The strongest metaphor used in Romeo and Juliet has to do with light and dark.
Romeo compares Juliet to the moon, the source of light in the darkened sky, though not to burning torches and to the sun rising in the morning. She is the source of light, or hope, in his world, which in a time of "ancient grudge" and "new mutiny" must be a struggle to find.
“But, soft! what light through yonder window breaks?
It is the east, and Juliet is the sun.
Arise, fair sun, and kill the envious moon,
Who is already sick and pale with grief,
That thou, her maid, art far more fair than she.
Be not her maid, since she is envious;
Her vestal livery is but sick and green
And none but fools do wear it; cast it off.
It is my lady, O, it is my love!
Oh, that she knew she were!”
For Romeo, good things seem to happen in the darkness; it is where he meets Juliet at the ball, and again at the balcony. He spends the night with her after killing Tybalt. However, when daylight breaks, things don't tend to go so well. He kills Tybalt in the daytime, and he hears of Juliet's "death" during the day also.
When Romeo is to leave Juliet's bedroom in the morning they have a prolonged discussion of how they wish to change night and day, or light and dark:
Jul. Wilt thou be gone? it is not yet near day:
It was the nightingale, and not the lark,
That pierc'd the fearful hollow of thine ear;
Nightly she sings on yon pomegranate tree:
Believe me, love, it was the nightingale.
Rom. It was the lark, the herald of the morn,
No nightingale: look, love, what envious streaks
Do lace the severing clouds in yonder east:
Night's candles are burnt out, and jocund day
Stands tiptoe on the misty mountain tops:
I must be gone and live, or stay and die.
Jul. Yon light is not daylight, I know it, I:
It is some meteor that the sun exhales,
To be to thee this night a torch-bearer,
And light thee on thy way to Mantua:
Therefore stay yet; thou need'st not to be gone,
Rom. Let me be ta'en,, let me be put to death;
I am content, so thou wilt have it so.
I'll say yon grey is not the morning's eye,
'T is but the pale reflex of Cynthia's brow;
Nor that is not the lark, whose notes do beat
The vaulty heaven so high above our heads:
I have more care to stay than will to go:
Come, death, and welcome! Juliet wills it so,
How is't my soul? let's talk; it is not day.
Jul. It is, it is; hie hence, be gone, away!
It is the lark that sings so out of tune,
Straining harsh discords and unpleasing sharps.
Some say the lark makes sweet division;
This doth not so, for she divideth us:
Some say the lark and loathed toad change eyes;
O! now I would they had changed voices too,
Since arm from arm that voice doth us affray,
Hunting thee hence with hunt's up to the day.
O! now be gone; more light and light it grows.
Rom. More light and light; more dark and dark our woes.”