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.
It's cloudy and drab enough here this week that I need room lights on to see. I'm getting from 500 FC at the back (under the small light) to about 1500 near the two big lights. That's enough.
Nice setup and well conditioned for the gloomy days. Been in Chicago during those type of conditions and yep, depending on the cloud cover thickness a lighting effect indoors to see what you need out of a cupboard is a good sign your chids will be thriving for some light.
I've added a third 55watt CF at the back to increase foot candles. My original estimates were probably a bit low. Everything is doing well and many plants in bud or spike.