shadow monster in search of light

My "shadow monsters" are animated textures on planes that slide around the floor. I would like them to all move towards lights that the player places in whichever place they want.

Originally I thought to have them rotate with a raycast on each until the ray hit a light and then have it move forward in that direction, but then I was looking at the RaycastHit and I don't believe it can hit a light as it doesn't have a collider or rigidbody. So, now I am unsure how to go about this.

Any ideas?

Looks like you have to create your own implementation of light detecting.

Knowing a little about your monsters I can suggest you to project user light source origin on to planes where monsters are. So this will be a point nearest to the light source. And then make your monsters to move to this point.

You want these "shadows" to move along the floors, walls, etc. until they reach the actual light, or until they reach the point of closest approach of the light to the surface they are already on (which is what Anton Petrov's suggestion will do)?

If you want the shadows to move from wall to floor until they actually touch the light source (as opposed to being bound to their original plane), you actually had the right idea in your own question. Lights don't have collider, but you can create an empty object and put both the light and the collider in there. Then you can raycast on that layer only (if you want to avoid other things colliding with the light/shadows) and get a direction to the light. Project that direction onto your plane and the shadow should move on the plane towards the light. I'll see if I can't clarify with some code later...

Why not just have the lights tagged "Light" and have the monsters look towards any game object with the tag "Light". Just add a constant force to the monster (5, 0, 0) and you should be good to go!