In order to find a methodology that is a compromise between favorable computational scaling and tolerable errors, a series of nonrelativistic approaches for the calculation of radiative phosphorescence lifetimes are benchmarked against fully relativistic four-component results. The study of the a 3A2-X 1A1 transition intensity in the series of H2CX molecules, where X is a chalcogene atom, X={O,S,Se,Te}, indicates a general good agreement between fully relativistic four-component and nonrelativistic perturbation-theoretical calculations. Among the nonrelativistic approaches, the scaled-charge spin-orbit operator approach is recognized as to provide transition matrix elements that are in good agreement with those obtained with the more elaborate Breit-Pauli and atomic mean field spin-orbit operators. This finding supports phosphorescence calculations using the available linear scaling technology for large complexes and, together with effective-core potentials, large complexes including heavy elements.