It has been suggested that a NaI(Tl) phosphor be used to amplify densities enough to make a film dosimeter practicable for the low gamma‐ray dose rates produced by background radiation. This use is complicated by the dependence of film density on dose rate as well as dose. An analysis of the process provides a correction for the doserate dependence when the dose rate is constant. The magnitude of the error involved in assuming the dose‐rate constant when it is a function of time is evaluated.