One other thing that controls shadows is the ambient lighting (from pitch Black to none).  Try adjusting the ambient light slider and inserting a different color.  It is found  in Scene where you see Ambient, Atmosphere, Barckground, Backdrop, and Physics.  Ambient lighting plays a part in how much shadow you have.  For example, a completely black shadow as in a vaccuum of space=0% to a total overcast sky, no shadow=100% brightness.  Jan