Romeo draws upon light imagery to describe Juliet. We see this most notably in the famous balcony scene in act II, scene ii, when he likens Juliet to the sun rising in the East. He then goes on to describe the light that seems to emanate from Juliet's extraordinary beauty:

The brightness of her cheek would shame those stars
As daylight doth a lamp.

Just as daylight is brighter than any lamp, so too does Juliet's beauty shine more brightly than the stars in the heavens.

In contrast, Juliet uses imagery associated with darkness to describe Romeo. In her soliloquy at the beginning of act III, scene ii, she draws upon Greek mythology to express her impatient longing for the night when Romeo will be at her side during their honeymoon:

Gallop apace, you fiery-footed steeds,
Towards Phoebus’ lodging. Such a wagoner
As Phaëton would whip you to the west
And bring in cloudy night immediately.

Later on, Juliet uses the imagery of the nightingale, a bird associated with night, to express her wish that the night will go on just that little bit longer before the dawn breaks which will usher in the day when Romeo will be forced to leave Verona for exile in Mantua:

It was the nightingale, and not the lark,
That pierced the fearful hollow of thine ear.
Nightly she sings on yond pomegranate tree. (Act III, Scene v).