Anyway to use light information as a mask? Is there anyway to set up a node mask that sees how much light is hitting an object and adjusts its transparency based on how lit an area is?

Like if I had a textured ball, and wanted the texture to lower its opacity when a lamp shines onto it, but moved the camera around to the dark areas the texture is still visible . Is this possible in Blender?
Sort of. 

Create a light. Create an Empty and use the Copy Location constraint with the light as the target.

Use the following node tree as the texture for the object. Be sure to note the Empty selected as the Object in the Texture Coordinate node.



In this case, I'm just mixing between red and blue. Transparency doesn't seem to work, but you could create a second view layer, use this texture with an emission shader and use that as a mask in the compositor.