With the recent storms, the City has experienced some short power outages. Back in August, we ran a post on "blacked out" signals. California law requires that when drivers come upon a signal light that is not working, blacked out, or otherwise inoperative, the driver shall STOP their vehicle just like a stop sign. So, if you come upon a traffic light that is not working, stop at the limit line unless directed to do otherwise by a police officer. The only exception to the law is when new signals are being installed. The signal will still be covered in some way, usually with cardboard. Drivers may proceed as usual in that situation while obeying the rules of the road.
Refer to the link for the previous post and an a link to the actual CVC section.