Williams often makes use of symbolism in his plays, and light is a central symbol in A Streetcar Named Desire, used primarily in relation to the main character, Blanche. It takes two major forms, candles and electric lighting – particularly the electric bulb in the main room of the Kowalski apartment – and these two forms are deliberately contrasted with one another.
The candles appear most prominently at Blanche’s failed birthday party and earlier when she entertains Mitch alone. Blanche remarks to Mitch that since her disastrous marriage there’s never been any light 'stronger' for her than ‘this kitchen candle’ (scene 6). Life for her has become emotionally dimmed. But candles also signify romance and tenderness and beauty, the kind of exquisite qualities that Blanche professes to attach so much importance to. The electric bulb, on the other hand, stands for the more unpleasant side of life; it is the harsh glare of reality, which strips away all pretensions and pretence, exposing ugly truths.
It is not surprising that Blanche, who so often attempts to weave illusions, wants the light bulb covered up:
I can’t stand a naked light bulb, any more than I can a rude remark or vulgar action.(Scene 3)
It is even more significant that Mitch is the one she asks to cover the bulb, with a paper lantern she has brought. Mitch is the man she hopes to marry, to bring true romance into her life and also at last to provide her with some security. However, this does not happen; Mitch ends up disenchanted with her when he finds out about her sordid past and symbolically tears off the lantern to expose her to the glare of reality.
In fact, the lantern is explicitly compared to Blanche herself, at the very end; when Stanley roughly thrusts it at her, asking if she wants to take it away with her, it is said that ‘she cries out as if the lantern was herself’ (Scene 11).
Blanche’s placing of the lantern over the bulb signifies how she tries to dress up reality, which for her is altogether too grim, with beauty and art and romance. It is true that she is a liar and hypocrite but we can also understand and pity her, and see her efforts to change reality as springing not just from willful deception but a kind of pathetic idealism.
I’ll tell you what I want. Magic! …. Yes, yes, magic! I try to give that to people. I misrepresent things to them. I don’t tell the truth. I tell what ought to be the truth. And if that is sinful, then let me be damned for it! (Scene 9)