Photon Energy From Wavelength Calculator

1) What this calculator does

Photon energy links light’s wavelength to the energy carried by a single photon. This calculator converts your wavelength into energy in joules and electronvolts, and also reports frequency. It supports common wavelength units, so you can work directly in nm for optics or in µm for infrared sensors.

2) The core physics relationship

The computation uses E = h·c / λ, where Planck’s constant is h = 6.62607015×10⁻³⁴ J·s and the speed of light is c = 299,792,458 m/s. Because energy is inversely proportional to wavelength, shorter wavelengths always produce higher photon energies.

3) Converting units correctly

Internally, wavelength is converted to meters before evaluating the equation. For example, 500 nm = 5×10⁻⁷ m. The calculator then converts joules to electronvolts using 1 eV = 1.602176634×10⁻¹⁹ J, which is convenient for spectroscopy and semiconductor work.

4) Typical spectral ranges and energies

Ultraviolet spans roughly 10–400 nm and corresponds to higher energies (several eV and above). Visible light is about 380–750 nm, commonly around ~1.65–3.26 eV. Infrared starts near 700 nm and extends to ~1 mm, typically below ~1.77 eV and often far lower for thermal wavelengths.

5) Quick reference examples

A 400 nm photon is near the violet edge and is about 3.10 eV. A green 532 nm laser photon is about 2.33 eV. A 1064 nm Nd:YAG photon is about 1.17 eV. These ballpark values help you sanity-check lab readings, filter selections, and detector responsivity claims.

6) Frequency output and why it matters

Frequency is computed from f = c / λ. Frequency is useful when comparing radio and microwave specifications or when converting between optical and RF conventions. Since E = h·f, the frequency and energy results are consistent views of the same photon.

7) Precision, rounding, and custom constants

The calculator uses CODATA-exact values for h and e, and an exact value for c. You can enable custom constants for specialized scenarios, but most users should keep defaults for reproducible, comparable results. Output rounding is applied for readability without changing the underlying computation.

8) Where wavelength-to-energy conversions are used

This workflow appears in photochemistry, solar cell bandgap matching, LED and laser selection, Raman and fluorescence analysis, astronomical photometry, and radiometry. Converting wavelength to photon energy helps you compare photons to material bandgaps (eV), reaction thresholds, and detector sensitivity curves, improving design choices and interpretation accuracy.

1) Why does shorter wavelength mean higher energy?

Energy is inversely proportional to wavelength in E = h·c / λ. Halving the wavelength doubles the photon energy, which is why UV photons are more energetic than infrared photons.

2) What units should I use for wavelength?

Use the unit you measure directly: nm for visible/UV, µm for IR, and m for general physics. The calculator converts everything to meters internally, so the result is consistent across units.

3) What is the difference between joules and electronvolts?

Joule is the SI unit of energy. Electronvolt (eV) is a convenient microscopic unit used in atomic, optical, and semiconductor physics. They are related by 1 eV = 1.602176634×10⁻¹⁹ J.

4) Is this valid in air or only in vacuum?

The formula uses the speed of light in vacuum. In air, the wavelength changes slightly due to refractive index, but photon energy depends on frequency, which is largely unchanged. For most practical cases, the vacuum-based result is an excellent approximation.

5) Why do you also show frequency?

Frequency provides an alternate view of the same photon: E = h·f. It helps when specifications are given in Hz, or when comparing energy scales across optical and electromagnetic bands.

6) Can I estimate a material bandgap using wavelength?

Yes. A rough relation is that a photon with energy near the bandgap can be absorbed. Convert the wavelength to eV and compare it to the bandgap value; absorption typically increases once photon energy exceeds it.

7) My result looks off—what should I check?

Verify the wavelength unit, especially nm versus µm. Also confirm you entered wavelength (not frequency) and that custom constants are disabled unless you intend to change them. Finally, compare against a known reference point like 500 nm ≈ 2.48 eV.