Yes good idea of a dim light. We have some that we might be able to rig up. Initially they just had the house and the run, and they didn't want to go out much. Then they all perched, as presumably since they were in the hen house all the time, they could see when it was getting dark. Now they are free range. It seems to me that by the time they decide it's time to go to bed, it's quite dark in the hen house for perching. Getting them inside at 3 ish and leaving the roof vent open (temporarily as it's just for hot weather really) to give extra light, is definitely helping. 3 out of 4 perched yesterday, whereas if they all go in by themselves, they often all sit on the floor.
Best wishes,
Jane