Sounds like you have 220 going to that light. If a 2-pole was used whoever did it probably put the neutral and the hot wire under the breaker. If this is the case the neutral needs to be taken off that breaker and landed on the neutral bar. You only need a single pole breaker.
1-hot(black), 1-neutral(white), 1-ground(green or bare copper) = 110v
This is the reason why you dont let someone wire anything in your house unless you are certain they know what they are doing.