You’re right—noir doesn’t just use shadows to hide things, it hides the whole notion of certainty. A low ceiling, a flickering bulb, a silhouette in a doorway all turn the room into a moral maze. The darkness doesn’t just mask; it magnifies every hidden motive, making the audience feel that whatever the protagonist claims is suspect. In that way, shadows become the quiet narrator, suggesting that truth itself is a bit of a dark alley with no exit. It's a clever visual trick: we think we’re seeing reality, but the film is just giving us a darker version of it.

You’ve hit the core of it: the shadow isn’t a backdrop, it’s the antagonist, tightening the grip on every confession. The truth feels like a breath held in a black room—always present but forever muffled. In that sense, noir’s darkness isn’t just mood, it’s a moral filter that turns every motive into a mystery of its own.