Lighting designers say a light is motivated if the source is understood by the viewer. In a film, comic book, or illustrated book, this can be important in setting a mood and making the lighting look convincing.
In this clip from Hiyao Miyazaki’s Spirited Away, the girl enters a corridor where she sees multiple cast shadows projected on a wall. The shadows flicker on and off for no apparent reason. Up until this point the light is unmotivated.
With the lighting now fully motivated, the lighting designer has some freedom for the remainder of the scene. The remaining shots don’t have to make perfectly logical sense. Most of the later shots have single shadows cast to the side or even nearly straight downward.
What’s important in the later shots is clarity of action and expression in the service of the story. Showing those multiple flickering cast shadows again would not only be unnecessary, it would be confusing.
An individual painting can have motivated light as well. At the top of this painting by Peder Severin Kroyer, we can see light flooding in through an upper window. That glimpse of the source allows us to understand where the sharp spots of light on the work table come from.