Abstract: Light developed by an implantable probe is used to illuminate a treatment site that has been perfused with a photoreactive agent. A number of different embodiments of implantable probes are disclosed. Preferably, an array of light emitting diodes (LEDs) or solid-state laser diodes (LDs) are mounted on a light bar inside the implantable probe and are energized either using a storage battery power source, an inductively coupled external transformer, or with current provided in leads running through a flexible catheter that extends outside the patient's body to an external source. The implantable probe is normally intended to be disposed inside a patient's body during a surgical procedure, at a treatment site, and left in place for several days (or longer) after an incision is closed, while light produced by the array of LEDs or solid-state LDs irradiates the treatment site.