Mayor Vincent C. Gray flipped a switch Monday that turned on the last of 1,360 light-emitting diode fixtures installed in alleys throughout the District’s eight wards.

The $1 million installation project began in August 2011 and replaced bulbs that must be replaced every six to 12 months with ones that are changed every 12 years to 15 years.

“This was a major step forward,” said Gray (D), who added that the city will now embark on a similar program to replace 70,000 additional alley and streetlights.

The last light in the recent project was in an alley in Mount Pleasant where a small crowd of onlookers watched a worker rise up in bucket to install the large fixture.

Gray asked for a countdown of “3-2-1” and flipped the switch. A delay caused some angst and then the bulb flickered to cheers of relief.

“Who was the most nervous going on that one?” Gray asked to laughter.

The lights are bright, giving darkened alleys much-need illumination for safety, city officials said.

They are also more energy-efficient than their predecessors, said John Lisle, a spokesman for the District Department of Transportation.

The 1,360 new bulbs will save the city an estimated $59,000 annually in energy costs, he said.

The agency has not estimated the savings that will be realized through the reduction of maintenance, Lisle said.