The mechanism of light-induced reactivation (LIR) of shallow substitutional acceptors in high-purity p-type hydrogenated GaAs has been investigated. Photoluminescence was used to determine the dependence of the rate and extent of this effect on photon energy, illumination intensity, as well as on sample temperature and chemical composition. At a sample temperature of 1.7 K a sharp threshold in the photon energy, Et, has been observed at about 7.5 meV below the bandgap energy of GaAs. This energy corresponds approximately to the onset of acceptorbound exciton absorption in the material. For photon energy E < Et, only a weak reactivation effect is observed. The efficiency of reactivation increases dramatically for E > Et, and for sufficiently large values of (light intensity).(illumination time) product the LIR process saturates. Both the extent of the subthreshold effect and the saturation level that is attainable with E > Et are independent of the photon energy, excitation power and exposure time in the investigated range of these quantities. For E > Et the initial LIR rate depends on the square of the light intensity, indicating a bimolecular reaction in terms of the photo-generated carrier densities. The observed strong dependence of the saturation level on the sample temperature during LIR is found to be consistent with the relative binding energies of different acceptor-hydrogen passivating complexes in GaAs. Based on these results, it is proposed that LIR of acceptors is electronically stimulated via recombination-enhanced vibrational excitation of acceptor-hydrogen complexes.