Words that sound alike, but have a different meaning

They are called Homonyms.

For example, air and heir

air is the gaseous substance surrounding the earth and heir is the person who will receives the wealth of that person's death

In "She Walks in Beauty," the speaker employs a series of binaries, or contrasts, to characterize the woman's beauty. Light and dark are among the two of the binaries in the poem.

The lines which compares light and dark to describe the women in " She walks in beauty," are:

SHE walks in beauty, like the night

Of cloudless climes and starry skies,

And all that's best of dark and bright

Meets in her aspect and her eyes;

Thus mellow'd to that tender light

Which Heaven to gaudy day denies.

The poem “She Walks In Beauty” by Lord Byron is about a woman who is very beautiful and charming. The poet speaks about her beauty which is “pure” and “sweet.” He compares her beauty with the dark things present in nature. He also builds a contrast between light and dark, day and night to compare her beauty with. The poem is about her physical, spiritual and intellectual beauty.