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Like me, you might have welcomed this development. LEDs are, after all, the most energy-efficient lighting option on the market. They can last twice as long as ordinary sodium-vapor streetlights, and their prices have dropped to within range of the competition.

If the switch to LEDs had needed any more support, it came from growing evidence about climate change. In the United States, Street Light accounts for a whopping 30 percent of all the energy used to generate electricity for outdoor lighting. Another 60 percent goes toward lighting parking lots and garages, and much of that energy is still produced by fossil-fired power plants. Consultants at the firm Navigant, in Chicago, have estimated that the United States could save 662 trillion British thermal units—the energy needed to power 5.8 million typical U.S. homes for one year—by converting all remaining non-LED outdoor lighting to LEDs.

Armed with statistics like these, and a mandate to cut energy use wherever they can, municipalities across the United States have installed more than 5.7 million outdoor LED street and area lights. Other towns and cities in Canada, Europe, and Asia have added millions more over the past decade. Amid this rush to adopt outdoor LEDs, the U.S. Department of Energy (DOE) stressed energy efficiency as the biggest advantage of the new technology while cautioning cities to also consider light output and color quality. But now that ordinary folks have got an eyeful of those new lights, some municipalities are coming down with a case of the early-adopter blues.

Some communities, too, are using smart lighting controls to minimize light pollution. They are welcome changes, but they’re happening none too soon: An estimated 10 percent of all outdoor lighting in the United States was switched over to an earlier generation of LEDs, which included those problematic blue-rich varieties, at a potential cost of billions of dollars.

The episode invites a few questions: How did an energy-saving technology that looked so promising wind up irritating so many people? Why has it taken so long for the impacts of blue-rich lighting to become widely known? And why did blue-rich LEDs so captivate municipal lighting engineers long before better options reached the market?

The cheapest and most efficient way to make white light from an LED is to shine light from one or more powerful blue LEDs onto compounds called phosphors that absorb blue light and emit yellow light. This light combines with the remaining blue light from the LED to appear white to the eye.

The resulting shade of white depends on the blend of blue from the LED and yellow from the phosphor. It’s measured on the color-temperature scale, which corresponds to the temperature (in kelvins) of a “black body,” which is an object that absorbs all the electromagnetic radiation it encounters and emits a similar mixture of colors. Early “white” LEDs developed in 1997 at Nichia Chemical Industries, in Japan, (now known as Nichia Corp.) were quite blue: They emitted more than 45 percent blue light, corresponding to 8,000 K. That’s even bluer than the color temperature of summer daylight, and it looks harsh to the eye.