In my barns I use metal hallide outside lights because can't buy new mercury vapor fixtures anymore, but they work as well. Like mercury vapor, they take a few to get up to speed, but when they do, they really do. Ones nearer each end, ones in the middle splitting the barns into quarters, they all have their own switches because sometimes I need all of the light, and sometimes I don't. I got the idea from a fella that had kind of poor sight that did it in his barn, and my brother is legally blind and can't see much, especially when its darker. Works good. Very good.