Step 1: Understanding the Concept:
"Radiant" means shining or emitting light, or showing great happiness.
Step 2: Detailed Explanation:
The primary meaning of "radiant" relates to brightness and light. "Bright" is the closest synonym. "Beautiful" is related to appearance but not specifically to light. "Plight" means a difficult situation (opposite meaning). "Influential" means having power to affect others, which is not synonymous.
Step 3: Final Answer:
Thus, "Bright" best expresses the meaning of "Radiant."