When Mitch confronts Blanche in Scene Nine he recalls that she never wanted to go out with him in the daytime but always made some excuse not to go out until after six and then to some place that is not brightly lighted. She asks what he is driving at, and he tells her:
What it means is I've never had a real good look at you, Blanche. Let's turn the light on here.
Mitch tears the paper lantern off the light bulb, and Blanche utters a frightened gasp. But the bulb is not yet lighted. When Blanche says, "I don't want realism. I want magic!" Mitch laughs scornfully. According to the stage directions:
[Mitch crosses to the switch. He turns the light on and stares at her. She cries out and covers her face. He turns the light off again.]
It is pure kindness in this gentle character that he turns the light off. But he has seen what he wanted to see. She is much older than she told him she was. She has been intentionally deceiving him all along. Mitch was her last hope of maintaining a dignified existence--if she could get him to marry her. Stanley is sending her packing. She has no place to go. She drives Mitch away when he wants to force himself upon her but tells her she is not clean enough to marry. For all her faults, Blanche is a truly tragic character. We feel pity for her and fear for ourselves. The light that goes on for only moments seems to light up the human condition, which is too bad to look at for long.