My chickens experience extreme temperatures too. -20 with -40 wind chills plus, all in Fahrenheit. Winters are long and hard. No heat lamps here.
Hens will stop laying sometimes after a cold snap. Young birds lay through the winter, though not always steady. There are too many fires from heat lamps. They aren't worth the risk.
From my understanding of providing extra light it needs to mimic daylight as far as it slowly being increased until the 14 hours are reached. Lighting can have negative affects and can cause molts out of season. Done improperly lighting doesn't always work.
This is a slow period for production in most hens. Expect them to increase in early spring as daylight begins to increase. I don't mess with lighting as I think it isn't worth the time and electricity. I have never had a chicken freeze to death either even with a west facing doorway that never closes.