The signs were first allowed under a 2006 deal between the city of Los Angeles and advertising companies Clear Channel Outdoor, which owns 67 of the signs, and CBS Outdoor.
The deal ended a legal challenge to a sign ordinance, with the city agreeing to permit as many as 840 signs to be converted to electronic formats, Los Angeles Times reported Saturday.
A smaller company, Summit Media, challenged that arrangement as a sweetheart deal that allowed the larger companies to break the law at the expense of smaller companies.
A three-judge panel agreed with Summit in December but the larger companies have kept up legal challenges to the ruling, and are pushing for the city to change its existing sign laws.
An attorney for Summit, Timothy Alger, said he appreciated Judge Terry Green's ruling, but also said he was considering taking the case a step further by pursuing legal action to have the signs dismantled.
"The fact of the matter is, CBS, Clear Channel and the city were all wrongdoers in this thing. They collaborated to enter into an illegal contract," Alger said.
The ruling was praised by activists who see billboards as eyesores and complain that the electronic signs are invasive, as they shine into residential neighborhoods.
"This is what we've been waiting for now for six years. I'm going to be out there personally at 5 o'clock to watch it go dark," said Dennis Hathaway, president of the Coalition to Ban Billboard Blight, referring to the Monday deadline ordered by the court.