it would look better if you created a custom hdri map of an area like that on a sunny day, then placed the sphere on the plane in a box with holes in thoes two areas.  other than that you might want to use a scene that has more objects in the middle so you can get a more percise idea of where the shadows would be where the sphere is.  there are also some radiosity problems, the bottom of the ball would be blacker and the top should be lighter. 

another important thing is the angle of the shadows on the ball, try moving the area lights a little left of the table