I use a low watt incandescent bulb on a two stage temp controller. I run the heat cycle about two degrees lower than the cooling cycle and have a 1 degree diff. set on top of that. When I had a single stage controller, I went about 4 months with leaving the light on and letting the chest freezer fight it. This was inefficient of course and let to a good deal of condensation in the freezer. I ferment in a SS corny keg so no worries about light although I'm told that incandescent bulbs are not a worry.