How Does Decreasing Day-length Affect Egg Production?

Egg production can be influenced by many factors, including water and feed quality, housing, space, cleanliness, ect... But even if all those requirements are met and the chickens live in an environment without/lacking in light, they won't lay very many eggs. 

The typical amount of light needed for a hen to be at peak efficiency is right around 15-16 hours of daylight. However, during the fall and winter months, daylight drops a few hours below 15/16 hours of light per day, which is why chickens tend to not lay as many eggs (sometimes none) during the fall and winter months. If you have electricity available in your coops/barns, then you can supplement daylight throughout the winter, but if not, prepare for a drop in egg production. 

I don't have electricity available for my chickens, and one good reason to not have supplemental lighting is that it gives the hen a break from laying, which then enables her to lay eggs over a longer period of time, even if it is a smaller amount per year. 

I have noticed that hybrid chickens tend to lay better throughout the winter without supplemental light, compared to standard heritage breed chickens. Typically, the heritage breed chickens don't lay any eggs during the winter, and then resume laying in the spring, which in the case that you have a flock comprised of a majority of heritage breed chickens, then supplemental lighting would be necessary to keep eggs on your table, or keep your operation afloat during the winter months. 
 

There isn't tons to be said about lighting and it's affect on egg production (at least what can be easily and concisely summarized), unless light duration, intensity, color, and so on is discussed, with which  there have been several studies on different colors and intensities of lights and their affect on egg production.