US$0.000003 if you have an actual power grid, or 0.03 grams of carbohydrate if you’re powering your 25%-efficient muscles (between one and two grains of rice). The only people who worry about conserving the energy in individual grains of rice are people currently experiencing a famine, mentally insane people, and commenters on Hacker News.

The one thing in your comment that might be true and relevant is the statement that solar lights are cheaper to make, because we don’t know how much the final retail cost of these Gravitylight gizmos will be. However, it seems implausible that they are many times cheaper to make. It seems likely that the vast majority of the cost in either case will be non-electromechanical components like the plastic housing, the gear train, glass or plastic to protect the solar cells, marketing, and so on, so the two solutions are likely to be almost exactly equal in cost. One will be portable but need to be left out in the yard to charge; the other will be heavy and nonportable, but you’ll be able to charge it in the middle of the night.

Years ago there was a similar 'potential energy to electricity' buzz and I was initially quite excited. Then I did the math on how much energy is actually available (even at 100% efficiency) from such a scheme. Spoiler - it's minuscule.

E = mass x 9.81 x height

So a 10kg mass at 2 meters can (@ 100% efficiency) provide 196 joules of energy. A modern cell phone battery has about 25000 joules. To charge said phone would require raising that weight well over 127 times.

Hmm, that's actually pretty doable if coupled with pedal power (you'd either charge directly with a dynamo in this case or pump water to a higher elevation to store as potential energy). Back of the envelope math says you could do it quite easily in 15 minutes which isn't bad at all especially given the fact that you can't shove power into the battery anywhere near that fast.

Granted, this works much better with something like a light because LED's use so little power to run.

Pedal-powered generators already exist. Using one to charge a battery is better than this gravity-energy-storage gimmick in every imaginable respect, but they still are not used much, because electricity is not scarce. (If you can afford to buy a gimmicky generator, you can afford to buy a real one instead and the real ones are cheaper and better.)

That's pretty fair.

But this isn't for charging a phone; it's for having light, right now.

1 watt of led light would require 1 Newton at 1 meters per second. Assuming 100 kg is the highest practicable mass, so that's 1000 Newtons -> 1/1000 m/s for each watt. Assuming a height of 2 meters, you could operate a very dim 2 watt led light for 17 minutes. I think that's not practical.

Or, using the numbers provided for this actual product which exists, rather than a spherical LED on a frictionless plane, we raise a 12kg mass 1.8m and get a 0.1W LED light for 20 minutes. Do you think THAT's practical?

0.1W LED light is as bright as one of those clip on book reading lights, they only look bright in pictures. It's not quite useless, but you can build a 0.1w for 12 hour solar light with a 12' cord for ~2$ making the whole thing a joke.

Ok, I confess to not reading the article, I was just reacting to the comment. That actually starts making a lot of sense.

You can use it to read and it is free.

It's not free. It's a very inefficient way of converting food to human energy to humans lifting weights that in turn power the lights.

If this is targeted at very poor people, food isn't cheap for them.

If you think about the methods of farming worldwide etc, they also use a lot of human labor etc because there's not enough sophisticated industry to run everything on solar charged battery powered robot tractors... So you have to accept a local optimum.

Reading for half an hour per day could have large payoff, compared to reading very little ever, because it's too dark.

Neither is kerosene. Many people reply based on their gut feeling, but that doesn't mean it lines up with reality. A chocolate chip cookie has enough energy for a person to go jogging for 20 minutes. No one is going to starve to death by lifting a weight every 20 minutes for a few hours at night. They might be able to lift themselves out of poverty if they stop paying for kerosene and read (or learn to read) in the time that they aren't working, which is likely at night.

The energy involved here is between one and two grains of rice.

I get it, I am just saying that there are a lot of ways to make a single LED light shine, potential energy from a weight is likely the least sensical.

> potential energy from a weight is likely the least sensical.

potential energy is very easy to produce, keresene is not always available. I think this is the #1 benefit.

The key here is that this method does not require a battery. In practice though I am skeptical that this contraption would live much longer than a rechargeable battery combined with something more versatile such as a hand crank.

For comparison, that's in roughly the same ballpark as the amount of energy one of the tiny, cheap rechargable batteries in a dollar-store solar light can store. Potential energy just isn't all that viable.

You could theoretically have something like a 1000kg mass which was lifted through a series of pulleys...

what lifts them?

A human does.

Also assuming 100% efficiently, 196 joules is enough to run a 1W LED for 196 seconds (3:16), or a 0.1W LED for 1960 seconds (around 32:40.) Not very bright, but still somewhat useful for illumination.

A kerosene lamp probably converts ~2-3% of its energy into the light; I don't think they use catalytic burners.

Dynamos and LEDs are reasonably efficient in comparison, and also not fire-prone.

Here's what people said about it 3 years ago: https://news.ycombinator.com/item?id=4889266

Very interesting to see how they have improved the design since then with development of the GL-02:


A more efficient LED, a power output port, and continuous operation, but most notably: a pulley system! Great how a simple machine can massively improve the impact of this product. Very cool.

It's amazing the amount of people who immediately cry hoax. Someone raised a good point about taking money from locals and bringing it to Europe/America/China, but clearly this isn't breaking the law of physics.

The original OLPC attempted to ship a pull-cord generator. Trevor Bayliss, of Freeplay radio fame, proposed a generator based on hoisting a weight on a branch of a tree. The principle is sound. As for taking money from locals, I would be surprised if kerosene was produced locally... and even if it was, this is a one-time expense, versus an ongoing outlay.

I worked at OLPC. We didn't ship any kinetic charging systems as the most reliable ones had a mean time to failure on the order of ~three full charges. The scheme was cute and captured the imagination of people in the developed west but is fundamentally unsound due to the cost of high precision, reliable manual chargers and their miniscule power output. In addition to yielding only several full charges before the $50 charging unit failed, each charge would require tens of thousands of revolutions of a hand crank. As wonderful as the laptop was I think it would be a very strange thing for a child to do when they could easily play with something more immediate.

In practice most of the laptops are charged like other laptops--- from national power grids. Those that aren't are charged from diesel generators and solar power.

It's gratifying to see how much more substantive and less dismissive this thread is than that one from 2012. Partly it may be that the project itself has developed, but I'd like to think that HN threads have improved too.

The previous thread was linked to a crowdfunding campaign, which this may have influenced the conversation substantially.

Its cool our energy problems are being solved in two directions at once. We are (slowly) making better energy storage and generation devices. At the same time many of our energy needs go down by the rapid decrease in energy needed to power the electronics. It would be cool to see a graph of the watts/lumen efficiency of light bulbs over the last 50 years and of the joules/operation of CPUs.

Manhour/lumen is the only measure I know of that captures all of the elements of economic growth and can be estimated for every culture and back to before the development of spoken language.

Nitpick, I know, but: it's not powered by gravity it's powered by human muscles, so in the end - by food.

If we're playing that game:

- Human muscles get energy from food.

- Food is or gets its energy from plants.

- Plants get energy from the Sun.

- The Sun's energy comes from gravity-forced fusion.

So gravity :)

Stars are the original GravityLight.

Good point, but it's not the end. Fusion uses up energy put there by the Big Bang :)

The Big Bang came from....gravity?

Is this the science consensus? I thought it's one of competing unconfirmed theories?

i believe it is very much the consensus.

the FLRW model of cosmology, which has made numerous confirmed predictions teaches us that the big bang is a geometric property of space-time i.e. a consequence gravity, and particularly Einstein's field equation from general relativity.

So by your logic fossil fuel is solar energy.

It is, it's just massively time-shifted.

It's interesting to put that in perspective: the pyramids were built out of solar energy by way of muscle. Skyscrapers are built out of solar energy mostly by way of diesel fuel.

Fossil fuel is a solar battery; charged in a couple hundred million years, humans will drain it in ~500.

No wonder we're seeing exponential growth with that injection of stored energy into society. The industrial revolution is a coal-powered nitro.

Checkout this explanation of fire by Richard Feynman - its a really eye opening perspective


He explains the light of a fire is just the light of the Sun, it's just been stored in the wood

By causality, it kinda is.

It is. Except for geothermal energy brought on by radioactive decay, all energy on earth originally comes from the sun. Fossil fuel is sunlight that was absorbed by plants which then either decomposed into fuel over millions of years, or were eaten by animals which later decomposed into fuel over millions of years. Our cars are powered by very old, stored sunlight.

And radioactive elements come from long dead suns, so all energy on earth originally comes from A sun.

You are now qualified to take a job as an oil company or nuclear energy lobbyist.

I don't think it's a nitpick. I think this is a very important point. Is the hypothetical fuel more expensive than food?

I think your muscles are pretty energy efficient.

The kinetic potential battery (the weight lifted against gravity) is also very efficient.

Food is very energy dense. https://what-if.xkcd.com/128/ (sandwich vs battery)

Uh, change of topic: isn't the caloric value of a food how much heat can be released by burning it (probably when it is dehydrated)? Plenty of energy stored in a sandwich, sure. But a car battery could power a small spaceheater-like thing for... a while. There's a lot of potential for heat production in a car battery (even without BURNING it). Did Mr. Munroe get this one wrong?

From Wikipedia: https://en.wikipedia.org/wiki/Muscle#Efficiency

> The efficiency of human muscle has been measured (in the context of rowing and cycling) at 18% to 26%. The efficiency is defined as the ratio of mechanical work output to the total metabolic cost, as can be calculated from oxygen consumption.

LED is much more efficient than kerosene lamp, so I guess yes.

I take your point, but the food ultimately gets its energy from the sun, which gets its energy from collapsing under gravity. I don't think there's a clear place to stop, but I'd say the name Gravity Light gets the idea across anyhow

Sun is powered by fusion. Gravity just holds it together.

The fusion persists because gravity forces hydrogen sufficiently close together.

So gravity is a catalyst, not the energy source.

its a symbiotic relationship. stars exist generally at an equilibrium point where gravity is trying to make it collapse, but the pressure produced from the constituents pushing outwards balances it out.

this is because if something is collapsing from gravity it will stop once some other force is pushing out harder.

this explains a lot of phenomena and is a key piece of understanding the modern theories of stellar phenomena, e.g. via the pauli exclusion principle, why neutron stars can form during a supernova (from the extra inward pressure combining with the gravitational collapse exceeding the degeneracy pressure of electrons in the plasma)... its also why beyond a critical mass the collapse doesn't stop at all and produces a black hole.

in any case energy is always conserved... but the ultimate place it is being extracted from to power a star is the gravitational field. everything else, e.g. the nuclear fusion, the light pressure from temperature etc. is a result of that energy being transferred into the star as it forms and continues to evolve.

By that logic my car is powered by steel, because that's what keeps the fuel-air mixture sufficiently close together.

Close, but not quite. The steel of your engine did not cause your engine to exist. But gravitational collapse of interstellar gas is the process that formed the sun. So, in that sense, gravity comes before the fusion.

It's common to say a car is powered by fuel. It's also common to say a car is powered by its engine. The latter is indeed is a device that brings fuel and air close together (and does some more important things). It's less common, but certainly not wrong, to say a car is powered by combustion.

Similarly, I think saying both 'the sun is powered by gravity', 'the sun is powered by hydrogen' and 'the sun is powered by fusion' is reasonable.

The basic idea here is actually a very old approach -- clocks have been powered this way for centuries. But it's very cool and refreshing to see a modern electrical spin on it.

Might be fun to make an electric clock that uses gravity, go full circle.

Rotor systems like in some automatic watches produce very little energy. Even at 100% efficiency it wouldn't be able to sustain an electronic circuit.

Edit: I was wrong. See below.

Seiko Kinetic watches are quartz watches that are powered by movement. That's 30 year old technology.

I stand corrected

Not only is that not what I was thinking of, which was more akin to a grandfather clock, but I don't believe that at all. Just using piezoelectric vibration sensors I was able to charge a cap to light up an LED- a rotor mechanism would generate much, much more power, and consider today's energy efficient ICs I see know reason why it wouldn't work.

My automatic watch contains an electronic circuit, so I'm not sure what your point is.

Interesting. What is the circuit for ?

Are you sure it's not powered by a standard watch battery ?

Yes, it is a quartz movement with a capacitor that is charged by a mechanism similar to a mechanical auto-winding watch.


It would be great if the gravity system was bidirectional, so that you could just flip it upside down instead of lifting the weight each time.

Perhaps a bit of a novelty given the rechargeable battery argument others have mentioned. I imagine distributing a bunch of these with batteries and having a central dynamo-powered recharging station that gets shared throughout a community would be even more practical.

The first thing that came to mind when I saw that it lasts 20 minutes would be to use it as a pomodoro timer. Code for 20 minutes, then be forced to take a break, stand up, lift the weight, etc. You get a micro-workout as a small bonus. Again, it's a novelty but sort of a cool one at that.

I was rather hoping this would be a hawking radiation method, i.e. actually generating light using gravity

You and I both. This isn't even carbon neutral. I mean technically this is burning carbon molecules.

burning carbon molecules sourced from photosynthesis. Carbon positive, but the fuel generation is carbon negative, so it balances out.

Loads of great social tech ideas including this one on Social Tech Guide (http://socialtech.org.uk/), nominations are open for new ones at the moment if you come across any more..

Why downvote this? Seems legit.

A 12kg weight hanging 6 feet in the air seems a little dangerous to me. Definitely less dangerous than a kerosene lamp, but I'd be worried about poorly attached weights falling if someone bumps their head on it.

Do you own a TV? It's certainly way more dangerous than that.

This is wonderful. I plan to buy at least one for emergencies, and also to help make them cheaper for others.

A battery powered LED torch is far superior for emergencies. The only reason you'd really want to use this is if you really can't afford a solar-rechargable battery. (But for some reason can afford this, which I'd expect to be more expensive.)

Although that might be true, battery powered flashlights/torches suffer from the problem of leaky batteries. I've tried to use many flashlights that don't work, only to find the batteries have started to leak acid and ruined the flashlight. Sure, one should check the batteries every year or so, but who really does that? I'm not saying the gravitylight is a good replacement, just that battery powered flashlights do have some drawbacks.

This is what lithium primaries are for; they don't leak.

And before anyone jumps in and says "lithium batteries self discharge!" Yes, yes they do. But it's really, really small. It discharges quickly initially, but then tapers off to about 1% per month.

> A battery powered LED torch is far superior for emergencies. The only reason you'd really want to use this is if you really can't afford a solar-rechargable battery.

Rechargeable batteries can be reused, but still need to be replaced; this may prove lower maintenance, which means once you can get it, you are more secure with it with a less secure distribution system. In many of the places where people are without electricity in the world, that's potentially a significant benefit.

(Also, solar recharging in places that experience long periods of darkness, e.g., the arctic, may not be an ideal solution. There aren't any places that experience extended periods without gravity, at least not on Earth.)

That's true, but the statement was as to its usefulness in emergencies. This thing is fixed to the wall, limiting what you can use it for in an emergency. For example, if you have to find your car keys in a different room, make emergency repairs to your water mains after an earthquake, or figure out how to get a friend out from a collapsed wall in the dark, a torch is more useful.

For emergencies, I would prefer a mechanically powered flashlight with a supercapacitor over this thing.

12kg * 10 m/s^2 * 1 m = 120j. Best 100 w equivalent led is 18 watts, 120j/18w < 10s. Let's say optimistically a next gen led gets 10x efficiency (this might violate laws of physics), you're buying one minute of good light per 1 m lift.

For those interested on exactly how to set one up and how it works, there is a great Vimeo video outlining installation and operation:


what is the deep difference between this mechanism and a simple spring / coil?

Precisely the same question I have as well. Especially given that the energy you could store in a spring or coil could be much more, and you are not limited by one's lifting capacity or maximum height. Anyone have an idea?

You need to lift a 10KG weight about 2 kilometres to get a teaspoon of kerosene's energy, so it's not a great replacement on that front, and having 10KG weights dangling around at variable points between ceiling and floor sounds if anything even more of a liability than a lamp with a naked flame, which does at least stay where its put. Sorry to be negative but it's difficult to conceive of a realistic scenario where decent battery plus solar doesn't knock this into a cocked hat.

> You need to lift a 10KG weight about 2 kilometres to get a teaspoon of kerosene's energy, so it's not a great replacement on that front

This says nothing of light output. If you want light, and most of kerosene's output is heat, your energy calculation is not helpful.

> and having 10KG weights dangling around at variable points between ceiling and floor sounds if anything even more of a liability than a lamp with a naked flame

This seems like an incredibly contrived "problem". What's the liability? Somebody may bump into a somewhat heavy object that is moving downwards at a barely perceptible clip? Somebody may tweak their back lifting the weight? That seems lower risk than my housing burning down with me in it.

Okay, okay, you are right of course, the light efficiency is very different, although the heat may not be an altogether unwanted by-product in many cases. There are also more efficient ways of getting light from petroleum than sticking a wick in it. But if you do want the benefits of LEDs, there are better ways of getting the energy than lifting sacks to the ceiling. It's still 180 meters for a pair of AA rechargeables.

I genuinely don't think the hazards are at all contrived, and range from the grave if unlikely to the mild but virtually certain. You are surely going to knock your head on this massive hovering, albeit reasonably well lit, object on a regular basis, and it might not be as soft and rounded as the illustration. On the floor, in dark mode, you'll be tripping over it, which doesn't always end comically. Reasonable precautions not withstanding it's not impossible that it could crush or smother something beneath it even at its snail's pace, but more likely it could come down hard through overloading, wear or misuse. It's really not something I'd want in a family home.

It is a nice idea and obviously of the very best intentions but I'm afraid it's simply misguided and efforts would be far better directed towards battery plus solar. Sorry.

I would say the hazards of this device sure beat the hazards of kerosene lamps (fire, mostly). [1] lists a series of accidents with kerosene lamps in a three year period in a small town. I think a horse kicking over a kerosene lantern started one of the big Chicago fires. There's even a possibility that a kerosene lamp caused a deadly fire in modern USA [2]. And I'm guessing that fire would be a serious problem in small, dense areas such as the slums (not intended pejoratively) in the third world nations that are likely to have the most use for this.

Solar plus battery might be better than this, but this looks like a whole lot better than a kerosene lamp.

[1] http://www.thelampworks.com/lw_lamp_accidents.htm

[2] http://www.chicoer.com/20120322/kerosene-lamp-may-have-cause...

The amount of energy is not directly comparable if the efficiency of its use is very different. A kerosene lamp is multiple orders of magnitude less efficient than decent LEDs, so while you might have to lift 2KM to get the same energy, you'd have to lift much, much less to get the same amount of lumen-hours.

A kerosene lamp has an efficiency of 0.1-1 lumens/watt, while a white LED has anything around 80-100 lumens/watt.

> weights dangling around at variable points between ceiling and floor sounds if anything even more of a liability than a lamp with a naked flame, which does at least stay where its put.

Fire stays where it's put? No. The problems with flames involve toxic gasses poisoning people and the occasional building on fire. That's really not consistent with the idea that "flame stays where its put"

Can't you suspend a bed wired to one of these to the ceiling? At night before you go to sleep climb the stairs and get into the potential energy elevated bed. Then in the morning, after the bed descends, you have enough reading light energy stored for the next night.

How do you lift the suspended bed back up again?

Unhook the four corners from the system, raise the "hooks" and have 3 or 4 associates help you lift the bed on to the hooks?

It seems unlikely 3 or more people would like to lift a heavy bed each day. It could work in principle, but I do not think it is comfortable enough.

Regarding the energy of lifting a 10KG weight 2 KM high is not a 1:1 comparison with the tech here. It's using an LED which much more efficient than a Kerosene powered flame, since most of the energy in the flame is spent in infrared.

How much of that energy of the kerosene is converted to visible light?

This is some LEDs, a weight, some gears and an alternator. Is a solar panel and a battery going to come anywhere close in price?

downvoted hard for assuming that most of the energy consumption by kerosene goes to visible light, LOL, come on man

It looks quite a bit more plausible than the specs in http://www.howtospotapsychopath.com/2008/03/03/stop-press-pi... , but based on my experience with things like shake/crank torches, the light output would have to be really low to last as long as they claim it does.

these look interesting... but like all things like this i wonder what the actual costs are of lifting the weight is?

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