In December, the Nobel Prize for physics went to the team behind a significant invention: the blue light-emitting diode (LED). While red and green LEDs have been around since the 1960s, figuring out how to make blue diodes bright enough stumped engineers until the early nineties. That advance—enabled by high-quality gallium nitride—quickly led to another. By converting blue light to white, engineers produced the crisp beams now ubiquitous in computer screens and smartphones. More recently, they found yet another application: street lamps. To date, Los Angeles has swapped in 155,000 LED fixtures, a move that has reduced both municipal energy bills and light pollution. Ed Ebrahimian, who directs L.A.'s Bureau of Street Lighting, says the benefits are a no-brainer for cities. "We're at the tip of an iceberg," he says. "I think we are going to see a tremendous conversion happening in the next five to 10 years."