A Monte Carlo simulation is presented for the transport of mercury 254 nm radiation in the cylindrical positive column of an argon‐mercury fluorescent lamp. Of particular interest are factors influencing the fractionfof photons which, once initially created by electron impact excitation in the volume of the lamp, actually escape to the outer wall of the lamp rather than being lost to nonresonant quenching. Increases infof up to ≊6%, reported earlier from a similar model [Andersonetal., Phys. Rev. A31, 2968 (1985)], are confirmed for artificial increases in the abundance of the196Hg isotope to ≊10%. Other manipulations of the isotopic mercury content are investigated here, but none increasefby more than a few percent. Externally applied axial magnetic fields up to 0.15 T are found to increasefby up to 15%.