Riddiford knew a falling weight could produce enough energy to run a grandfather clock, so why not a light? To find out, he attached the crank of a wind-up flashlight to a bicycle wheel. He hung a weight from the wheel to cause it to spin; the wheel cranked the flashlight, and the device lit up.
Over the next four years, Riddiford, Reeves, and a small team spent their downtime between projects in a basement, refining the GravityLight. To use it, a person hangs the device and fills an attached fabric bag with up to 28 pounds of rocks, dirt, or other material. Lifting and releasing the bag steadily pulls a notched belt through GravityLight’s plastic hub; the belt spins a series of gears to drive a small motor, which continuously powers an LED for about 30 minutes.
The team used crowdfunding to manufacture 1,000 GravityLights, which it plans to send to developing countries for field testing—plus 6,000 more for backers. “It’s exciting to witness so much positive reaction to what we’re doing,” Riddiford says. Besides remote villages, the lamp could prove handy in campsites, closets, and any dark nook far from a socket, so Riddiford also hopes to license a retail version for less than $10.