A BIG CAVEAT - the darkness is what's keeping the peace in the coop here now. So if you have any coop shenanigans, darkness is best I think.You could experiment. A dim night light might be fine; when in the brooder the chicks here used it, if they fell off their roosts I think it helped them find their way back. But I did dim it down a lot from what it was, the LED was really bright and I taped a piece of paper around the cover and laid a cloth over that.
Last night, in trying to teach the pullets to go in I laid the red light inside the pop door, and it helped draw them in. But they went in and out, dawdling around, and soon Popcorn woke up enough to get annoyed, and she stood up, approached the door and pecked one (probably for disturbing her sleep!). That set everything back and put fear of staying in there into the pullets.
So I doused the light, went around and opened the back, and put them in one by one that way. I stupidly turned on the red light to see better and again they all just wanted to be with me, on me, and definitely outta there away from Popcorn. Popcorn again stood up, no pecking yet but that freaked them out even more and they started trying to scramble up and out the back door.
I doused the light again and just used my hands and arms and voice to try to calm them all down for a bit and I held Popcorn back too, and she sat down again. Then I used the phone app placed on top of the coop to see what was going on. I pushed the door closed but not locked just in case, shut my mouth and was quiet, and let them figure it out. Popcorn tucked her head in her wing, and the pullets ended up in new places. One (Anna I think) had scrambled around the nestbox divider in the panic so was in there with Hazel, who was talking quietly but moved forward a little to accommodate her. Hazel was really pretty nice when one was scrambling around her back even, just some boks. That pullet (Ida Diane I think, because she always wants to be with Anna) ended up perching on the divider between the nestbox and the roost platform facing her friend and Hazel, and the first pullet in there (Anna) snuggled her beak up into Hazel's fluffy butt and leg feathers. The third (Tedi, who often roosts more alone) was near them but on the platform right next to Popcorn. I locked the door and left as quietly as I could.
I don't know how to get them to go in to the coop voluntarily. Suggestions welcome. Tonight just stick them in the back door again, without any fanfare or "training" on where the pop door is, how to go in, etc., like the disaster last night. They'll just start understanding that's where they need to get themselves for the night?
I bet this is why young chickens stay out later - they let it get really dark, so the adults are half-asleep first. That way they don't have to run the pecking gauntlet. It took awhile for Popcorn to bother to do anything about the pullets, she was quietly sitting for most of the pop door "training." This means to me that I need to keep the auto-door timer on the late side to accommodate them.