A sun blade was a magic sword whose blade consisted of pure sunlight. When deactivated, it appeared to be a longsword hilt with no blade. A creature attuned to it could cause a bright radiant blade to appear or disappear by force of will.
Sun blades were extremely light, allowing them to be wielded even by users who possessed little strength. The light emitted by these blades were actual sunlight, and its radiant energy was particularly damaging to Undead.