A comparative experimental study of bulk and emulsion polymerization of styrene with bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (BAPO) or bis(4-methoxy benzoyl)diethylgermanium (BAG) as photoinitiator or photoinitiator-free reveals astonishing similarities and anticipated differences. Expectedly, both the rate of polymerization and the molecular weight is higher for emulsion than for bulk polymerization. Unexpectedly, the polymerizations continue even if the photoinitiators have been used up and moreover, the average molecular weights increases with monomer conversion. Consideration of all experimental data gives rise to the proposal that the common feature of these polymerizations is photo electron transfer between styrene monomer and a repeating unit in the polystyrene chain.