It's a playful name for a serious company: D.light Design sells $10-to-$25 solar-powered lamps in more than a dozen countries where people lack electricity and often spend a lot on kerosene, which gives off noxious fumes. D.light's latest model also recharges phone batteries. But one of CEO Sam Goldman's goals is to find ways to lower the cost even further. "I'm not satisfied with $10," he says. "The real customers that we started this business for can't afford that."