14 hours of daylight each day, according to studies, is excellent for egg production. Accordingly, depending on your latitude, when the days are very short in the winter, you might need to add an extra 4+ hours of light to truly see a difference in the quantity of eggs your chickens are producing. A single candle's worth of light has been found in studies to boost winter laying. Even a 4 watt nightlight would probably function! A solar-powered coop light or battery-operated tap-light may serve to reduce the risk of a chicken coop fire caused by electrical cabling. A low-wattage LED light is another option that works nicely.
However, only add lighting to your coop in the morning. It doesn't make sense to add light in the evening since under normal conditions (with natural light), the light decreases gradually as the sun sets, giving your flock time to settle down and get ready for bed. Down contrast, when an artificial light goes off, it happens suddenly, depriving them of the chance to settle in and establish their usual spots on the roost. When the lights go out, they may be eating or drinking on the floor of the coop. Unable to see clearly how to climb back up to the roost, they may run into one another or struggle to leap up in the dark. Therefore, if you want to increase light, just do it in the morning. As the sun sets in the evening, let the light gradually dim naturally.
If you want to produce more eggs, you might also need to install a warmer. You might not see the rise in egg production you're hoping for if temps are frequently below freezing since an abnormally large part of the feed your chickens are eating is being utilized to keep them warm.
Also think about not lighting your coop at all. Constant daylight hours have the drawback of perhaps causing your birds to molt late in the winter, when it is cold and they are most in need of their feathers. Chickens will molt every year regardless of the lighting conditions, but often the shift in daylight is what causes it (not temperature changes). If your hens don't experience the trigger of dwindling daylight hours, they could resist molting for a number of months until ultimately doing so when it is actually too cold to be without feathers.
In conclusion, if you must add light to your coop throughout the winter, wait to do so until after your birds have gone through their yearly molt, and then only add it in the morning.
