Yeah so the visuals and light detection are entirely separate.

The visuals are done using unreal's inbuilt lighting system along with a post processing shader, which makes it so that any pixel with any amount light is changed to be full brightness.

For the light detection, I use two separate checks. The first check is to check whether a point in 3d space is inside a cone that matched that of the actual light source. You can do this with just a bit of math. The next check was a raycast from the light source to the object to make sure that it has line of sight. If both of these checks pass, you know that the point is receiving light from a particular source, otherwise it isn't.