Just as an anecdote - I was lucky enough to work for Englishman, Gil Taylor (DP on Dr. Stranglove and others), on a commercial in Australia. I was a gaffer/chief lighting technician. We shot the commercial during the course of a week inside a big semi-circular roofed harbour side shed used to build aircraft during the second world war. It had no internal supports and all lighting was a hung from trusses in the roof. There was no sun. We had dozens of 10k's (10,000 watt tungsten fresnel lamps) rigged in the roof and one on the floor for fill. They were not easily adjustable and Gill would look at the subject and suggest a stop (usually t 5.6 - 11 if memory serves) without the help of a meter. He would adjust the fill by having my team drag the floor 10k closer or further from the action - again by eye. The focus puller and I had meters, just in case. We used to double check his stop without his knowledge and he was always right. He was very old school and knew his stock (very unforgiving slow colour neg), lenses and light levels inside out. Obviously once lit, the set would not change dramatically in levels but from the outset he set all levels by eye (i.e the positioning and intensity of each lamp in the roof). For what it was worth the rushes (prints of the previous days shoot) were all perfection on a stick. Cheers, sam