Benny's Burning Jacket

You touch a willing creature who isn't wearing armor, and a jacket of magical fire surrounds it until the spell ends. The target's base AC becomes 13 + its Dexterity modifier. The spell ends if the target dons armor or if you dismiss the spell as an action. Whilst the creature is donning the jacket they emit a 10ft radius of bright light and a further 30ft radius of dim light. When a creature targets the creature wearing the jacket with a melee attack, the wearer may use their reaction to force the creature to make a DC13 Dexterity Save and suffer 1D6 Fire Damage. On a successful save the attacking creature takes half damage.