photon energy

The term photon energy is used for the energy carried by a single photon of electromagnetic radiation (EMR). A particular photon's energy is directly related to its wave frequency, i.e., the photon is part of an EMR wave such that:

E = h × f

• E - energy of a single photon of the wave.
• h - Planck constant.
• f - wave's frequency.

A typical unit of measurement is the electron volt (eV). For short-wavelength, high-frequency EMR (gamma rays, X-rays, and often the shorter-wavelength portion of ultraviolet), the photon energy (in eV) is generally used to describe the EMR, whereas wavelength or frequency is more often used for longer-wavelength EMR.