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.
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Ross
http://orchids-ross.blogspot.com/
I don't do most Dendros or large, "floofy orchids". For me it's minis (like Angraecoides), Masdies, Paphs, and others that crept in somewhere along the line. See my orchid list for complete collection (usually not current.)