We are having a cold snap here in Colorado (in the 20's to 30's). I know it can get worse at times, so I had set up the coop with a hook for a light. Currently have just a regular bulb in there. My coop is small (just 16 sq ft, about 4.5 feet tall, with 5 girls) so that is plenty to take off the chill. I am also experimenting to see if it bumps egg production back up, because we went from 4-5 a day to 2 a day. I had read that it can help, and I had read that it may do nothing. I now fear that I have totally thrown the girls off. I went out the back door about an hour ago (3-4 hours after sunset) to let my neighbors dogs out, and the girls all came tumbling down the ramp making their "oh good, here come some goodies" noise. They should be happily roosting right now. So will the light totally keep them thrown off, should I just set it to run through some part of the day, or will they adapt? I know that the heat isn't really needed at this point, but I still haven't sealed as many of the gaps as I had intended with my design. The coop is elevated with part of their run underneath to give them space out of the weather when needed. I had added sides underneath to give them more cold weather shelter, and have added a thicker layer of straw to the bottom of their coop for warmth. thanks for your wisdom, oh great chicken gurus!