The temporal evolution of the spectra of cathodic electroluminescence from porous silicon in an electrolyte containing persulfate ions S2O 8 2− was studied in the galvanostatic mode. It was shown that irreversible changes in luminescence properties of porous silicon occur under cathodic polarization. These changes are manifested in a decrease in the signal intensity and a long-wavelength shift of the electroluminescence (EL) spectrum when the substrate potential remains virtually unchanged (pseudo-tuning). The irreversibility of the change in luminescence parameters is related to a concurrent electrochemical oxidation of the surface of porous silicon, which hinders the bipolar injection of carriers into luminescence-active crystallites. The results obtained suggest that the degradation phenomena observed under cathodic polarization are due to those same processes which are responsible for EL excitation, which casts doubt on the interpretation of the tuning effect, known in the literature, as a consequence of a purely electronic process in porous silicon.