Photon energy is the energy carried by a single photon. The massless photon mediates the electromagnetic interaction. Part of the energy of the photon is transferred to the recoiling electron. These particles act as a force particle similar to the photon of the electromagnetic interaction. Radiometry is distinct from quantum techniques such as photon counting. It is defined as the number of signal electrons created per incident photon. Similarly, would correspond to an infrared photon of wavelength or frequency . The wavelength changes as a function of the energy of the incoming photon. It is a form of inelastic light scattering, where a photon excites the sample. The phase and direction associated with the photon that is emitted is random. There is a unique atom in the lattice that interacts and absorbs this photon. Let's assume the crystal lattice absorbs the incoming photon. The chromophore absorbs the photon and undergoes photoisomerization. A partial photon is never experimentally observed. The frequency of a photon is proportional to its energy.