Illumination-based Stealth System using built-in dynamic shadows?

Hi I was wondering if there was a way to have unity's built in lights cast an invisible shadow-volume to be used as some trigger to set an illumination-level float, I've currently been trying to simulate something similar by attaching trigger cylinders to objects and having those objects be aligned with the light's position and they would simulate illumination but what if you are hiding behind a wall and this trigger still touches you but in the room you are currently in you are in pitch-black darkness? Also I'm not sure how I would get another object to check the current number on a different object and then return results to be used in an if-statement. I feel really stumped as of now but I felt like I was onto something, but alas.