The lights that illuminate the Washington Monument are on the blink, and authorities are still trying to figure out what caused the problem.

Mike Litterst, a spokesman for the National Park Service, which oversees the monument, said the lights went out around 7 p.m. Tuesday. The lights used for safety and aviation precautions were not impacted, he said.

The initial thought was the blackout had “something to do with the automated light system,” according to Litterst. Pepco teams investigated, he said, but it was quickly clear that it was not a problem “on their end.”

The lights were on when park service electricians arrived Wednesday morning, Litterst said, giving them an “indication the lighting system’s clock is likely out of sync.” Crews were working to fix it and the lights are expected to be back to normal by this evening, according to Litterst.

The problem comes as the Washington Monument is closed indefinitely because of ongoing problems with its elevator. The 555-foot-tall, marble-and-granite obelisk was damaged in a 2011 earthquake and was repaired. But the elevator has a long history of troubles, even before the quake.