GravityLight is a gravity-powered lamp designed by the company Deciwatt for use in developing or third-world nations, as a replacement for kerosene lamps. It uses a bag filled with rocks or earth, attached to a cord, which slowly descends similar to the weight drive in a cuckoo clock. This action powers the light for up to twenty minutes.GravityLight is a gravity-powered lamp designed by the company Deciwatt for use in developing or third-world nations, as a replacement for kerosene lamps. It uses a bag filled with rocks or earth, attached to a cord, which slowly descends similar to the weight drive in a cuckoo clock. This action powers the light for up to twenty minutes.
An early GravityLight concept was developed concurrently by Clay Moulton and also by Mike Wofsey as part of his Ph.D. in applied physics from the University of Alabama in 2006. While Moulton did not reportedly develop a prototype, Wofsey did develop a rudimentary prototype that used a custom-machined rare earth magnet motor with minimal gearing. Wofsey secured the www.gravitylight.com domain to disseminate the findings, however he did not pursue the gravity light as he decided the efficiency was too low to be commercially viable. The theoretical efficiency of the device is limited by taking the simple potential energy generated by raising a mass to a specified height, and then dividing it by the desired time that the lamp is to stay lit. Even a relatively large mass of 10 kg, when raised to a height of 1 meter, produces a maximum available energy of only about 98 joules; dividing by a desired illumination time of just 5 minutes would return a usable power of only 0.32 watts. Moreover, this would be for an unrealistic 100% conversion efficiency; that of the University of Alabama prototype was closer to 50%, which in our example would further reduce usable power to just 0.16 watts. At 5.5 operating voltage of an LED, that left only 20 milliamperes for the LED. This is sufficient to light an LED, but the available light from the LED would not likely be useful for reading or night activities. A modification to this approach was suggested where the power draw can be adjusted by the user to trade illumination brightness for illumination time.
The first IndieGoGo campaign of GravityLight was ended on January 18, 2013 with $399,590 funded by 6219 funders.
The second IndieGoGo campaign, GravityLight 2: Made in Africa ended on July 18, 2015. It featured an improved design and the goal of manufacturing them in Kenya.
Martin Riddiford and Jim Reeves worked on GravityLight as a side project for four years.
There are no operating costs after the initial purchase of the appliance. A standard GravityLight kit comes with an adjustable lamp and a ballast bag. The light can be turned on by filling the bag with approximately 20 pounds weight (10 kg) and lifting it up to the base of the device; the weight falls over a period of 25 minutes, pulling a cord/strap that spins gears and drives an electric generator, which continuously powers an LED. This creates enough energy to last 25 minutes whenever it is needed.
The second model, GL02, also includes two SatLights and connecting cables. These are separate lights that are wired in series from the main GravityLight unit. Each SatLight can be turned on or off separately. When used with SatLights, the light on the main unit can be turned on or off. Up to 4 SatLights can be connected, giving extra light to different locations in the house. The rate of the bag drop is almost not affected by the number of SatLights attached.
The original GravityLight used a strap for pulling up the weight. The improved GL02 used a plastic-bead chain on a pulley system. The pulley system requires less strength to pull up.
GravityLight was called one of The 25 Best Inventions of the Year 2013 by Time Magazine.