Lighting.

Lighting in movies can be used to create depth, ambiance, and mood to the visual portrayal of events.

Functions of the different lights:
The Key Light is the brightest and most influential light.
The Back Light helps counter the effect of the Key Light, or can be used to create a silhouette.
The Filler Light helps to soften the harsh shadows that the use of Key and Back Light creates.

Different types of lighting:
Underlighting - when the main source of light come from below the subject. It is primarily used in thrillers and horror films.
Top Lighting - when the main source of lighting comes from above, highlighting the subject very angularly. Is thus used to create a dramatic and glamorous look.
Back Lighting - when the only source of light is from behind the subject, perhaps a window, so a silhouette is created.
Low-Key Light - creates using only the Key and Back Lights. It produces a sharp contrast of light and dark areas on the screen, as very deep, distinct shadows are formed.
High-Key Lighting - More filler lights are used to illuminate the subject completely, reducing shadows and thus lighting appears natural.