Arcane Archer Lightning Arrow

You fire off a shot from your bow that transforms into a bolt of lightning. The stroke of lightning forms a line 100ft long and 5ft wide in a direction you choose starting from your location. Each creature in the line must make a Dexterity saving throw. A creature takes 6d6 lightning damage on a failed save, or half as much damage on a successful one. 

The lightning ignites flammable objects in the area that aren't being worn or carried. 

When you cast this spell using a spell slot of 4th level or higher, the damage increases by 2d6 for each slot level above 3rd.