Photon energy

The photon energy is the energy carried by a single photon with a certain electromagnetic wavelength and frequency. The higher the photon's frequency, the higher its energy. Equally, the longer the photon's wavelength, the lower its energy.

Photon energy is solely a function of the photon's wavelength. Other factors, such as the intensity of the radiation, do not affect photon energy. In other words, two photons of light with the same color (and, therefore, same wavelength) will have the same photon energy, even if one was emitted from a wax candle and the other from the Sun.

The photon energy can be represented by any unit of energy. Among the units commonly used to denote photon energy are the electronvolt (eV) and the joule (as well as its multiples, such as the microjoule). As one joule equals 6.24 × 10¹⁸ eV, the larger units may be more useful in denoting the energy of photons with higher frequency and higher energy, such as gamma rays, as opposed to lower energy photons, such as those in the radiofrequency region of the electromagnetic spectrum.

Photons being massless, the notion of "photon energy" is not related to mass through the equivalence E = mc².

The equation for photon energy is

${\displaystyle E={\frac {hc}{\lambda }}}$

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