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Inventors Design Lamp Powered Entirely By Gravity


This is SCIENCE FRIDAY. I'm Flora Lichtman, filling in for Ira Flatow today. Solar, wind, geothermal - now there's a new renewable energy source to add to that list. It's free, completely reliable and totally unlimited: the force of gravity. Two British designers have invented a lamp that runs on gravity alone. Their GravityLight - yes, that's its name, aptly named - uses, you guessed it, the pull of gravity on a weight to generate up to 30 minutes of light.

To turn the lamp on, you lift a weighted bag up, and voila, as the bag slowly descends, LED illumination. So how does this work? How hard is it to make? My next guest is here to tell us. Martin Riddiford is one of the inventors of the GravityLight and founder of the design company Therefore. He joins me by phone from London, England. Welcome to the program.


LICHTMAN: Hi. Tell us what this GravityLight looks like, and then take us under the hood and tell us how it works.

RIDDIFORD: OK. So GravityLight is a project which we started because we were working with a charity trying to find an alternative to kerosene lamps for the developing world. And we were working with solar power at the time, and we were doing a lamp which used LED bulbs and a battery. And we - you had to charge it through solar panels. And we found out that the cost of the unit was too expensive for people in Africa to buy, because they have very, very limited finances. And there's no micro-financing in Africa.

So the lowest possible BOM cost, or purchase cost, was absolutely essential in the project. So we came out of a meeting when we presented our - the latest work we'd done with the battery-powered device, and thought, we've got to find a cheaper way of doing this.

LICHTMAN: Now, how did you come up with the idea of - how did gravity come to mind?

RIDDIFORD: Well, we realized that there were two components, the LED and the battery, and, obviously, the means of charging it. And - but there are various means of charging devices like this, with hand cranks and things like that. But they generally always involve a battery, and we were trying to think of a way of getting rid of the battery. And this is where the gravity side came in.

So we envisaged this scenario where you lift the weights, as you say, the heaviest weight you can lift, about 10 kilograms or 20 pounds, as high as you can lift it, about six foot. And then you let it go, and this device releases the bag very slowly and powers a generator to create a very small amount of electricity, but enough electricity to give you sufficient light - well, more light than a kerosene lamp would give you.

LICHTMAN: So no battery required. It's just a teeny, tiny generator.

RIDDIFORD: Exactly. And that's one of the interesting things, because not only is it - can it create light, obviously, but because it's a generator, we can potentially charge batteries and things like that. But in a very - very, very slowly, which is important to realize. This isn't a way of generating large amounts of electricity, but because the developments of LEDs and electronics make power consumption less and less over time, then this kind of project becomes more and more worthwhile, because we can do more and more with the small amount of power that we create.

LICHTMAN: And how much power are you creating?

RIDDIFORD: Well, we call the project Deciwatt, which basically tells you how much power it's creating. So depending...

LICHTMAN: So a tenth of a watt then, is that right? Just for people...

RIDDIFORD: A tenth of a watt, yes. So depending on how fast you let the weight travel down depends on how much light - how much - sorry, how much energy you get out of it. So the prototypes that we built generate between 30 milliwatts and half a watt. And we've got a variable drive on the end, which allows us to change from the very low power condition, where we're just able to light an LED and use it as a nightlight kind of thing. And then we can, as I say, generate half a watt for more of the sort of battery charging things that we're experimenting with.

LICHTMAN: Well, I guess our bright light - it's like a built-in dimmer.

RIDDIFORD: Sort of thing, yeah. They - one of the things that we discovered fairly early on was that the whole rig is a bit counterintuitive. So if you were imagining that you were going to increase the heat on a fire, you would chuck another log on, and you'd expect the log to last longer and also to give you more heat. The trouble with the GravityLight is that you - if you put more weight on it, it descends faster, so it lasts less time. But it doesn't necessarily light the LED much lighter because it's all about the efficiency curve of the LED.

LICHTMAN: Ah. So it's hard to scale up. You're not going to run a toaster off of this if you have a really heavy light, necessarily.

RIDDIFORD: No. It's really suited at this kind of deciwatt range. I mean, lots of people have said, oh, yeah, you know, I want to hang it from my, you know, third story. But the other part of what we're trying to do here, which is what makes it interesting, is that other systems - like a hand-cranked torch, or whatever - requires the user to invest quite a lot of time in doing the rewinding. So the joy of this system is that one very swift operation, three seconds or so, gives you 30 minutes of light. So there's a big payback for a very short period.

LICHTMAN: How much does it cost to make?

RIDDIFORD: Well, currently, the costings for the first prototype at about 5,000 units is about $6.50. But we've got various - a couple of bearings in there that we hope to not need in the future. And we, you know, we're obviously not using much buying power in terms of buying the LED and the motor. So what we're trying to do is to trial a thousand of these units in Africa and get all the feedback we can from how people use them, how high they hang them, how much light they need. Do they have it turned to the dimmest or the brightest? What else do they want to do with it?

We put a couple of terminals on the outside as a sort of open-source hacking kind of facility, so that you can attach other things to it. So you can attach, for instance, a radio to it and run a radio perfectly satisfactorily from it. You can attach a task light from it and use it for, sort of, desk reading. And as I say, you can charge batteries from it. So part of the trial that we're planning on doing in the next six months, we're going to build some of these accessories and give them to people and find out how they use them and how they get on.

LICHTMAN: You know, I know this isn't meant as a way to replace kerosene lamps, but I can imagine a market here where electricity is available, too. Have you ever thought of doing something like the TOMS model, the TOMS Shoes, where you buy one and they donate a pair, as well?

RIDDIFORD: Well, interestingly, we've been developing this for a number of years as a sort of skunkworks project after we did this project with our charity. And we got to a point where we've got these prototypes working, and we want to tool up and make enough units to go and distribute around the world to get the feedback that we need.

And we decided to use a crowdfunding campaign to do that, and we had terrific success there. Over a period of a month or so, we've raised hundreds of thousands of dollars, which enables us to pay for the tooling, but also to do research and other things with it.

But the other side of crowdfunding, which is wonderful, is that we've connected with a whole bunch of people around the world - firstly, a whole bunch of really generous Americans. American people probably account for 50 percent of the funders for our enterprise. And then we've connected with a whole bunch of people in developing countries who are wanting to distribute or help us do this research, or they're charities, or whatever.

So we've got a really good spread of contacts through this, and a number of the American people who've funded us have said, well, you know, we live in Canada or northern America and we've got - you know, we do a lot of outdoor stuff. We'd love one of these, you know, for camping or in our hut or whatever in the wilderness.

So we're going to send a whole bunch of units out to people and see what happens. Sorry, the crowdfunding thing that I was talking about, we did a buy one for yourself, and then gift one to - for this trial. So - and that's the way that we would probably sell it in the West, is to do exactly that kind of thing, which I think people buy into very well.

LICHTMAN: Is your design company working on any other gravity-power applications?

RIDDIFORD: Well, we're currently - because now we've got the funding to do it, we're exploring lots of other opportunities. And we've got this internal development group who are currently looking at where those opportunities might take us. And we have sort of an ambition that we could potentially have a battery-less system for getting on the Internet, but it's obviously a long shot. And we need to do the research to find out whether we can do that within the power budget that we have.

But the notion is that we could - one of our clients is Inmarsat, who do stationary satellites. And we want to try and engage with them to see whether we can do a receiver for broadcast satellite information which runs at this kind of very low level. And if we can, then it would be great to imagine that we could, say, download a Wikipedia page with a device without batteries.

So that's a long-term goal, which may or may not be achievable, but it's - you know, we're setting our sights high.


LICHTMAN: Absolutely. It's exciting to think about. Well, good luck to you.

RIDDIFORD: OK. Well, thank you very much.

LICHTMAN: Thank you for coming on. Martin Riddiford is the founder of the design company Therefore and one of the inventors of the GravityLight. Stay with us, because our next segment is something that I think is on the minds of many people this season. It's the flu virus. We're talking about its preferred habitat, how it travels, and how to stay - how to outsmart it. Stay with us.


LICHTMAN: This is SCIENCE FRIDAY, from NPR. Transcript provided by NPR, Copyright NPR.