The only light I've ever used was for heat when I had a few month-old chicks in a fairly large brooder coop out back; was concerned that the body heat from only 3 chicks wouldn't be enough for them. Other than that, I'm pretty much of a "let Mother Nature do what she does best" kind of guy. Grown birds, depending on breed, don't need artificial heat to stay healthy, as long as they can get out of drafts & stay dry. The only exception, IMO, would be if there were too few birds to generate sufficient body heat. I have 6 RSL's in a 3'4 insulated coop where temps get down into single digits overnight, and they do just fine. Egg production does go down in the winter when natural light is shortest, but I believe they benefit from the rest, just as in nature.
There you have my 2 cents worth of input; use it or not as you wish.