Vampires, eh? Have they considered dropping a Daylight spell and grappling the bloodsuckers?
60 foot radius, plus 60 more of dim light for one hour without concentration. 20 radiant damage at the start of the vampires' turns, disadvantage on attack rolls and ability checks, prevents Regeneration, Shapechanger, and Misty Escape. No saving throw bypasses Legendary Resistance. With disadvantage on ability checks it shouldn't be too hard to grapple them until they crumble to dust, and with disadvantage on attack rolls there is less chance that anyone will get horribly maimed.