Horse Barn

1. Ask the owner what they have seen and is that what they want.
2. T12 are a thing of the past. Don't even consider them. Go to T8 or T5.

What is ceiling height? Is this in the stalls or in a riding arena? Do have a reputable supplier you work with? He/she can help you on lighting design by putting you in contact with the agency who sells the fixtures to them. The agency can do a photometric layout of proposed fixtures.

The only two horse barns I have wired had "hay mow lights" in the stalls. I don't know what you call these lights. They are the one's with a single incandescent lamp, mason jar type glass screwed on, with a wire type gaurd screwed over that. The aisles, feed rooms, and tack rooms had T8's with reflector and tube sleeves, and the riding/show arena had metal halide low bays.

HO found some t-8, 4 tube with a plastic cover that one would put in a kitchen. They are happy with the look. The ceiling is 10', and this is down the center. We are using the same light for the tack room. The stall lights are going to be dual 150 w floods mounted at ceiling height to shine into the stalls.
There will not be an arena.

Whatever they want, but...

Horse barns are full of flies in the summer. Those covers on those fluorescents will be full of dead flies. No special hazard, but possibly a bad call on their part.