Scale the sconce to what it sits beside. Flanking a mirror or headboard, the fixture should be about one quarter to one third of that object's height — most fall between 10 and 16 inches tall. Projection matters as much as height: in a hallway or beside a door, keep the fixture within 4 to 5 inches of the wall so nobody catches a shoulder on it, while a living room wall can carry 6 to 8 inches of projection. Beside a bed, mount the sconce 20 to 24 inches above the mattress top.