Lights will work anyway, no matter where we put them, but for best results with a large mass as a horse is, you want lights coming at it from the side, if you are building new or remodeling.
If someone has the lights already there, they will be fine where they are.
Ours were above the stall walls and illuminated both the aisle and stalls.
Then we moved the stalls back, so now they are over the middle of the twice as wide aisle, it is what it is.
We may say a horse is like a table.
A light right over it will be great to see clearly all that is on top of the table, but you won’t see very clearly what is under the table.
Similar with a horse, lights right above a horse, you will see the top of the horse very well, but underneath there will be shadows.
Light coming from the side will let you see that one side from the top to the bottom, legs included, which we generally want to see in a horse.
We also have some LEDs overhead dusk to dawn lights outside where we walk in and out of barns.
We have two on the front of the barn, three on the side the stalls open into their pens and that lets us check out there also when is dark.
Inside the barn itself we keep it dark if we are not there, but you can see a bit in there from the outside lights, is not totally dark.