As your attack hits or misses the target, the weapon or ammunition you're using transforms into a lightning bolt. Instead of taking any damage or other effects from the attack, the target takes 4d8Lightning damage on a hit or half as much damage on a miss. Each creature within 10 feet of the target then makes a Dexterity saving throw, taking 2d8Lightning damage on a failed save or half as much damage on a successful one.
The weapon or ammunition then returns to its normal form.
Using a Higher-Level Spell Slot
The damage for both effects of the spell increases by 1d8 for each spell slot level above 3.