arrow of the sun

You touch an arrows or bolt. When a target is hit by a ranged weapon attack using this piece of ammunition the target takes 8d6 radiant sunlight damage. All creatures within a 20' radius of the point of impact,(but not the intended target) can make a dexterity save for half damage.  The flash of light created by impact is treated as actual sunlight for undead.  The spell's magic ends on a piece of ammunition when it hits or misses. 

At Higher Levels. When you cast this spell using a spell slot of 4th level or higher, the number of pieces of ammunition you can affect with this spell increases by one for each slot level above 3rd.