Photon Energy Calculator
Calculate the energy of a photon from its wavelength or frequency.
Shows energy in joules and electron volts, and identifies the spectral region.
A photon is a quantum of electromagnetic radiation. Its energy depends on its frequency (or equivalently, its wavelength):
E = hf = hc/λ
Where:
- E = Photon energy (joules or eV)
- h = Planck’s constant = 6.62607 × 10⁻³⁴ J·s
- f = Frequency (Hz)
- c = Speed of light = 2.998 × 10⁸ m/s
- λ = Wavelength (m)
Unit conversion: 1 eV = 1.602 × 10⁻¹⁹ J
Electromagnetic spectrum reference:
| Region | Wavelength | Energy per photon |
|---|---|---|
| Radio | > 1 m | < 1.24 µeV |
| Microwave | 1 mm – 1 m | 1.24 µeV – 1.24 meV |
| Infrared | 700 nm – 1 mm | 1.24 meV – 1.77 eV |
| Visible (red) | 700 nm | 1.77 eV |
| Visible (violet) | 400 nm | 3.10 eV |
| UV | 10 – 400 nm | 3.1 – 124 eV |
| X-rays | 0.01 – 10 nm | 124 eV – 124 keV |
| Gamma rays | < 0.01 nm | > 124 keV |
The 1240 shortcut
Worth committing to memory if you work with light at all: E in electron volts is roughly 1240 divided by the wavelength in nanometres. Green light at 550 nm gives 1240/550 = 2.25 eV, which is what the calculator above returns. The trick works because hc comes out at 1239.8 eV·nm, near enough to 1240 that the error is under a fifth of a percent. It is quick enough to do in your head, and it is how most people in the field sanity-check a number before trusting it.
The same arithmetic run backwards tells you what wavelength a given energy corresponds to. Silicon has a band gap of 1.12 eV, so 1240/1.12 puts its cutoff at about 1110 nm. Any photon with a longer wavelength than that passes straight through the cell without freeing an electron, and any photon with a shorter one wastes its surplus as heat. Those two losses together are why a single-junction silicon cell cannot get past roughly 29% efficiency, however good the manufacturing gets.
Photon energy is important for:
- Understanding why UV causes sunburn but visible light does not (higher photon energy can break chemical bonds)
- Solar cell design — only photons with enough energy can excite electrons
- Night vision — IR photons carry enough energy to be detected
- X-ray imaging — high-energy photons penetrate tissue
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
SuperGlobalCalculator is independently built and maintained. See how we build and verify our calculators.