Last year I visited Switch Lighting, a small Silicon Valley company that claimed to have built something revolutionary. Switch’s product: a light bulb that produced the same warm, comforting glow that we associate with Edison’s enduring incandescent bulb but lasts 20 times longer and uses a fraction of the energy. It was beautiful, too. A pear-shaped glass orb that sat atop a shiny metallic heatsink, the Switch bulb looked like a work of art. Best of all, it was remarkably affordable. The Switch bulb was going to cost $20…