The effect of photoinduced conformational transitions between closed and open form of an alkyl-substituted spiropyrane derivative upon the conductance of bilayer lipid membranes (BLM) was investigated. BLM were self-assembled and investigated by the tip-dip patch clamp method from natural soybean lecithin (SoyL) or from synthetic diphytanoyl lecithin (DPhL) mixed with 10% wt hexadecylbenzospiropyrane (SP). Photoisomerization (closed-open) of spiropyrane was effected by repetitive UV light pulses. The reverse isomerization (open-closed) was achieved by continuous illumination with white light. Current vs. voltage measurements were performed in dark, after termination of UV or visible light irradiation. Experimental results with SoyL displayed a reversible increase of the dark BLM conductivity upon UV illumination. However, results with DPhL showed the opposite, although weaker, overal tendency: a visible light-induced increase and a UV-induced decrease. This demonstrated the crucial role of lipid matrix steric asymmetry in the observed photoconductance effects and eventually suggested a different structure of the conducting pores.