David is there a reliable way that you use to calculate roughly what size light units you'd need for particular outdoor scenes.
For instance, let's say you are shooting outdoors in a big field and you obviously know you need HMI's for mediums and closeups, do you at this point just choose units based on experience and by eye? Or do you actually use foot candle/lux calculations to determine how much throw/exposure you'd need at a given distance etc to determine which type of unit you'd need i.e. whether a 6k or 18k or etc.
And do you ever just rely on getting a bigger unit than you'd think you'll need just to be on the safe side?
I remember Roger Deakins said he calculated the foot candles needed etc for the big outdoor night mosco light set up in No Country For Old Men, but I wonder if that's just a special circumstance because that was such an ambitiously grand/rare shot to light, and whether most DP's just order units based on instinct for such circumstances or do you actually look up photometrics of a unit and choose based on your calculation of required footcandles at a given distance etc.?