What is bright with the radiance of intellect; not darkened or confused by delirium or madness; marked by the regular operations of reason; as, a lucid interval. See Luminous called?

lucid — Bright with the radiance of intellect; not darkened or confused by delirium or madness; marked by the regular operations of reason; as, a lucid interval. See Luminous. (Webster's 1913.)

Sources