Armor Of Lightning

You vibrate your own arcane energy, and a protective aura of lightning surrounds you until the spell ends. The target's base AC becomes 15+ its Dexterity modifier. The spell ends if the caster dons armor or is dismissed as an action. The speed of the caster is increased by 20ft. Additionally Any creature with a 5ft cube must succeed on a Dexterity Save. If failed, the creature will take 4d6 of Lightning Damage. If Met the creature takes Half damage. The spell can be cast at higher levels.  The Lightning damage nor speed are increased. Instead the the range of the cube is increased by 5ft per spell level