BLANCHE And turn that over-light off! Turn that off! I won’t be looked at in this merciless glare! (1.75)
As you can read in "Symbols, Imagery, Allegory," light comes to mean a lot of different things in A Streetcar Named Desire. This first instance is the most important, and reveals Blanche’s fear of showing her age.
BLANCHE …You know I haven’t put on one ounce in ten years, Stella? I weigh what I weighed the summer you left Belle Reve. The summer Dad died and you left us… (1.123)
For Blanche, looking good is all about maintaining her youth and the illusion that nothing has changed.
STELLA And admire her dress and tell her she’s looking wonderful That’s important with Blanche. Her little weakness! (2.22)
Blanche isn’t fooling anybody, least of all her sister. Those around her propagate her self-delusion.
STANLEY Compliments to women about their looks. I never met a woman that didn’t know if she was good-looking or not without being told, and some of them give themselves credit for more than they’ve got. I once went out with a doll who said to me, "I am the glamorous type, I am the glamorous type!" I said. "So what?" (2.103)
This is where the conflict in Streetcar really rises to the surface – from what we know about their characters, it’s basically impossible for these two to coexist.
BLANCHE …After all, a woman’s charm is fifty percent illusion… (2.129)
As is Blanche’s self-image and her veneer of innocent charm. What’s so interesting is that she KNOWS she’s full of it, but continues to operate on a level of fantasy anyway. Or, as she later says to Mitch, "I don’t want realism — I want magic!"
STANLEY Well this somebody named Shaw is under the impression he met you in Laurel, but I figure he must have got you mixed up with some other party because this other party is someone he met at a hotel called the Flamingo. […] BLANCHE I’m afraid he does have me mixed up with this "other party." The Hotel Flamingo is not the sort of establishment I would dare to be seen in! (5.38-9)
Now we know that Blanche isn’t just suffering from self-image issues – her reputation has in fact been completely destroyed since the days of her youth.
BLANCHE It isn’t enough to be soft. You’ve got to be soft and attractive. And I – I’m fading now! I don’t know how much longer I can turn the trick. (5.60)
Blanche’s "softness" may have been an asset in her youth, but it’s certainly a liability now. It means that she isn’t a strong enough person to deal with men like Stanley.
STELLA She is. She was. You didn’t know Blanche as a girl. Nobody, nobody was as tender and trusting as she was. But people like you abused her, and forced her to change. (8.50)
Blanche’s charms helped her socially when she was younger, but hurt her after she matured into adulthood. Stanley’s pragmatism is far more suited to the real world than Blanche’s poetry and flirtations.
BLANCHE A cultivated woman, a woman of intelligence and breeding can enrich a man’s life – immeasurably! I have those things to offer, and this doesn’t take them away. Physical beauty is passing. A transitory possession. But beauty of the mind and richness of the spirit and tenderness of the heart – and I have all of those things. […] But I have been foolish - casting my pearls before swine! (10.44)
Look at the intensity of Blanche’s self-deception moments before she is finally "broken" by Stanley.