Since I live in Northern Lower Michigan, we get lots of cloudy weather in winter (besides snow). My growing area right now is a large "box bay" window with an insulated double casement glazing. I am using two 55 watt CF bulbs near windows and a smaller CF in a reflector for the shade-loving orchids. The lights are on a timer set to 12 on and 12 off. The small fan 24 hours a day to provide gentle ventilation and to be sure orchid posts are dry when night comes.