Resulting illumination of object in complex scene

Hello! I try to solve this problem:
I have city scene with building, trees etc. It can be daytime or nighttime. And I have the “ninja” object on street. It can be in shadow or at sunlight, it can be lighted with policeman’s flashlights or hide in deep night darkness. Is there some way to determinate the 'final" illumination of the ninja to make a decision is it hide from policeman or not? (They have some sensitivity threshold denends on target “visibility”)
Is there only way to cycle through all light origins on scene and to summary lighting and shadow effects from all of them or I can try to take some final answer from ninja object itself? Maybe it shader can give me some result information?

Ok, I try search any answer in Internet and found two common ways: a) read from shader’s buffer and b) grab image into texture and analyse it. I don’t know how to do a) but it easy to do b).
So, what I do:

  1. Place a “test” plane into appropriate place in scene (A). Assign a white material to this plane.
  2. Place an additional camera that view exactly to this plane (B)
  3. Create a render texture and redirect camera view to this texture. (C - the control plane whith this texture)
  4. Create the “resulting” texture with the same size that rendering texture. I make it as white square but it not important.
  5. Use ReadPixels() to convert RenderTexture to Texture2D and assign my RenderTexture as input and “result” texture from 4. as output
  6. D is second control panel with grabbed 2d texture (former white square). E - if applay new image to texture it appear in Project with new image but it is not necessary
  7. Take a pixel’s color from new texture (F) and analyze it.
    As they say that ReadPixels() is slow operation, I do it “on demand” not on Update().
    The next step of my idea is not only take a color from plane but compare it with background to know how mach foreground is contrasts with background