The lights were restored to the Washington Monument Monday evening, after electricians traced the problem to a ground fault, the National Park Service reported.
The lights had gone out earlier Monday. It was the second time since the beginning of the year that the national icon went dark at night.
The problem Monday was unrelated to the problem last week, officials said.
The lights went out Jan. 3. That time, officials blamed the clock in the Washington Monument's automated lighting system.
The monument has had plenty of systems trouble lately. It has been closed since August due to ongoing problems with its elevator.
In December, officials said they would spend $2 million to $3 million to fix the elevator, and planned to reopen the monument to visitors in 2019.
A Park Service spokesman said in an update Tuesday afternoon that electricians and Pepco electricity utility workers would be on hand Tuesday evening to be sure the lights come on as scheduled.
The lights were on as of 5:15 p.m. Tuesday.