Well two things! I don’t recommend riding in the dark unless in a lit up inside arena. Just because we as riders can’t see all that well in the dark. Horses trust the ride to make the calls, so we could set the horse for failure. And two! Horses don’t have the best vision, they can ofc somewhat see in the dark. But again. Horses aren’t good with depth reception. So to ride a horse in the dark is a very risky thing for horse and rider! I never recommend it, unless you have access to an indoor arena.
I feel like my horse is more focused on me when it's dark, he might be afraid of what is around so he will listen to me and 'trust' me I guess.
Sometimes your horse might be a bit anxious at night, especially if it’s really dark. You just have to be calm yourself, and focus on the task at hand. Hopefully if you’re riding at night you have a lit arena!