How to Use Photon Energy Calculator
The Photon Energy Calculator converts a wavelength or frequency into the energy of a single photon.
- Choose the input - Wavelength (nm, μm, m, Å) or frequency (THz, GHz, Hz). The Photon Energy Calculator accepts a wide range of sub-units for both input types.
- Optionally set the refractive index - For a photon traveling inside a medium, the frequency stays the same so E is unchanged; the calculator reports the in-medium wavelength λ_n = λ / n for reference.
- Read the result - The Photon Energy Calculator returns J, eV, and kJ/mol simultaneously, so you can use the same result in physics (eV), chemistry (kJ/mol), or engineering (J) contexts.
- Compare different wavelengths - Enter the red (700 nm) and blue (400 nm) ends of the visible spectrum to see the 1.75× energy ratio, illustrating why UV photons are more chemically and biologically active than visible ones.
Formula & Theory - Photon Energy Calculator
The Photon Energy Calculator uses:
E = h · f = h · c / λ
E (kJ/mol) = N_A · E (J) / 1000| Symbol | Meaning |
|---|---|
| h | Planck constant |
| f | Photon frequency |
| λ | Wavelength (vacuum) |
| c | Speed of light in vacuum |
| N_A | Avogadro constant |
Quick Reference Energy Values
| Wavelength | Band | E (eV) | E (kJ/mol) |
|---|---|---|---|
| 700 nm | Red visible | 1.77 | 171 |
| 550 nm | Green visible | 2.25 | 217 |
| 400 nm | Violet visible | 3.10 | 299 |
| 280 nm | UV-B | 4.43 | 427 |
| 1550 nm | Telecom IR | 0.80 | 77 |
Assumptions and Limits
The calculator assumes a single, monochromatic photon in vacuum. For broadband light, integrate the spectrum or compute photon counts per nm/THz interval.
Use Cases for Photon Energy Calculator
The Photon Energy Calculator is useful when you need a quick, transparent calculation for photonics and photochemistry:
- Laser selection - Match photon energy to a target electronic transition (e.g., 532 nm for 2.33 eV transitions in green-laser spectroscopy).
- Solar / band-gap design - Compare photon energies across the solar spectrum with semiconductor band gaps (Si 1.1 eV, GaAs 1.42 eV, perovskite 1.5–1.7 eV).
- Photochemistry - Use kJ/mol output to compare directly with bond dissociation energies and assess whether a photon can drive a desired photochemical reaction.
- Astronomy - Convert spectral-line wavelengths to photon energies for X-ray or UV line identification in stellar and nebular spectra.
- LED and display design - Confirm that the photon energy of each color LED correctly falls within the intended color band of the human visual response.
- Dosimetry - Assess the energy deposited per photon in radiation biology and phototherapy applications (e.g., 365 nm UVA vs 254 nm UVC for DNA damage).
For broadband sources, repeat the conversion at the spectrum edges or integrate the spectral energy distribution. The Photon Energy Calculator delivers exact single-photon energies across the entire EM spectrum.