December's winter solstice (or June's, if you're in the southern hemisphere) sees daylight hours reduced to, at most, 8, from a summer high of between 14 and 17 hours (18 in northern Scotland, UK; 24 hours in northern Alaska!).
In the far north of Scotland it can be as little as 6 hours, in Alaska even less - around 3 to 4 hours.
So how does the declining light affect chickens?
And should we be providing them with additional light during the dark, winter months?
Why have extra light in the coop?
As day length approaches 14 hours per day during early spring, chickens begin laying eggs, gradually increasing their production as the day length increases.
Studies show that they reach their maximum egg laying potential when daylight reaches around 16 hours per day(1). It's a wonder of nature thing.
More light means more eggs means more chicks.
And chicks hatched in the warmer Spring and summer months are more likely to survive than those hatched out in harsh winter weather.
As light decreases naturally, so do a chicken's egg-laying hormones.
Commercial egg producers, and some backyard chicken keepers, add light to coops in dark winter months to keep their hens laying for as long as possible.
This is a long and very detailed article. If you want to jump to a particular section, use these links. Otherwise, carry on reading!
Chickens "see" light differently to humans. They have more sensitive eyes and see light more intensely than we do.
Right above and slightly behind the eye is the pituitary gland. Light enters through a thin part of the hen's skull and stimulates that gland to produce a hormone.
The hormone is carried in the bloodstream to the ovary. In the ovary, it triggers eggs to be produced. Long days of 14+ hours of daylight mean the hormone flow is triggered and maintained. Hens produce an egg a day - or thereabouts.
Less light means no hormone, so no trigger. That's why most hens stop laying once daylight drops to under 14 hours.
It's really that simple.
But not quite.
Because studies have also repeatedly shown that supplying light for more than 17 hours actually decreases egg production(2).
So the optimum daylight time required to encourage hens to lay the optimum number of eggs is between 14 and 16 hours per day.
Studies(2) have shown that the intensity of light does matter in large commercial productions, and should be at least 5.38 lumen, with the optimum being 15lx.(3).
Other studies(3 and 4) suggest that the colour of light is also important: white and red lights stimulate production more than blue or green.
Seriously - blue or green lights? It would be enough to put any chicken off.
In any event, the jury is still out on whether light colour matters. If you're going to add light to a backyard coop, a soft white light closest to daylight is probably the best.
There's no evidence of this in adult hens. You'll see some blog articles saying it decreases the hen's life because she'll become "spent" unless she has a break from laying.
That's not true.
What is true is that a hen is hatched with all her potential eggs already inside her. She can't increase that number. There's no need - it runs into the thousands.
So producing eggs during the winter won't shorten her life, but it may shorten her egg-laying life.
It's a different story for young pullets, though(5). Too much light too soon can cause a young chicken to develop before her body is ready to support egg-laying.
For that reason, it's not recommended to provide artificial light for hens under the age of 16 weeks. 20 weeks is safer still.
Studies(4) have demonstrated that while the number of eggs is increased by artificial light, the quality of the eggs remains the same.
Of course, quality will be affected by the fact that, in the winter, it's harder for chickens to forage for bugs and plants. But light itself does not alter the quality.
Take a look at my egg collection during the summer.
Now take a look at it in winter - the photo below was taken in early December.
I don't provide extra light in my coop. What explains the difference?
The explanation is that all but my Red Stars have stopped laying.
Red Stars, and other commercial chickens, have been bred for many generations to keep producing eggs all year round. My Leghorns do the same. They may slow down a little during moult and in the depths of winter, but they never stop completely.
So if you want a good egg-producer without adding light to the coop, stick with commercial type breeds.
Whether or not you provide light in your chicken coop during the winter is a matter of personal choice. The evidence is that it doesn't physically harm your hens, and may actually help prevent damaging behaviours.
My personal choice is not to add light, because I don't want electricity in my coop.
Instead, like others in rural Italy where I live, I view eggs as a seasonal food. I choose to have a good number of hens I know to be excellent egg-layers for most of the year.
And when they slow down or stop laying, I accept that as their time off work.
Whichever you choose, as long as your decision is based on good quality, accurate, proven facts like those in this article, then it will be exactly the right option for you, your family - and your chickens.
A lot of "facts" you'll find on the internet are often people's individual views, often based on inaccurate information repeated from poor quality sources.
The information I provide in this article and others is based not just on my own experience, but on evidenced facts from scientific, peer-reviewed research and evidence from highly respected and experienced poultry keepers such as Gail Dammerow.
Some of the sources I have used for this article are these.
1. Bayram, A and Ozkan, S: Effects of a 16-hour light, 8-hour dark lighting schedule on behavioral traits and performance in male broiler chickens. Pub. Poultry Science Association, 2010.
2. Ostrander, C and Turner, C.N.: Effect of various intensities of light on egg production of single comb white Leghorn pullets. Pub. Journal of Poultry Science, 1962.
3. Alphin, R: Impact of light on poultry. Pub. University of Delaware,
4. Jacome, I, et al: Influence of artificial lighting on the performance and egg quality of commercial layers: a review. Pub. Brazilian Journal of Poultry Science, 2014.
5. Er, D et al: Effect of monochromastic light on the egg quality of laying hens. Pub. Journal of Applied Poultry research, 2007.