Sintered porous silicon films contain light scattering voids that enhance the optical absorption. We present an analytical model that coherently calculates the optical absorption, transmission, and reflection spectra in films containing voids with a given size distribution. The main constituents of the model are coherent light propagation of non-scattered light, Mie scattering at the spherical voids, and Lambertian light trapping of the scattered light. The model does not contain any free parameters for fitting the experimental results. For an experimental verification of this model we fabricate 1-to 4-mum thick free standing films of sintered porous Si. Simulated and experimental spectra agree to better than 0.1 in the spectral range from 250 to 1500 nm. (C) 2003 Elsevier B.V. All rights reserved.