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A $5 Light For The Developing World With An Ingenious Fuel: Gravity

The GravityLight gets power from the slow lowering of a weight. All it takes is enough elbow grease to hoist the bag, and you can light a room with nothing but a bag of sand.

We’ve written about several projects delivering cheap electric light to developing countries. The need is enormous: more than 1 billion people still lack electricity, and many rely on kerosene—which is relatively expensive, highly polluting, and comes with multiple health and fire risks.

Many of the solutions out there are ingeniously solar powered. But GravityLight, an idea from two British designers, is something completely different. It gets its energy from gravity: A 22-pound bag of sand that gradually cranks a gear-train attached to a D.C. motor. One lift is enough for 30 minutes of light, and recharging is as simple as pushing the weight up again.

Martin Riddiford and Jim Reeves are crowdfunding the prototype on Indiegogo, and have already raised almost $100,000. They plan to distribute 1,000 units to villagers during a test stage, before developing and commercializing further. They estimate the current cost at $10 per machine, but reckon they can halve that by scaling up, and finding better materials.

The two initially worked with SolarAid, an NGO that wants to eliminate kerosene lamps in Africa by 2020, because the fuel is expensive and the fumes are bad for people’s health when trapped in a small space. But they soon found that solar has limitations. One, panels and batteries are still relatively costly, especially for durable models. Two, batteries deteriorate over time, and need to be replaced. And three, you have to dispose old units, presenting a potential environmental challenge.

By contrast, GravityLight works inexhaustibly as long as you have the strength to lift it, and provides light whenever you need it. You don’t need the sun to shine, or to store up enough power for evening’s use.

"There is a lot of money going into solar, and it’s being seen as the only way forward," Riddiford says. "What we’re saying is there are lots of places that don’t have enough sunlight to charge panels. If you have two or three dull days, you are running out of light."

The cheapest solar lamps, which include both panel and battery, cost only $5. But Riddiford says you don’t get much for that—he calls the models "toys"—and there are costs attached, such as the price of replacing batteries.

He’s not dismissing solar, though. "Once people have started saving money, after a year or so they might be able to afford a reasonable solar system, if they have enough sunlight," he says.

Riddiford and Reeves don’t claim GravityLight produces a brilliant quality beam—it’s just better than what’s on offer at the moment. "Unfortunately the potential energy isn’t that huge. But it is sufficient light, and it’s free light, for someone who has no other access to electricity."

The illumination is equivalent to a kerosene lamp, he says, but can be supplemented with "task lights" running off the terminals at the bottom of the unit.

"You can do a Christmas tree string of lights extremely well. The strange thing is that you can light 10 LEDs almost as well as one LED. So, you can have general illumination and have task lights," Riddiford says.

It’s nothing like being on the grid. But, as Riddiford says, it’s already better than kerosene. During the testing phase, we’ll find out how it stacks up against solar as well.

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  • Jackson_Johnson

    But lets be honest here.  The two guys are interested in becoming wealthy from the proceeds of this gadget.  Which I think is fantastic and deserved, but lets not pretend to be helping some poor downtrodden group of people who are actually in need of real infrastructure, as a marketing strategy.

    However if your one of those granola crunchers who thinks he's doing to world a favor by purchasing one of these, then by all means, do it.  You will be practicing good capitalism.

  • GraceAdams830

    I am glad to hear that this has come down to $10/unit.  I thought it was about $30/unit.

  • Birchmore

    My ancient hall clock uses the same gravity-power technology. The key to a good light, of course, would be an efficient little geared generator + a good battery to power the motor needed to lift the weight back up every 30 minutes or, if you hung it on a really high skyhook, every few hours.

  • Rob

    These are designed for no-energy living situations (couldn't charge the battery).  If you're assuming the weight were able to charge the battery, what you're describing would be a perpetual motion machine.  In reality, it would require more energy to lift the bag than you'd get back do to energy loss.  It would be more efficient to funnel the energy directly into the light instead of lifting the bag.

  • Rwerthamer

    The energy of a gravitational
    weight as storage for electrical power is full of potential (pun

    Almost any other energy source
    can provide the work of increasing the energy by lifting the weight.

  • marcdepiolenc

    Maybe I'm just stating the obvious, but gravity is NOT the fuel! The fuel is the food eaten by the long-suffering illuminator who cranks the sandbag up every half-hour. Better than nothing, I suppose - I might even like one of these to read by during our numerous power outages.

  • Sima Wieber

    Yeah and so are electric lamps, their powered by the food that the long-suffering illuminator who plugs in the light.  

  • Djika58

    Mwen panse msie gen rezon pase y'ap plede fe yon pil tiplas piblik toupatou yo t a dwe panse ak rout yo.

  • patrick mccarthy

    sad, in my lifetime still no real power plants in "your third world"  -- they should have real infrastructure by now but, no, instead we give them this crap..

    and if you disagree with me, fine.  Please lift your chair over your head every few hours every day in support of this madness...

  • Donald Coughlin

    Our neighborhood experienced a power outage last night around 10PM.  This is the second occurrence within in a
    year.  The last power outage held on for
    five days.  In a major metropolis,
    Olympia, WA, this seems unreasonable.  However,
    this region is fond of older trees right on the thoroughfare.  The power lines take a hit in rough weather.  I imagine the condition will worsen as the
    climate increasingly belches back our CO2 based energy usage. 
    I would like to have one, or better yet two, of these gravity lights for
    home emergency usage.

    I live with only a foot heater at my desk and a two light bulb rule.  LED bulbs or fluorescent are my personal
    choice.  I would like to have the choice
    to replace my lights with such a system. 
    If the opportunity for such a product were available, I really would prefer
    to consider a choice between plastic and aluminum, and other internal
    parts being metal, inclusive of a chain driven bag holder, like the old cuckoo clocks.

    In my opinion, it is perfectly acceptable to charge an American more for
    your product to make a profit and reduce that cost to another who cannot afford
    that cost.  Sign me up for a couple of
    the metal versions with organic cotton weight bags.


  • Mark Connolly Sr.

    It should also be perfectly acceptable to just take money from Americans and just give it away to people who want it. You are so enlightened. Try to think even A LITTLE about what you are saying. Never mind, you don't have to think anymore, you must be tired now. Just saying...Actually, why live like a pig with your TWO light bulb rule and a foot heater at your desk, when people in Africa don't have Any bulbs or even a desk! You should be ashamed! You are such a capitalist pig with your warm feet under your overly lit desk. You should try burning all the crap in your head, that might keep you warm. Go pedal your prius off a cliff into a recycling center.

  • Gabrielgutierrezorcardenas

    me parece bueno acerca de las luces que funcionan con gravedad,

  • Dr. G S Singh

    Its the potential energy which human provide getting converted into kinetic energy and hence light. But the phenomenon is possible due to gravitational pull!

  • David Rice

    "It gets its energy from gravity:"

    Oh good grief. No, it does not get any energy from gravity. Gravity is a static force: it does not contain any energy. The device gets its energy from human muscle, not gravity.

  • Thomas_Hack

    I think you could still accurately say it's "gravity driven" which is just as catchy. Either way, the point is made. Very exciting to consider the possibilities.

  • Leslie Graham

    Pendantic or what.
    I think everyone gets that. It's just a catchy name.

    The most important aspect of this whole venture IMO is that it will enable kids (and adults) to study after the sun has gone down and so learning time does not come at the expense of working time.
    Apparently, in areas where solar lights are being used, literacy rates have climbed sharply.

  • Kkemper1

    a cheap light is a neat idea.  Please consider this additional reponse and comment on it:
    cheap lights is not the need for 3rd world nations.   Access to NORMALLY existing infrastructure
    is what is needed.

    if all those inhabitants would pack up and leave their socialist or Communist homes and move to a true democratic nation, they would have access to cheap, unlimited light.

    The current leaders of your client[s] do not care if they have light.  So, either have them move
    or remove the leaders of these nations.

    YOUR light is a neat idea but is unneeded.  IT's like inventing a cheap car.  Cheap cars
    already exist but if the leadership does not want to have methanol or biodiesel sold in his
    nation, any car will have a hard time.

    I guide my inventors to solve prople's problems in places where the nation's leaders are not
    the problem!  THINK about that.