* His Mysterious and Unseen Nature: The knight is initially described as a figure shrouded in shadow, a "shadow" himself. This emphasizes his unknown and mysterious nature, a stranger who arrives in a world that the Lady of Shalott has only ever seen through a mirror. He represents the unknown and the allure of the "outside world," which is both enticing and dangerous.
* His Connection to the "Real World": The use of darkness contrasts with the Lady's world, which is depicted as light and enclosed within her tower. By associating the knight with darkness, Tennyson suggests a connection to the "real world" outside her window. This world is portrayed as full of danger and uncertainty, but also as a place of life and experience that the Lady yearns for.
* His Role as a Catalyst for Change: The knight's arrival signifies a turning point in the Lady's life. He awakens a desire within her for a different life, one that is both exciting and potentially destructive. The darkness surrounding him foreshadows the tragic consequences of her decision to leave her tower.
* The Shadow of Death: In a broader sense, the use of darkness symbolizes the inevitable shadow of death that hangs over the Lady's existence. The knight's presence, while initially filled with promise, ultimately leads her to a fatal destiny. The darkness associated with him becomes a premonition of her own impending doom.
Ultimately, the use of darkness in describing the knight in "The Lady of Shalott" is not simply a stylistic choice, but a deliberate and symbolic device that enriches the poem's themes of isolation, longing, and the dangers of venturing into the unknown.