This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
炛 is a rare character. It visually combines 火 (fire) and 化 (change), but its exact historical origin and original meaning are uncertain.
With fire 火 above change 化, picture a fire transforming something into light, like a torch illuminating the darkness. This may help remember the reading て.らす (to shine), but the standalone meaning is unclear.
For ヨウ, imagine a fire 火 changing 化 into a glowing, yodeling flame: yodel -> ヨウ, as the fire shines brightly.