The effect of light on properties of PbTiO3/SrTiO3 superlattices is studied using first-principles calculations in their paraelectric phase p as well as in the, c, r and aa phases that are defined by polarization lying along [001], [11v] and [110] directions, respectively. Whilst the r phase is the ground state in dark conditions, illumination triggers a rotation of the polarization towards the outof-plane direction, which results in the r phase transforming into a c phase at large concentration of photoexcited carriers. We further reveal that a space charge region of free carriers builds up at the interface under illumination, implying that these superlattices can be thought as acting as p-in junctions under light. These free charges screen the polarization discontinuity at the interface, effectively reducing the electrostatic depolarizing field.