Render Target read shadows

I am trying to set up a render target for an actor type which I can use to read pixels from. From the pixel data I want to see if its currently in the shadows. I know this is a slow process, but I want to try something using this approach. My problem is I do not know how to set up this properly with the render target, so it represents the current “state” of the texture. All it is currently reading is the colors of the original render target and it is not affected by light