I also have an artificial light on my chickens over the winter, and even despite that they still slow down. They haven't entirely stopped yet, but I'm only getting about 2-4 eggs per day out of 17 hens, and most of those are a year or less old. Some factors that contribute to the slow down could be molting (entirely normal) or colder temperatures. They're putting more energy into keeping themselves warm and less into egg laying. If I have a few days of warmer, upper 20s temps I might get between 8-12 eggs. If your chickens aren't getting as much time outside (mine certainly are not because they are weenies and don't like snow), they may get a bit stressed out and stop laying, too. I try to find "activities" for them to do inside the coop, like peck at whole vegetables to relieve some of the boredom, but there's only so much you can do.
Also consider your birds are no longer young. Many chickens only really have an egg laying period of 2-3 years, especially those hybrids like ISA Browns. They churn out eggs, but their laying period and lives are relatively short. Heritage breeds often lay longer, but they won't lay you eggs every day anymore, and instead might give you 1-2 per week. I have a few heritage breeds who are at or over 3 years old and no longer lay eggs for me every day...now they're just pest control haha. I like to have a wide range of ages in my flock so I'm always in eggs, but I appreciate the wisdom the older hens impart on my younger flock members. They free range most days in the summer, and the older hens definitely seem to teach the young pullets about watching out for hawks and other predators, and where the good foraging spots are.
It might be time to consider adding some youngsters to your flock, as your current flock is probably reaching the end of their laying period, anyway. You might consider looking into breeds that are known for laying through the winter. The only other advice I can offer is make sure they always have plenty of fresh water and a decent layer feed to help egg production.