In the expressionistic play, "The Glass Menagerie" the gentleman caller arrives in Scene 7. There are almost sacrimonial preparations for Laura's "gentleman caller." In Scene 6 Williams stage directions have Amanda "crouched before her [Laura], adjusting the hem of a new dress, cevout and ritualistic. The dress is colored and designed by memory. A fragile, unearthly prettiness have come out in LAURA; she is like a piece of translucent glass touched by light, given a momentary radiance, not actual, not lasting.)
This description of Laura holds true in Scene 7. When the lights flicker and go out, Jim tells Laura "Candlelight is my favorite kind of light." His warm conversation with Laura is "the climax of her secret life," according to Williams's directions. As they converse, Jim smiles at Laura "with a warmth and charm which lights her invwardly with altar candles" [Stage direction]. With Jim's attentions, Laura comes alive, "nearly faint with the novelty of her emotions."
So, when Jim reveals that he is in love with another girl, Laura struggles with her emotions and she leans back. "The holy candles in the altar of LAURA'S face have been snuffed out. There is a look of almost infinite desolation." These state directions of Williams indicate that Laura's single hope for finding love has been extinguished. She is devastated in her disappointment. Her hopes are just another illusion. She is still in the darkness of loneliness and hopelessness. Nevertheless, she still has changed some; like the unicorn she has become more normal.
So, while the candlelight burns, Laura gains confidence although her confidence is as translucent as the glass animals she loves. When the lights of the altar are extinguished, Laura loses her confidence, but she still has changed, and changed more towards being normal. Without the light shining through her she, like the unicorn, can, perhaps, learn to mingle with others. For, the last stage directions have her lifting her head and smiling at her mother through her depression.