LOS ANGELES — In 2014, Los Angeles cut its annual carbon emissions by 43% and saved $9 million in energy costs by replacing the bulbs in more than half of the city's street lamps with light-emitting diodes.

That year, the Nobel Prize in physics went to three scientists whose work made those LEDs possible. "As about one fourth of world electricity consumption is used for lighting purposes, the LEDs contribute to saving the Earth's resources," the Nobel committee explained when it announced the award.

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