Visible light emission is obtained during anodic oxidation of heavily doped p-type (P+) porous silicon layers. Similar characteristics are observed for the electroluminescence (EL) on lightly doped substrates (P-). This indicates that the coarser structure of the heavily doped samples also presents a thin structure, with crystallites of quantum sizes responsible for the emission. For the first time the EL and photoluminescence phenomena of this type of material are studied as a function of the oxidation level. So it is possible to separate the passivation effect due to the oxide growth and the carrier injection process into the crystallites. The main characteristics of the light emission are discussed with a simple model which underlines the key role of the injection of carriers (for the EL) and its significance for the oxidation process. The vanishing of the EL, which is observed under anodic oxidation, seems to be related in the higher anodizing potential to some depassivation of the porous silicon surface.