There is no sunrise at the Arctic Circle on December 21st.
Anchorage would have 5 hours and 30 minutes between sunrise and set on that day.
Even where I live near the US/Canadian border, the birds will have a 16 hour night. You could probably add another hour of twilight morning and evening...
Commercial outfits keep their houses at 70°. Partly, that must have to do with feed conversion to eggs. The birds will eat more at cooler temperatures and profits will go down.
Light may have more to do with Winter egg production than temperature as long as it doesn't get too cold. I'm happy to...