We have electric to the coop, so we use at 40 watt light bulb in a reflector hood from August 15th until May 15th. I was always told 14 hours is best, so I start when the sunlight goes below 14 hours & start out at 5 a.m. until 8 a.m. (when the sun is up bright on the coop) & gradually turn the timer back each week until December when the sun sets at 4:30 or so, my light would go on about 2:30 a.m. We use a cheap mechanical lamp timer & its has been the same one for years. If you don't have electric in your coop, a heavy duty outdoor extension cord will work, if your coop is not too far away from an electric source. Sunlight times will of course vary by your location. Electric is also convenient for a water warmer of some sort.