A new model for calculating the effects of refraction is introduced. This model was invented independently of the one described by DeMajistre et al. <1995>, but it is shown that the two models are analytically equivalent. However, the numerical implementation of the model introduced here is vastly more economical and efficient than that of the model by DeMajistre et al. This is because the two differential equations solved numerically by DeMajistre et al. have been solved analytically for the new model, prior to the numerical implementation, which reduced them to only one simple expression. The effects of refraction on stratospheric chemistry calculated with this new model are shown to be greatest in the polar lower stratosphere close to the onset and completion of polar night. The main effect is to change the shape of the seasonal cycle of reactive species produced by photolysis such as NO, NO2, OH, HO2, Cl, ClO, Br, and BrO during the onset and completion of polar night.¿ 1997 American Geophysical Union