The SMPTE standard (196M) is for 16 ftLamberts (as David says) but the tolrance is a little looser - screen centre can vary between 12 ftL and 22 ftL, with edges not less than 75% of the centre reading (and in no case less than 10 ftL).
well out here in india the centre measure's at most 7-8 ft lm and the sides about 5.and i'm talking about the previe screen of the most widely used lab.
how does one compansate for this while shooting?