In part 3, the reader is introduced to Sir Lancelot, and almost every image associated with him concerns brightness and light. The sun "came dazzling" through the leaves when he rides, and it "flam'd" upon his armor. His shield "sparkled," and his "gemmy bridle glitter'd" like stars in a "golden Galaxy." His baldric is "blazon'd," and his saddle is "thick-jewell'd" so that it "shone." His helmet and its feather "burn'd like one burning flame together," and his presence is compared to the light trailed by "bome bearded meteor" beneath the "starry clusters bright" over Shalott. His horse has "burnish'd hooves" and his brow "glow'd" in the sunlight. In short, Sir Lancelot is associated with burning and brightness over and over, and this begins to change the mood of the poem which, before, had been tragic but relatively serene. Fire and light can be beautiful, but they can also be dangerous, just as the sight of Sir Lancelot is so beautiful to the Lady of Shalott that she turns immediately to look at her window, bringing down the curse that will end her life. She is drawn to him, and she is figuratively burned by his appearance.

In addition, lines 1–4 and 6–8 of final stanza of part 3 are written in regular iambic tetrameter, though these lines in other stanzas (so far) do vary at times between iambic tetrameter and trochaic tetrameter. Suddenly, the poem shifts into a much more regular and predictably rhythmic pattern, so that it feels as though the Lady of Shalott's fate is sealed; it has become inevitable, like the regular rhythm of these lines.