What is the symbol of the searchlight in A Streetcar Named Desire?Blanche: "I’d suddenly said--“I saw! I know! You disgust me” And then the...

I think that the issue of light is a larger element in the
statement.  Blanche is a character who is afraid of light.  The idea of light,
illumination, is something that would tear away at her like a razor because it would
highlight all of her falsehoods, as transparency would reveal her to be something that
she wishes not to be. In the quote that describes her husband's suicide, the light that
was "turned off" represented her need to recreate her identity, to embrace that which
could be constructed with as little "light" or truth as "this - kitchen - candle." 
Blanche was profoundly impacted by her closeted husband's suicide.  The idea of a
"closeted" husband brings the light issue back into even more relevancy.  The death of
her husband brought with it a need to recreate a facade and state of being that could
only exist in supposition and shadows, something that would not be able to withstand the
white, hot glare of modern scrutiny.  The "searchlight" was the last light of this world
that would damage Blanche's own attempt at creation.  From that point on, from the death
of her husband, Blanche felt that the creation of her own persona was vitally important,
something that could not be done without darkness and stealth, a sense of deception to
the world and, of course, to herself.