Photon Mapping

Hi, I'm pretty much new to C++ as kind of feel as if I've been thrown to the wolves with this Photon Mapping assignment. Below is my PhotonMap class so far. My question is, any tips on how to update it to hold a collection of photons?

Code:

class PhotonMap {
   private:
      Scene &scene;
   public:
      // Constructor initializing the reference to the Scene.
      PhotonMap (Scene &sc) : scene(sc) {}
      // compute brightness based on placed photons
      Color illumination (const Point &spot, const Point &normal,
                          double max_dist, unsigned int num_photons) const;
      // randomly place photons
      void trace_photons (void);
      Scene &get_scene (void) { return scene; }
};