I find it hard to believe that the contribution of the reflected light by the white clouds would be a stop brighter. When I think about the intensity of the light from the white clouds compared to unobstructed sunlight, it has to pale in comparison. Therefore, I refute your hypothesis.
Edit: Actually, I have done this. Near noon I have taken incident readings with a completely blue sky. On successive days I have taken incident readings with lots of puffy white clouds but not obstructing the sun. The readings were virtually the same; the worst case was perhaps down by 1/6 stop (most likely water vapor in atmosphere). (my secondary hobby is collecting/testing light meters.)
Last edited by Fred Aspen; 04-28-2013 at 08:16 PM. Click to view previous post history.