The systematic change in the shape of the photoluminescence (PL) spectra with the change in the growth parameters for self-supporting porous silicon (PS) and PS layer on Si substrate has been observed and mathematically analysed. The PL behaviour is attributed to quantum size effect and change in concentration of quantum dots and wires. It is found that self-supporting PS layers consists of columns only. For PS layers grown on Si substrate, the concentration of dots was found to increase with a decrease in the concentration of the electrolyte. The mean diameter of the crystallites ranged from 20-30 Angstrom and hence the variation in the confinement energy was from 0.55 to 0.95 eV. The confinement energy for the self-supporting PS was more than that for PS on Si substrate. The variance of the mean diameter of the Si crystallites formed during anodisation, is calculated separately for self-supporting PS and PS on Si substrate.