The changeover began in October 2013, toward the end of the Bloomberg administration. Having replaced incandescent bulbs with compact fluorescent curlicues in many city buildings, officials wanted to bring a similar transformation to the streets.

After testing LEDs on highways and in parks since 2011, the Transportation Department began the first neighborhood installations last month, bringing hundreds of new lamps to the Kensington and Windsor Terrace sections of south Brooklyn.

“With the city reducing its overall carbon footprint by 30 percent by 2030, at our agency, this is one of the biggest contributions we can make,” the first deputy commissioner of the Transportation Department, Lori A. Ardito, said. “We’re always looking for improvements and innovations we can make on the streets, whether it is bike lanes or new parking meters, and the new streetlights are part of that.”

The city is spending $75 million on the new lights, embedded in LED-compatible “cobra head” fixtures affixed to existing light poles. Annually, they will save $6 million on energy costs and $8 million on maintenance because LEDs last up to 20 years, two to four times as long as most sodium-vapor units.

“To the degree you can make the city’s operations more sustainable, it just pays so many dividends,” said the LED leader in the Bloomberg administration, Margaret Newman. But she said that had the city done a little more promotion of the new lights, especially in eco-conscious Brooklyn, they would have been more readily embraced.

Jim Knowles, a longtime resident sipping a beer at Rhythm & Booze, failed to see the value. “They think we’re mad?” he said. “They’re lucky they didn’t start in Park Slope.” The lights were glaring not only outside his favorite bar but also outside his home on 18th Street.