West or southwest facing windows can help when you are in the western hemisphere. A skylight can be good as well. Another option is a small (stressing small) nightlight that shines light on the ceiling or back wall. A light too bright may also disrupt going to roost resulting in birds eating...
Make certain light levels in coop are not dropping too fast relative to light levels outside. That can happen when sun changes position in sky at sunset with change of seasons. Also check crop fill as birds having trouble filling up for one reason or another will delay going to roost, That...