Porous silicon (PS) presents interesting phenomena such as efficient luminescence and a peculiar transport of carriers. Due to its possible optoelectronic applications, it is important to calculate the dielectric function from interband optical transitions in PS to include quantum effects. In this work, we apply a supercell model for PS within an sp(3)s* tight-binding technique, to analyze the effects of pores on the above-mentioned transitions. The polarized light absorption is studied by observing the oscillator strength behavior within two different schemes, which are applied and compared. We have found a significant enlargement of the optically active zone in the k-space, due to the localization of the wave function. The calculated dielectric functions for crystalline silicon and PS are compared with experimental results, giving the correct energy range and shape.