People don’t often think about the shadow. The shadow is incredibly important. Not only does it tell you which way the light is coming from, it also tells you if the light source is singular or multiple. The shadow can tell you what time of day it is. If the shadow is long, the time is either closer to sunrise and sunset. If the shadow is short, the time is closer to noon.
Here are a couple of more things to think about with the shadow.
1 - If I am focusing lights and I do not want the light to hit a piece of scenery or a screen, consider where the shadow is going. Move the light so that the shadow is not effecting that piece of scenery and voilà! You are not lighting the piece that you did not want to light.
2 - If you want to make sure that you see a real directional light, then make sure you have a singular shadow. Multiple light sources blend out shadows. Go for that singular shadow and your light will look very directional.
3 - If you need more light on the shadow side of a face, but you don’t want to lose the directionality of the light, choose a shadow color that is a shade of the source of light. You can then fill in the shadow part of the face without effecting the composition of the directionality