Hi, I would like to get rid of the following misunderstanding. Suppose we are looking to an idealized flat diffuse emitter perpendicular to the line of sight (like a wall). If we always face this wall but slowly walk away from it, the radiant flux that we receive from a small patch of that surface is supposed to decrease according to the square distance. In fact, the solid angle spanned by this small patch will decrease according to 1/r2. However the object will appear having the same brightness instead of progressively fading to black, and become invisible....why?