Commentaries:
A thing that shines gives light. A shining object reveals itself. This is the psalmist's point. He is asking God to reveal Himself, and he requests it through the symbolism of light or shining. Light cannot be hidden in darkness. When a light shines out, a person immediately sees it, and his eyes are attracted to it. "God, make Your face to shine on us, revealing Yourself, so that I can see You and have direction." Here, light and truth signify the same idea.
John W. Ritenbaugh
Truth (Part 3)