You might want to consider a light mover, which will move the light to and fro along the 12 feet(3.6M) distance. But i'd also agree with llamaman666.
EverCM Reviewed by EverCM on . 400 watt hds my room is 12 feet long by 4.5 feet wide and 7.5 feet high and have a 400 watt is this enough, it is on a light mover and the walls are painted white Rating: 5