On the basis of input from in situ measurements of key parameters determining optical properties (i.e., snow grain size, density, ice salinity, ice temperature, etc.) we calculate the transmittance of shortwave radiation (280 nm < λ < 800 nm) through first-year sea ice with and without snow cover. We use a multistream radiative transfer code that takes into account the coupling between two strata with different indices of refraction (i.e., the atmosphere-snow stratum and the ice-ocean stratum). Also, we give a detailed description of the parameterization used to calculate the optical properties for shortwave radiation in the atmosphere, snow, ice, and ocean. Through comparisons between calculated and in situ measured transmittances we tune the model to obtain consistency. We find that for the type of snow and ice considered in this study a 2.5-cm-thick layer of snow is less transparent than a 61-cm-thick layer of ice. Also, the diffuse attenuation coefficient for snow Kd varies considerably with the snow thickness, emphasizing the need for accurate radiative transfer modeling. Our model not only provides accurate transmittances but also gives accurate values for ultraviolet and visible light versus depth in the atmosphere, snow, ice, and ocean. This makes it a suitable tool for both calculating energy deposition in icy polar waters and predicting effects on polar aquatic ecology due to changes in the light conditions.