The creation of a dark atmosphere or mood is important in noir' film. The use of dim lighting, and lighting used to specifically enhance shadows greatly accentuates this kind of mood. Almost every scene in the film contains an essence of darkness. Dark, gloomy shadows are recurrently used throughout the film. I mentioned in the review that one of the brilliant things about this film lies in what the characters do not know.
Shadows help to create the feeling of the unknown or that something is hidden.
This is a great example of how a film's composition can reflect characterization. There are absolutely no low points in this film. Everything from individual shots, to whole scenes and sequences to composition and camera movements, angles and distances is pure cinema.