(said of fire) bright
烺 centers on the brightness of fire, describing a flame that is vivid and luminous.
烺 combines 火 (fire) with 良, which likely contributes the sound and may reinforce the idea of brightness. The exact historical development is uncertain.
The left side is fire 火, and the right side 良 suggests something good or bright. Picture a good, bright fire blazing warmly.
For コウ, imagine a bright fire that glows like a coal: coal -> コウ, and the fire is bright.