The electroluminescence generated during cathodic reduction of peroxydisulfate and hydrogen peroxide at n-type porous silicon electrodes is reconsidered. On the basis of electrochemical results, a mechanism is proposed to account for some unusual features of the reduction reactions and the corresponding light emission. In this mechanism, an extension of a previous model, adsorbed hydrogen plays an important role in both the generation of electroluminescence and the quenching of light emission.