1. Yes, the lights in the barn are for you, not the horse!
2. Daylight or lights are triggers for sleep, don't sleep, relaxation, time for breeding, etc. Unless you are trying to trigger a mare out of a normal cycle, probably best to let daylight be daylight, and night be night.
3. Sometimes our idea of a comfortable barn may not be the horses' idea of a comfortable barn. You see this with cattle all the time. They will be down in a dip under some hemlock trees instead of the nice barn you built for them;.)