Concept: Duke’s pupils glow white when he uses his powers. White rather than gold matches his bat symbol and fits that he’s about light itself, not just sunlight. The pupil glowing represents how his retina, the part which the pupil opens to and actually responds to and absorbs light, would probably be the part affected by his metahuman power to absorb light in superhuman ways; is a somewhat more subtle power indicator than glowing irises; avoids giving yet another black character/PoC unnaturally non-brown eyes, even temporarily; and tell me circles of bright white inside dark brown irises isn’t an immensely cool image. Light in the darkness. Like the classic solid white eyes in Batman’s cowl in some art styles.