The effects of illumination level during anodisation on the photoluminescence (PL) properties of n-type porous Si have been studied. The influence of illumination intensity on PL properties is interpreted as a competition between the rate of production of new luminescent material hy anodic etching and the rate of photochemical dissolution of this material. The results are different for heavily doped Si substrates and for n-type polycrystalline silicon films.