We can never know the exact intention behind an author's writing or the literary devices they employ; however, we can examine the effect that these devices have and what they add to the work to infer the author's intention. In Lord Byron's poem "She Walks in Beauty," he relies heavily on contrast throughout, which in effect creates stark imagery while also juxtaposing the poem with much love poetry of the time.
Byron most frequently uses the contrast between light and dark in the poem. In describing the woman's beauty, he suggests that her perfection lies in the balance between the light and dark that she possesses. She is like a cloudless, starry night, which is at once dark and sprinkled with radiant light:
And all that's best of dark and bright
Meet in her aspect and her eyes.
He continues to suggest that she is raven-haired but fair in complexion, and he says that altering the balance between light and dark within her would impair her beauty. Yet, this is the only physical description we get of the woman, and so it seems that the lightness and darkness Byron is referring to is both physical and metaphorical. This play between light and dark creates an inherently visual and emotional effect for the reader.
By focusing on this contrast between light and dark in the woman, Byron also presents himself somewhat in opposition to love poetry at the time. This poem was written during the Romantic period, a time when poetry was marked by strong idealism and passionate emotion. Love poetry sought to venerate the object of affection and admit to nothing besides absolute perfection. And although he certainly presents this woman as an ideal and as "perfect," just as she is, Byron in this poem takes a slightly different tack, rather like Shakespeare in his Sonnet 130. He presents a woman who does not radiate like the sun or match the other fair-haired goddesses described in his contemporaries' work. Rather, he presents something more complicated: a woman whose beauty and allure is derived from the balance between light and dark within her and the goodness deep within her soul.