Lifetime prediction of polymers requires accelerated ageing based on an increase in UV light intensity and temperature. However, the representativeness of artificial ageing is still an issue. The relevance of highly accelerated UV-induced weathering raises the question of reciprocity failure depending on the polymer. The influences of irradiance and temperature on the photooxidation kinetics of polyethylene were studied to determine the extent to which increasing light intensity leads to accelerated photooxidation of polyethylene. Polyethylene films were subjected to accelerated photooxidative experiments at various UV light intensities and different temperatures, and the amounts of carbonylated photoproducts were monitored by IR spectroscopy. The results show reciprocity failure for polyethylene photooxidation and the limits of acceleration by UV light.