A model based on Rayleigh-Gans-Debye light-scattering theory has been developed to describe the light transmission properties of fine-grained, fully dense, polycrystalline ceramics consisting of birefringent crystals. This model extends light transmission models based on geometrical optics, which are valid only for coarse-grained microstructures, to smaller crystal sizes. We verify our model by measuring the light transmission properties of fully dense (>99.99%), polycrystalline alpha-Al2O3 (PCA) with mean crystal sizes ranging from 60 to 0.3 mum. The remarkable transparency exhibited by PCA samples with small crystal sizes (<2 mum) is well explained by this model.