Photon Energy Calculator

The photon energy calculator computes the energy of a single photon from its wavelength or frequency.

Photon energy2.254258 eV3.612e-19 J

Wavelength550 nm550 nm — visible, around green

Frequency545.0772 THz545.077196 THz

Wavenumber18,181.8182 cm⁻¹the spectroscopist's unit — proportional to energy, which is why infrared spectra use it

Energy in kJ per mole217.5028 kJ/mola mole of these photons — comparable with bond energies, which run 150 to 1000 kJ/mol

Momentum1.205e-27 kg·m/sE/c — a photon has momentum despite having no mass, which is how solar sails work

Ejects an electron from caesium?yes, with 0.1543 eV to sparework function 2.1 eV — and it is the photon ENERGY that decides, not the intensity

Ejects an electron from sodium?nowork function 2.3 eV — and it is the photon ENERGY that decides, not the intensity

Ejects an electron from zinc?nowork function 4.3 eV — and it is the photon ENERGY that decides, not the intensity

Ejects an electron from platinum?nowork function 5.6 eV — and it is the photon ENERGY that decides, not the intensity

The formula

E = hf = hc ÷ λ; wavenumber = 1 ÷ λ

Energy per photon, not per beam

A photon's energy depends only on its frequency: E = hf, or equivalently hc/λ. Short wavelengths carry more energy per photon, which is why ultraviolet damages skin and infrared merely warms it — and why the brightness of a red lamp is irrelevant to whether it can cause sunburn.

That distinction is the whole content of the photoelectric effect. Whether an electron is ejected depends on the energy of each individual photon against the metal's work function; a very intense beam of low-energy photons ejects nothing at all, while a faint beam above the threshold works immediately. Classical wave theory predicts the opposite, and the failure is what established that light is quantised.

Visible light spans roughly 1.8 to 3.3 eV, which is the same order as chemical bond energies — not a coincidence, since that is exactly why molecules absorb visible light and why photosynthesis and vision are possible.

Photons carry momentum E/c despite being massless. It is tiny, but real and cumulative: solar radiation pressure perturbs spacecraft trajectories measurably and is the basis of solar sails.