GravityLight is an LED lamp that, as its name suggests, makes use of gravity to power a light. The lamp is shipped in a fabric bag that the user fills with rocks or sand, connects to the lamp, and lifts. Energy captured from the falling bag powers the lamp for 30 minutes - no operating costs, no batteries required. The designers’ goal is to get the cost of the lamp down below $5 and then deliver the lamps to the developing world, replacing kerosene lamps and bringing light to places that lack public power. Have you seen a similarly elegant solution, something that harnesses available resources, requires just a few inexpensive parts, and is small but has the potential to scale up and have a big impact?