A system and method for light stimulation within a medium. The system has a reduced-voltage x-ray source configured to generate x-rays from a peak applied cathode voltage at or below 105 kVp, and a plurality of energy-emitting particles in the medium which, upon radiation from the x-ray source, radiate at a first lower energy than the x-ray source to interact with at least one photoactivatable agent in the medium. The method introduces the plurality of energy-emitting particles into the medium, radiates the energy-emitting particles in the medium with x-rays generated from a peak applied cathode voltage at or below 105 kVp; and emits a lower energy than the x-ray source to interact with the medium or with at least one photoactivatable agent in the medium.