Photon Energy Calculator

A photon is the quantum (particle) of electromagnetic radiation. Unlike classical waves, photons carry discrete packets of energy given by E = hf, where h is Planck's constant (6.62607015 × 10⁻³⁴ J·s, exact per SI 2019) and f is the frequency in hertz. Because c = lambda × f for EM waves, this can also be written E = hc/lambda. Higher frequency (shorter wavelength) means more energy per photon: gamma-ray photons carry millions of times more energy than radio photons.

Planck's constant h = 6.62607015 × 10⁻³⁴ J·s is one of the fundamental constants of nature, set exactly since the 2019 SI redefinition. It quantifies the relationship between a photon's energy and its frequency and underlies all of quantum mechanics. Max Planck introduced it in 1900 to explain the spectrum of blackbody radiation, which classical physics could not. Without h, there would be no quantum theory, no atomic structure, no chemistry as we know it, no semiconductors, and no lasers.

An electron-volt (eV) is the energy gained by one electron when accelerated through a potential difference of 1 volt. 1 eV = 1.602176634 × 10⁻¹⁹ J (exact). Joules are extremely large compared to the energies of individual photons and electrons, so eV is a more convenient unit in atomic and optical physics. Visible light photons have energies of roughly 1.77 to 3.26 eV. X-ray photons carry 100 eV to 100 keV. Gamma-ray photons exceed 100 keV.

The photoelectric effect is the emission of electrons from a metal surface when light above a threshold frequency strikes it. Einstein explained in 1905 (earning a Nobel Prize) that light behaves as photons, each carrying energy E = hf. If a photon's energy exceeds the work function of the metal (the binding energy of surface electrons), the excess energy becomes kinetic energy of the ejected electron. This was direct evidence for the particle nature of light and for quantised energy. The photoelectric effect is the operating principle behind photovoltaic solar cells and photodetectors.

Energy increases with frequency (or equivalently, as wavelength decreases). Gamma-ray photons have the highest energies, with wavelengths shorter than 0.01 nm and energies above 100 keV, up to tens of GeV in cosmic-ray gamma rays. X-ray photons follow (0.01 nm to 10 nm, 100 eV to 100 keV). Ultraviolet photons carry 3.1 to 124 eV. Visible light photons carry 1.77 to 3.26 eV. Infrared and radio photons have the least energy. Cosmic high-energy gamma rays can reach energies of 10¹² eV (1 TeV), far beyond anything achievable in a particle accelerator.