We have expanded our studies on illuminated YBa2Cu3Ox grain boundary Josephson junctions (GBJJ) which show both dc Josephson properties (Fraunhofer pattern) and ac Josephson properties (Fiske resonance). Illuminating GBJJs with visible light changes the Josephson coupling. This change is characterized by an increase of the critical current and a large shift in the voltage position of the Fiske resonances. This effect is due to persistent photoinduced superconductivity (PPS) of the oxygen-depleted YBa2Cu3Ox barrier, similar to the PPS found in illuminated oxygen-deficient YBa2Cu3Ox thin films. From Fiske resonance experiments in GBJJs of different lengths, it is possible to study the velocity of the electromagnetic wave in the barrier and its change after illumination. Information on the parameters of the barrier, before and after illumination, is obtained from this study.