In A Streetcar Named Desire, written by Tennessee Williams in 1947 and then later directed by Elia Kazan in 1951, Blanche Dubois's (played by Vivien Leigh) best friend and worst enemy is darkness. She uses darkness as a tool to hide her true identity and age, but in the end it becomes her undoing.
Blanche DuBois has a multitude of problems, and the fact that she is getting older is really very low down on the list. But for some reason she focuses on hiding her identity through the use of shadows and the absence of light. She refuses to stand in direct light and even goes so far as to cover lights at her sister Stella Kowalski's (depicted by Kim Hunter) apartment. She lies to her fiancé, Harold "Mitch" Mitchell (portrayed by Karl Malden), about her age and will not go out with him during the day so that he cannot see her for who she really is. This is the way she uses darkness as her "friend," but other creatures have done this same thing, such as vampires, witches and other creatures of evil. While this is not truly pertinent to this essay, it is interesting to keep in mind that typically in literature and in films darkness is used to represent evil or evil creatures. This makes one wonder about Blanche when one keeps this fact in mind.
Blanche uses lights as her friend in the beginning, but by the end of the play/movie her "friend" becomes her worst enemy. While Blanche's sister is in the hospital having a baby her brother-in-law, Stanley Kowalski (played by Marlon Brando) rapes her because he realizes she is losing her grasp on reality. Two types of darkness existed in this situation, a figurative and literal darkness. Blanche losing her grasp on reality is the figurative darkness. Reality no longer exists for her, so it can be said that she lives in darkness. Her rape takes place in the literal darkness; but it pushes her further in to the figurative darkness, where she seems to permanently exist at the end of the movie and play.
When the lights go out, evil usually lurks. Unfortunately for Blanche, she forgot that fact and tried to manipulate darkness to her advantage hiding in the shadows and refusing to be seen in direct light. But instead of darkness serving as a friend, it used and abused her and permanently trapped her inside its domain.