if in a field I think it depends a bit on your surrounding area, our field is surrounded by houses so there is sufficient light pollution that it isn't pitch black, I would suggest you try it and see as your eyes adjust, and presuming it is your field and you know it and the grounding well it is less of a problem. (if not I would go with the headtorch option!)
We do have a large flood light off the stables but I actually find it easier without as it blinds you when going towards it.
Sam I do hack out in the dark (well very first light in the mornings) but I think it is very dependent on where you live/off road options etc. fwiw we have a lot of gear on plus head lamp and rear red lights.
I have been schooling in the dark since a few weeks before the clocks changed as the floodlights have only just been fixed and haven't had a problem. As others have said, there is plenty of light pollution.
I also hack on a busy road. There are street lights and we go out with fluro/reflective jacket, sheet, hatband, neckstrap and boots. I have flashing lights on my hat, arms and legs and pony has a red flashing light on her tail. We go on the grass verge when riding at night to allow more space between us and cars. I drive on this road and have never had a problem seeing even badly lit cyclists - by comparison, pony and I should be seen from space! From there we go onto a dark bridleway which she likes to tank up. Again, there is plenty of light pollution from the road and surrounding houses so I often let her. In several months she has never once tripped or spooked. The way I see it, I turn out at night happily because she can see in the dark - when riding, I expect my horse to see our way and follow the trail and she does this. I do have an experienced sensible pony who I have had for 13 years so we know each other very well. If I had a youngster I might think differently.
We used to go out hacking at night. Not near a road, so no light pollution at all. We knew the tracks well, and our eyes quickly adjusted. Only once had a problem when coming back down towards 'civilisation', there was a late night game at the local sports club, and the floodlights were on. As we came over the top of the hill the light was so bright I was completely blind for at least 100yds. Luckly pony seemed unaffected and brought me home safe. I think any kind of torch/ lamp would have prevented our eyes adjusting and made it much harder.