bright, glorious, splendid, flame
燁 centers on intense, radiant light: something bright, glorious, or splendid, often associated with flames or a brilliant glow.
燁 combines 火 (fire) with 華, which likely contributes both sound and the idea of brilliance or splendor. The exact historical development is uncertain, but the fire component clearly points to brightness or flame.
Fire 火 beside 華 (splendor) creates a scene of a glorious, bright flame. Imagine a splendid firework display lighting up the night.
For ヨウ, picture a glorious, bright flame that glows like the sun: 陽 (よう, sunshine) -> ヨウ, and the fire 火 shines with splendor.