Photon energy calculator
Photon energy and frequency from wavelength.
Fill in the fields and the result will appear here automatically.
The frequency determines the energy of one photon. Enter its vacuum wavelength in nanometres to obtain joules, electronvolts, frequency and spectroscopic wavenumber. Shorter wavelengths mean more energy per photon: doubling that energy requires halving the wavelength. The calculation concerns a single photon; it has no source power, exposure duration or assessment of effects on people.
How it works
Formula and logic
E = hc/λ, with h = 6.62607015·10⁻³⁴ J·s and c = 299 792 458 m/s.
Example
Green light at 550 nm carries 3.612·10⁻¹⁹ J, that is 2.254 eV.
Fields and units
- Wavelength — nm
How to use
- — Enter a positive vacuum wavelength. A wavelength measured inside a material also requires its refractive index. Multiply nanometres by 10⁻⁹ to obtain metres.
- — Wavelength in nanometres: visible light runs roughly 380–780 nm. For X-rays and gamma radiation use fractions of a nanometre — the calculation holds there too. Electronvolts are handier than joules: visible light is 1.6–3.3 eV. Wavenumber in reciprocal centimetres is the spectroscopist’s unit.
- — The wavenumber here is 1/λ in cm⁻¹, rather than the angular wavenumber k=2π/λ. A positive quantity outside the numerical range produces a range message instead of a physical zero.
Method and limitations
- Calculation method
- Formula and logic
- Data or methodology source
- OpenStax §6.2: single-photon energy and photoelectric threshold NIST CODATA 2022: exact h, c, e and measured ε₀
- Limitation
- The calculation concerns a single photon; it has no source power, exposure duration or assessment of effects on people. Enter a positive vacuum wavelength. A wavelength measured inside a material also requires its refractive index.
FAQ
Why does this result not establish radiation risk?
Energy per photon does not specify the received dose or the consequences of exposure. The calculation has no power, duration, exposed area or tissue/material properties, so an eV value alone cannot establish those effects.
Does photon energy depend on brightness?
No: at fixed frequency each photon has the same energy. Changing the photon flux changes the energy transferred over time. Photoelectric emission depends on frequency and the work function of the particular material; there is no universal red-versus-ultraviolet rule.
What is an electronvolt?
The energy an electron gains crossing one volt: 1.602·10⁻¹⁹ J. In these units photon energies, bond energies and levels come out as numbers of order one rather than powers of ten.
How do energy and frequency relate?
Directly: E = hν. Wavelength and frequency are tied by the speed of light, so any two of the three fix the third.