Light is usually a comfort, but here it feels like an intruder. The first half of the poem describes what light does: it floods a room, exposes lies, chases shadows, reveals dreams and announces the morning. Nothing sounds harmful yet, though the word "exposing" hints at where things are heading. Then the speaker turns on it. Light "pierces" and "burns," and the poem shifts from description to a plea: "Be gone, light, / From this dark heart."
Light seems to stand for exposure, being seen and known. The speaker carries "too many hidden scars" and fears that if they are revealed, the pain will be unbearable. Darkness feels like protection, a place to keep wounds private. The last line, "I will drown in my own tears," shows how close to breaking they are.
The mood is quiet, tense and vulnerable. Short lines and plain statements make the speaker sound guarded, almost whispering, as they beg not to be uncovered.