Porous silicon multilayers are easily produced by a variation of the current density during the electrochemical etching process. The obtained porosity profile in depth is equivalent to a refractive index profile. Preparing appropriate multilayer systems one can design optical filters with sharp reflectivity peaks from the infrared through the whole visible spectral range (dielectric mirrors). Stability in time is achieved applying a suitable oxidation process. In many cases of optical process and material control the required spectral decomposition of the probing light can be done with sufficient accuracy by a set of porous silicon optical filters whose spectral characteristics can lbe adapted easily to the given problem. In this work we present the prototype of an optical sensor that is a low-cost alternative to ‘real’ (and expensive) spectrometers. Application examples in the infrared and visible are given to demonstrate the sensor performance;.