Don't know if this helps or not, but here is a link from
Philips for lighting software an another one by
Simkar. Did you obtain a lighting plan that showed the contours of the lighting intensity? It should have been part of the plan package.
"Calculating" candlepower I imagine uses a pretty common equation/practice. However, it seems like your problem was with the contract language. Who told who how much light and to use what protocol/spec. There most likely is going to be a minimum light requirement for any type of facility. However, I would imagine anything above and beyond that would have to be decided between the designer and the client. Find your paper trail. If there is none and no "standard" specification or guideline to follow you are screwed. It would be a change order.