Twilight Flame

You produce low golden flame in a 10ft radius at a chosen area. Anyone within that area must make dc CON save of a 18 or better. On a failed save, targets take 4d6 Fire damage and 1d8 Raidiant damage and have the Prone condition until the start of next round or put out beforehand. If putting out beforehand you may do so as a bonus action as you roll on the gound or pour water on yourself to remove the flames.  On a succes save you do take half damage and not affected by the Prone condition. 
Casting the spell above a 4th level increases the number of dice for each damage by 1. 
If attacked while preparing for the spell you must make a spell save dc in order maintain preparing it. Spell save is equal to your spell save dc plus spells level.