This is a Channel Divinity option for the Light domain.
As an action, you present your holy symbol, and any magical darkness within 10 meters of you is dispelled. Additionally, each hostile creature within 10 meters of you must make a Fortitude contest. A creature takes radiant damage equal to 1d10 + your divine spellcasting modifier, per point of proficiency bonus on a failed check, and half as much damage on a successful one. A creature that has total cover from you is not affected.