In order to achieve a more realistic look the animator must add additional light sources to fill in the areas which would otherwise be black.

In this image an additional five lights have been added to illuminate the four walls of this room and the ceiling. These lights also fill in the dark areas on the sphere.

The effect is better but the walls look rather flat and the

sphere is getting a bit washed out in the shadows. A skilled animator can create a complicated lighting scheme that would better simulate natural light behavior but this is a difficult process involving many lights. It is also very complicated to adjust.

Compare this image with the previous one.