Uskius' Flash of Brilliance

With a critical arcane insight, you amplify a blast of light magic at just the right place and time. Target one creature in range with a ranged spell attack, which can critically strike on a roll of 20-spellcasting ability modifier: on a hit, the target takes 4d4+spellcasting ability modifier radiant damage.

If cast above 3rd level, for each spell slot expended above level 3, increase the class of the damage die by one size on a critical strike.