That was too flippant and really I'm just trying to get thoughts turned towards the light. A good diet of sufficient protein (not too much) and everything else will only go so far.
I'm learning that chickens develop more sensitivity to light as their day goes on. Of course, if the day only goes 8 hours - there's little sunlight for them to be sensitive to for very long.
Lighting has been studied exhaustively by the poultry scientists. Most commercial outfits don't have housing with natural light. One reason is to control heat loss during the Winter but controlling egg production is their biggest concern.
As I said, the chicken becomes more sensitive to light as the day continues. Apparently, even their combs and wattles are responding to light. After about 11 hours, their bodies are producing the necessary hormones to put them into an egg laying mood.
If their day doesn't have 11 hours of light, they aren't going to be stimulated very much, the researchers have found. At 8 hours of light, any interest in laying eggs may be shut down, completely.
There is virtually no part of the US that has 11 hours between sunrise and sunset on December 21st. So, full-on sensitivity is never reached on that day without artificial lighting. Where I live - - 9 hours of sunlight is still a few days away. I doubt if I'd be getting any eggs at all for another month or so without a coop light bulb.
Steve