“illumination” in every sense, used in the ordinary sense of giving natural light (Psalm 97:4 the King James Version; see also Ezra 9:8) or as a sign of health and vigor (1 Samuel 14:27, 29). “His eyes were enlightened,” literally, “became bright.” He had become weary and faint with the day’s exertions and anxieties, and now recovers (Job 33:30 and compare Psalm 13:3). Thus, in sickness and grief, the eyes are dull and heavy; dying eyes are glazed; but health and joy render them bright and sparkling, as with a light from within.
(2) In Psalm 18:28 the King James Version, The word nāghah, figuratively describes the believer’s deliverance from the gloom of adversity and the restoration of joy in the knowledge of God.
(3) Most frequently the terms so translated mean the giving of spiritual light to the soul (Psalm 19:8; Eph. 1:18, phōtízō; Hebrews 6:4; Hebrews 10:32). This spiritual enlightening the Spirit of God brings about through the Divine word (Psalm 119:130; 2 Tim. 3:15; 2 Peter 1:19). Sin mars the intellectual discernment; “but he that is spiritual discerned all things” (1 Cor. 2:15 King James Version, margin).
The International Standard Bible Encyclopedia.
give (someone) greater knowledge and understanding about a subject or situation:
“Christopher had not enlightened Frances as to their relationship” Merriam-Webster