We study the role of liquid films for light transport in dry foams based on ray optics. The foams are modelled by two-dimensional Voronoi tessellations with varying degree of disorder. We perform extensive simulations to determine the diffusive limit of light for two models. In model I, we choose a constant intensity reflectance r to explore the effect of disorder. We show that the honeycomb structure sets the right order of magnitude for the diffusion constant D by providing a master curve for D(r), whereas disorder reveals itself in a fine structure. In model II, the reflectance for thin films as determined by Fresnel's formulae is chosen as well as some disorder in the film thickness. We argue that this model reproduces experimental features and the right order of magnitude for the diffusion constant. This suggests that the liquids films in combination with ray optics are relevant for explaining photon diffusion in foams.