There's a photograph I want to take at dusk that will need artificial lighting and I want to use continuous lighting. There is a local rental house that provides lighting for the film industry and the fresnel lights I'd like to rent have specs of X foot candles at 20 ft. How can I determine how many fc's I'll need for a given f-stop? Let's say f45. Would like to keep the shutter speed above a second, higher if possible. The lighting choices are 10K, 5K, 2K, and 1K. Is there some simple math for this problem? My head is spinning with foot candles, lumens, EV values, etc. but I want to make sure I get the math right.