Volatile Radiance

Transparent, shining armor shimmers into existence, floating over your torso. For the duration of this spell bright light radiates from you in a 20-foot radius, with dim light for an additional 20 feet, and you gain +4 to your Armor Class until you take damage.

When you take damage, the spell ends, and the illusionary armor explodes into brilliant radiant energy. Each other creature within a 15-foot-radius sphere centered on you must make a Dexterity saving throw. A target takes 3d12 Radiant damage on a failed save, or half as much on a successful one.

At Higher Levels. When you cast this spell using a spell slot of 4th level or higher, the damage increases by 1d12 for each slot level above 3rd.