Some deep litter of straw or hay helps make it warmer. I added straw and hay when this horrible weather came in. I don't use a light with the "deep litter method", I am afraid of fire. It has been told here on BYC that a light left on with straw or hay can become a fire hazard. So of course we don't want that to happen. I feed my 9 month olds, oatmeal (just what I think they will eat at one time), spaghetti plain, they think its worms and they will devour the whole batch. Spaghetti is carbs and it helps bring their body temp up. I give them some ground hamburger, cooked and cooled, protein. Again, it disappears quickly. Yes, the use of a temp light is fine when the cold is extreme. If you don't want to force them to lay more eggs, then I would turn the light out. They are tougher than we are. Sounds like you are doing everything right for where you are located. It will get warmer soon we hope.