Believe it or not, lighting more than 18 hours a day can depress egg production and cause cannibalism. I have the references in my reply to CountryBoy4.I put a 60 watt fluorescent in my coop. I leave it on 24/7. My 11 hens (they are all less than a year old) have averaged 7-8 eggs a day all winter. I am in north-central Missouri. It gets cold here. Down to 0 some nights. I have 7 RIR, 3 Leghorns and one Australorp.
All living creatures need a dark period to be healthy. My father milks 350 dairy cows 3x a day, and the night shift is all done with the employees wearing headlamps and the lights off in the barns. Cows who get to sleep well give more milk, and hens that get to sleep well produce more eggs.
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