Explain Juliet's use of imagery in the passage "Yon light... Thou need'st not to be gone" in Act III, Scene 5.

At the beginning of this scene, Romeo is with Juliet in
her garden, and it is daybreak.  Romeo is readying to leave, and Juliet is trying vainly
to prevent him from going, asserting that the lark he hears is in fact a nightingale; a
herald of darkness, rather than light.  When she states that “yon light is not
day-light,” but instead “some meteor that the sun exhales,” she is further attempting to
convince Romeo to stay; to convince them both that morning has not come to end their
tryst.  Romeo, somewhat jokingly, replies, “Come, death, and welcome!  Juliet wills it
so./How is’t, my soul?  let’s talk; it is not day.”  To which Juliet replies that he
must leave, having realized how selfish and short-sighted her words
were.

These images serve to emphasize how ardent the two
young lovers are, and how deeply they feel about each other – that by merely saying that
the day is not come, one could convince the other that it is so.  That one would readily
deny what he sees with his own eyes, simply because the other says that it is not the
truth.

In addition, later in this scene Juliet learns of
her arranged marriage with Paris, to take place only a few days later.  So, much as the
day comes, unstoppable, to end her time with Romeo, so does her love seem to be coming
to a permanent end with the news of this union.  And just as Juliet tries to deny the
obvious signs that the sun is rising, she attempts to deny her father and deny Paris –
yet one cannot prevent the sun from rising, and one cannot prevent one’s
fate.