In this paper, Re study the effect of optical interference on the emission from conjugated polymer devices. We extend the current models to include the effects of birefringence in the polymer layers. We also include the effect of the variation of radiative and nan-radiative rate with position on the quantum efficiency of emission of an excited state. We then model the overall angular distribution, spectrum and efficiency of emission from a device structure. Experimental measurements of photoluminescence emission from PPV light-emitting diode structures are obtained. Comparison between the experimental and calculated angular distribution of emission is made, and good agreement is found. This demonstrates the importance of birefringence in determining the emission from polymer devices. We also demonstrate how to use the interference model to deduce the position of the recombination zone in electroluminescent devices.