Photon Energy Calculator
Find a photon's energy from its wavelength or frequency.
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How it works
Light comes in discrete packets called photons, and this calculator finds the energy of a single photon from either its wavelength or its frequency. You enter a wavelength in nanometres or a frequency in hertz, choose which, and it returns the photon's energy in both joules and electronvolts. The energy is given by Planck's relation, energy equals Planck's constant times frequency, which can be rewritten in terms of wavelength since frequency and wavelength are linked by the speed of light. The crucial consequence is that shorter-wavelength, higher-frequency light carries more energy per photon: ultraviolet and X-ray photons are energetic enough to damage cells and ionise atoms, while infrared and radio photons are gentle. Visible light photons carry a few electronvolts each, which is why electronvolts are the natural unit here. This quantisation of light energy is a cornerstone of quantum physics and explains the photoelectric effect, atomic spectra, how solar cells and photosynthesis capture light, and why some radiation is dangerous and other kinds are harmless. Chemists, physicists, and engineers working with lasers, spectroscopy, and photonics use it routinely. Because visible wavelengths are hundreds of nanometres, the calculator accepts wavelength in nanometres. Enter a wavelength or frequency to compute the photon energy.
E = h · f = h · c / λ
A photon's energy equals Planck's constant times its frequency. Since frequency equals the speed of light divided by wavelength, the energy can also be written as Planck's constant times the speed of light divided by the wavelength. Shorter wavelengths and higher frequencies therefore carry more energy. Dividing the energy in joules by the charge of an electron converts it to the convenient unit of electronvolts.
Source:Quantum physics (Planck relation)
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How to use this calculator
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Enter your values
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Adjust the options
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Frequently asked questions
What is photon energy?
Photon energy is the energy carried by a single quantum of light. It is proportional to the light's frequency through Planck's constant, so higher-frequency light carries more energy per photon. Photon energy explains why light behaves as discrete packets rather than a continuous stream, a central idea of quantum mechanics that underlies much of modern physics and chemistry.
How does wavelength affect photon energy?
Photon energy is inversely proportional to wavelength: the shorter the wavelength, the higher the energy. So violet light carries more energy than red light, and ultraviolet, X-rays, and gamma rays carry far more, enough to ionise atoms and damage tissue. Longer-wavelength infrared, microwave, and radio photons carry much less energy and are generally harmless.
What is an electronvolt?
An electronvolt is a small unit of energy equal to the energy an electron gains moving through a one-volt potential difference, about 1.602 times ten to the minus nineteen joules. It is convenient for photons and atomic-scale energies because their energies in joules are tiny and awkward. Visible light photons carry roughly 1.6 to 3.3 electronvolts each.
What is Planck's constant?
Planck's constant is a fundamental constant of nature, about 6.626 times ten to the minus thirty-four joule-seconds, that relates a photon's energy to its frequency. It sets the scale of quantum effects. Its small size is why quantum behaviour is only noticeable for tiny particles and high frequencies, and it appears throughout quantum mechanics.
Why does high-energy light damage cells?
Photons with enough energy, such as ultraviolet, X-rays, and gamma rays, can break chemical bonds and knock electrons out of atoms, a process called ionisation. This can damage DNA and other molecules in living cells, causing burns, mutations, or cancer. Lower-energy photons like visible and infrared light lack the energy to ionise, which is why they are far less harmful.