Inspector Goole's entrance is very important as it affects the whole mood and atmosphere. It says in the stage directions that the lighting should be pink and intimate, as it is a joyful occasion for the Birling family, until the Inspector arrives and then it should change to be brighter and harder. I think this is because Priestly wants to create a noticeably colder atmosphere upon the Inspectors presence.
In the Royal National Theatre production of "An Inspector Calls", when the Inspector emerged onto the stage, the Birlings' house split into two allowing him in. Metaphorically, this represents how the Inspector, later on in the play divides, morally, the older and younger generations of the Birling family. The family is also exposed by the use of light, "Give us more light." This is symbolic because not only does it let you enter the Birlings' world but it also reveals to the audience their true inner characters.
The Inspector's entrance clearly affects the mood of the play. In the initial scene directions Priestley instructed that the lighting should become "brighter and harder" when the Inspector arrives, which gives him an advantage, for the family can no longer hide behind the rosy glow.
The Inspector makes it clear that his purpose is to establish exactly whom it is that made "a nasty mess" of Eva Smith's life. I noticed that he does not spare the Birlings any of the harsh images of the suicide victim, and the audience realise that he is very single-minded in pursuing his chosen line of investigation. He is not like a normal Police Officer in the way that they show respect for people they encounter, whereas, he is sometimes quite rude and ill mannered to the Birlings which shocks Mrs. Birling - "I beg your pardon!" Priestley...