Virtually every horror movie known to mankind features at least one scene where fear is portrayed in the form of shifting shadows. When this on screen anxiety shows up in real life it is known as Sciophobia.
This fear almost always goes back to anxiety related to the identity of the source of the shadow when the mind conjures a worst case scenario immediately. As with most fears this phobia is often introduced by someone who has their own personal fear of shadows. If this is not a genetic predisposition then it is the result of observed behavior.
It can also be a fear assumed through a traumatic experience precipitated by the observation of a shadow that became an experience that may have brought pain and suffering. This could be physical violence at the hands of someone else or even an animal.
An individual with a fear of shadows will likely be more prone to remain in well lit homes with very little subdued lighting. They may be inclined to insist on premium security measures and may resist sleeping in a darkened room.
The fear of shadows may make it difficult for the phobic personality to concentrate on conversations in social settings because they will remain wary of any potential shift in shadow.
Individuals with this fear can find help in learning that shadows are always exaggerated well beyond the size and scope of the object casting the shadow. This may mean that the individual may need to experience this phenomenon in a safe environment with a therapist.