I give my chickens 15 hours a day of light. i have a 40 watt bulb in my coop that comes on at 2:30 a.m. to accomplish this. All of my hens are about 7 months old and were laying really well until the day light shortened, then they stopped. i put the bulb in the coop and now i'm back up to about 4 to 7 eggs per day from 10 laying hens. hopefully it will get even better soon.