The observable parameters remittance, transmittance and fluorescence emission of layered systems are determined from Monte Carlo simulations and the diffusion approximation. We calculate the effect of additional absorption caused by a fluorescing dye, depending on dye- bearing layer thickness. The results of the simulations are compared to the diffusion approximation, establishing a range of accuracy of the diffusion approximation. We show that, provided the basic optical properties of the system are known, additional absorption and layer thickness can be calculated from non-invasive measurements of remittance and fluorescence emission. We give an estimation of the effect of experimental uncertainty on the results for dye absorption and layer thickness.