The photoluminescence (PL) intensity first increases with anodization time (t a ) and then decreases at very large t a . The increase in PL intensity with t a may be understood if the PL intensity is taken to be proportional to the effective volume of porous silicon (PS) layer under the probe laser beam. The effective volume of PS layer will be proportional to its thickness and reciprocal to the porosity. For a fixed anodization condition, the thickness and porosity both increase with t a . The increase in thickness increases the effective PS volume, while the increase in porosity causes the effective volume to decrease. Therefore, the intensity variation is governed by these two parameters: thickness and porosity. The observed results suggest that the thickness dominates the PL intensity initially and then the porosity becomes more important for very long t a . The PS layers prepared under ambient light illumination also exhibited the similar behaviour. The intensity variation with t a was explained as the interplay of thickness and porosity variations with t a .