typically, Blanche avoids standing in bright lights where she can clearly be seen - except for during the poker night, when she wants to be seen by the men - in order to maintain her vanity
symbolises the reality of Blanche's past
dim light reflects Blanche's state of mind after and since her husband died, whereas bright light is indicative of her youthful, sexual innocence
Blanche covers the exposed light bulb in the Kowalski's apartment with a paper lantern, and refuses to go out with Mitch in the day