We investigate the accuracy of an approximate radiative transfer technique that was first proposed by Kylafis & Bahcall ( hereafter the KB approximation ) and has been popular in modelling dusty late-type galaxies . We compare realistic galaxy models calculated with the KB approximation with those of a three-dimensional Monte Carlo radiative transfer code skirt . The skirt code fully takes into account of the contribution of multiple scattering whereas the KB approximation calculates only single scattered intensity and multiple scattering components are approximated . We find that the KB approximation gives fairly accurate results if optically thin , face-on galaxies are considered . However , for highly inclined ( i \gtrsim 85 \degr ) and/or optically thick ( central face-on optical depth \gtrsim 1 ) galaxy models , the approximation can give rise to substantial errors , sometimes , up to \gtrsim 40 \% . Moreover , it is also found that the KB approximation is not always physical , sometimes producing infinite intensities at lines of sight with high optical depth in edge-on galaxy models . There is no ‘ ‘ simple recipe ’ ’ to correct the errors of the KB approximation that is universally applicable to any galaxy models . Therefore , it is recommended that the full radiative transfer calculation be used , even though it ’ s slower than the KB approximation .