illumine, light up, reflect
炤 centers on casting light: illuminating something, lighting it up, or making it reflect light so it becomes visible.
炤 combines 火 (fire) with 召, which likely contributes the sound and may suggest calling forth light. The exact historical development is uncertain.
Fire 火 on the left and 召 (call) on the right: imagine calling fire to light up a dark room, making everything reflect its glow.
For ショウ, picture a show lit up by fire: show -> ショウ, and the fire 火 calls forth the light.