There are a few caveats to the law, particularly what's required for tinting to be considered legal. Before going to add that darker tint, avoid the ticket and brush up on California's law.

California window tint law restricts windshield tint on top 4 inches. Front-side windows must have 70% light transmission or more. Back side windows and rear window may have any tint darkness.

The lower the number, the darker the tint. The Car Tint Law website has a useful slider that shows what different levels of tinting look like. Toggle on the background image to get the full effect.