Gravity has videos on technology and business. We learned about “GravityLight.” It works like an old grandfather clock: A smallbox is connected to a weight. As the weight drops, it runs a series of gears which spins an electric generator. It never needs sunshine or batteries and can light a 100-watt bulb. Every 15-30 minutes you have to lift the weight up again to keep it going. It goes on sale later this year. Cost is expected to be around $7.

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