How does Williams use light and darkness as imagery in scene 6?

In Scene VI, Williams uses light and darkness to illustrate Blanche's relationship with Allan and the way it destroyed her life. It is Allan, who introduces darkness into Blanche's happy, young life. The light and darkness imagery burns brightly throughout, as Blanche compares her new love to a blinding light – something so bright that you can't actually see it at all. And this was the case with Allan, who she loved so completely and instantly that she did not realize he was gay until it was too late.

After Blanche confronts Allan, he shoots himself. As she recounts this story, we hear the polka, the Varsouviana, from the dance hall, which was playing during the scene she remembers. We are now inside her head, and the heightened unreality of the play begins to take hold. The auditory hallucination represents her guilt and obsession, and her inability to escape the past. But we hear it too, and this shared hallucination implicates us in the disintegration of Blanche's reality.