Ann Arbor, Mich., home to the main campus of the University of Michigan, announced that it intends to become the first U.S. city to convert all of its downtown streetlights to LEDs (light-emitting diodes). The energy-saving lights use half the energy and are expected to last five times as long. In two years, when the city of 113,000 completes the conversion of all 1,046 streetlights, they’ll cut CO2 emissions by about 2,425 tons a year. Ann Arbor has already converted all its traffic lights to LEDs.