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A $5 Lamp Powered Solely by Gravity (enpundit.com)
253 points by TannerLD on Dec 21, 2012 | hide | past | web | favorite | 88 comments

Previously submitted and seriously doubted:


In that thread[0] revelation[1] said:

    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.
[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...

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.

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"

It's hurts to look at it because it's focused into a very narrow beam. Very bright sure - in one tiny spot, and totally useless to illuminate a room.

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.)

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.

That's assuming a perfectly efficient dynamo and no mechanical losses. (Which are both huge assumptions.)

Exactly, and since they state that they think they can make it twice as efficient, that would mean they run at max 50% now.

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.

Using the numbers above and the typical LED efficiency you get 5 lumen of light per half hour ASSUMING perfect mechanical efficiency.


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.

But you can adjust the ballast weight and the height; instead of 20 kg over 1 meter, how about 30 kg over 2 meters? That's a factor of 3 difference.

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.

How many people can lift 30kg 2 meters up?

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?

Why are you limiting your scenario to only one of these lights?

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.

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.

A pedal generator would probably cost more than $5, though.

Not to mention the supercapacitor.

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.

well here's the agency behind it... pretty elaborate if it is a hoax: http://www.therefore.co.uk/our-work

Not to nitpick, bit it's not powered by gravity, it is powered by people going over every 30 minutes and lifting a weight back up to its top position.

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.

People couldn't lift the weight without consuming energy from food. Doesn't mean that it's powered by food.

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.

> People couldn't lift the weight without consuming energy from food. Doesn't mean that it's powered by food.

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.

Food gets its energy from the Sun, so we may as well just call this device solar powered?

Ad bigbangeum.

I suppose it all ultimately comes from solar energy, which, in turn, comes from nuclear fusion.

And the nuclear fusion is started if not powered by the heat and pressure caused by, wait for it...


Which is induced by the intense pressure gravity creates in large lumps of mass :) so yeah..

That is not entirely true. Nuclear fission is not powered by the sun, nor are nuclear fusion plants on Earth (when they arrive). However, fission is only possible because of the existence of heavy nuclei that were initially created during super novae explosions in massive stars billions of years ago so you could argue that is is also at least star powered.

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.

When I think "powered solely by gravity" I think of something like a hydro electric plant which can generate more energy than is required to operate it.

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:


Gravity is the storage mechanism. When someone says something is battery-powered, do you start an argument about how that technically isn't correct?

Probably yes. Annoying pendants are predictably annoying.

I think you mean "pedants". ;-)

Perhaps he was talking about a particularly obnoxious piece of jewelry.

Gravity isn't the storage mechanism; the ballast bag is. Gravity is the mechanism used to unleash the stored energy, the same way that the electro-chemical voltage difference between the two components of the battery is the mechanism that unleashes the stored energy in the battery. If anything, it's a ballast-bag-powered light.

I'd say you have the most accurate description of when they say "Gravity Powered". While lifting this thing, the energy gets stored and gravity is just a means by which the stored energy is released.

I was a bit disappointed by the title. I was hoping for something akin to a sterling engine, which is powered solely by a heat differential. As long as the heat differential is present and barring any mechanical issues, the sterling engine will operate continuously without intervention.

If you bury a heatsink, and then have an air-flow heatsink, it's plausible that you could power a Stirling Engine with this kind of power output.

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.

They're incredibly efficient. There's one on my wireless router that happily spins away all day.

Technically, really technically, and very pedantically, I expect what you have is a hot air engine, because it's unlikely that it includes a proper regenerator, which is technically what differentiates a Stirling Engine.


Yes, Stirling Engines can be wonderfully efficient, and they are a delight to watch in action. Lovely machines.

I'm pretty confident that most comments that start with "not to nitpick" would be better sent to /dev/null. Nitpicking is usually a sign that deeper, more interesting arguments aren't available, but negativity must reign supreme!

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.)

Some people get excited by F1 racing, the Bugatti Veyron, or stuff like the latest iPhone, telling you they are technology enthusiasts or engineering fans.

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.

> it's always at the low end of things - like this project - where the really inventive, exciting engineering happening.

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.

You're just paying attention to different constraints. Engineering with zero constraints is pointless- but an F1 car operates within all kinds of constraints that are not money. You just aren't familiar with them.

You might think it is "truly spectacular" because it is unique to you. But you have to question yourself if it is really THAT effective. One could buy a hand cranked powered led light for cheaper. Sure, it'll take more time to power it. (Few seconds vs a minute). If i could afford neither i would go for the second option.

"To define it rudely but not inaptly, engineering is the art of doing that well with one dollar which any bungler can do with two after a fashion." -- Arthur M. Wellington

My favorite way of expressing the same thing: "Anyone can design a bridge that will stand up. It takes an engineer to design a bridge that will barely stand up."

Not sure where this came from -- Douglas Adams, maybe?

indeed! having lived in india, i get particularly excited by projects that could provide grid-free lighting and clean water to rural areas.

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.

> i get particularly excited by projects that could provide grid-free lighting and clean water to rural areas.

The best way to provide lighting and clean water is via the grid: power lines and water pipes.

yes, in the long term i agree, but extending the grid's reach and capacity happens slowly, and in the mean time the poor lead miserable lives. these low-tech stopgap measures are things they can do now to improve their lot, for little up-front cost (in business terms, the grid has lower opex, but way higher capex)

Maybe I'm stupid for asking but what is the advantage of this over a spring powered wound clock? My wristwatch can tick for two days on a wind, and while it isn't as cheap as this gravity powered wound clock I'm sure it could be made cheaper. There is nothing special about this invention; purely mechanical "gravity powered" clocks have existed for centuries in the form of old grandfather clocks etc.

The advantage of this lamp over a spring powered wound clock would be that it emits light. The disadvantage is that it's comparatively poor at keeping the time.

True, but my question is if a clock winding mechanism can keep going for days without need of winding could a clock winding style mechanism be more efficient than a gravity weight powered one.

SCNR. I suppose the advantage of clock winding mechanisms is that they can deliver (mechanically) a constant, relatively low level of power. Compared to an LED, a wristwatch uses very little power (about 1µW according to Wikipedia). Of course this lamp may be more comparable to a grandfather clock than a wristwatch; I don't know how much power a grandfather watch requires, but the energy you store winding it up can't be that high since it's not that much work, and the strength of the mechanism is that the stored energy is then delivered over a long time, ie. days.

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.

Yes, I was thinking the same thing. You can buy now on Amazon a hand-crank LED light for $12, so surely these can be made far more efficient and cheaper with $200,000.

But those require a battery, which will only survive so many (hundred?) recharges, no?

I think they use capacitors. At any rate, almost anything would be better than "gravity power". Even a flywheel.

I'm not sure why you think flywheels would be a better energy store than a bag of rocks.

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 use kerosene lights by choice in the winter in weeks like this one when there is no sunshine. So, here's my firstish world problems take on it. May not apply to people for whom a gallon of kerosine is a significant fraction of their monthly income.

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.

>a gallon of kerosine is a significant fraction of their monthly income

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.


This idea just hit me, and it's so powerful I'm still reeling. What if someone built a battery-powered weight lifter that would go off every 1/2 hour? You wouldn't have to keep getting up to do it yourself!

Not sure if I should patent this, or just donate it to the greater good of mankind.

are you proposing propetual motion? if you have the energy to lift the mass, you have the energy to power the light directly and bypass the losses of setting up the dravity weight again.

First thing I thought when I saw the title was: Linux, apache, mysql, php...

I'm not sure why you were downvoted, as I bypassed the article probably at least a couple times before realizing that it didn't say "Lamp Server" and just said "Lamp".

"A $5 LAMP Server Powered Solely by Gravity", if I read that I would have clicked instantly.

Technically powered by the effort of lifting it.

Technically powered by the food eaten to lift it.

Technically powered by the sun.

Technically shut up with useless pedanticism.

I don't think that's useless pedanticism at all. If you didn't know anything about physics, you're likely to hear "powered by gravity" and think "great, gravity is ubiquitous and free, so this is totally free energy", whereas actually these poor people will have to eat more in order to light their homes. So it's important to communicate what you actually have to do to power this light.

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 not very useless. The title suggests a perpetual motion machine, so I was wondering what that was doing on HN. Knowing you have to lift it first (from the article or from the comments) is important to know and lets one think this isn't necessarily made up.

You infer a perpetual motion machine, they say it is 'powered by gravity'.

Which is something I infered as well, and probably many others. The title is confusing and that is all the OP was pointing at, so you know, be nice - he wasn't trying to undermine the achievements, if any.

If you had an infinitely long rope and access to an infinitely deep chasm, then there's no reason it wouldn't be considered a perpetual motion machine.

With an infinitely long rope and an infinitely deep chasm there would not be substantial gravity pulling it downward to have perpetual motion.

No gravity would simply approach infinity as you descended the well. And since we're being pedantic that's not an issue.

Similar in concept to the Waka Waka light, except that's powered by a solar panel (and some quite nifty electronics):


As always, the devil is in the details here. Does this lamp produce enough light for a family to be motivated to actually lift it every N minutes (e.g. does it produce enough light to read comfortably, or to cook a meal)? Is it durable enough to survive in essentially outdoors conditions in terms of heat and humidity? If the answers to these questions are positive, it's certainly a great invention. If not, back to the drawing board.

As we all argue over whether this is powered by gravity, or food, or nuclear fusion, somewhere in a dark hut someone is lifting a weight to attend to the baby that just woke up in the middle of the night.

This is not a new idea. Cuckoo clocks, which is common in germany, works without a battery. we need to pull up the weights everyday.

I don't seem to be in the target audience but the first question that came up is: How much noise does it make?

I don't quite understand HOW does it turn the weight into energy. Could someone enlighten me?

the weight is on a string. That string is connected to a crank that turns a generator as it falls.

Oh, and as I understand, the amount of weight is important due the resistance of the crank?

It's not powered 'solely by gravity'

It's powered by a human lifting the weight.

If it's real, I wonder if the gears are noisy...

Pretty cool idea.

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