Which features are used by a playwright to create a certain mood?

Think about watching a play. A play is very physical and evokes so many senses. Using sight, you can find these features in the play's description. See An Inspector Calls. Priestley sets the scene in Act 1 in order to establish the mood. From the set, what can you see? You can see an upper-class setting. What does the lighting show about what mood the playwright is trying to achieve? Now, you can link this to context. How can you relate this to the context? For An Inspector Calls, you can assume that the characters are part of a huge class disparity.