Legal Question in Real Estate Law in California

Well for starters you can't sue someone else's insurance company. Since the late 80s it has been the bright-line crystal-clear law in California that insurance companies owe NO duty of any kind to third-parties. Their legal obligations run only to their insureds.

You are also going to have to prove causation. The roofer had to have done something you can prove was wrongful or negligent that caused the light to fall. If they are right, and the light was not properly installed, or even if you just can't come up with admissible evidence that they did something wrong, you will lose a lawsuit.

The much better course is just to make a claim to your own insurance company. They should pay for the repair and then if they think someone did something wrong and they think they can prove it and it's worth their trouble for how much it costs them, then they will have the right to sue whomever they think is responsible for reimbursement - not your problem.