We did it a few years ago when we were on a large yard.
It was Halloween so everyone dressed up themselves and the ponies. We were all in dark colours no hi viz or lights. Virtually the whole yard went, you couldn't see much at all except for when the moon came out. All the kids had to have a mum or dad walk with them. There must have been at least 30 horses + loads of camp followers
It wasn't as dangerous as it sounds as we had lit lorry and walkers in front and behind the herd to stop the traffic until we got off the lane into the fields.
It was brilliant, us and the ponies loved it they couldn't believe it when we started tacking up at 9pm. It was great fun.
In general though I would NEVER ride on the road in the dark in fact not even in the half light it's just too dammed dangerous. I came close to hitting a horse last year. It was a late on a winters afternoon getting dark and also misty and drizzly. The rider did have a tabard but just didn't show up until we were right behind it. Luckily i was only going 30 some people go up this road at 60