CalcLibrary

Photon Energy Calculator

Convert one known light property into the other two with photon energy shown first in eV and joules. Built for laser labels, spectroscopy lines, UV sources, and optics homework checks.

Examples

A classic germicidal UV-C reference. Start from the wavelength and compare the photon energy in both eV and J.

Photon energy
4.881268 eV · 7.82065 × 10^-19 J
Equivalent wavelength
254 nm · 0.254 um · 2.54 × 10^-7 m
Equivalent frequency
1,180.285268 THz · 1.18029 × 10^15 Hz

Single-photon vacuum relation only. This page does not model refractive-index effects, medium-dependent wavelength shifts, emission-line width, intensity, or material-specific transitions.

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Examples

How It Works

Formula

E=h⋅fE = h \cdot f

E=h⋅cλE = \frac{h \cdot c}{\lambda}

c=λ⋅fc = \lambda \cdot f

Variables

EE

Photon energy(J or eV)

ff

Frequency(Hz)

λ\lambda

Wavelength(m)

hh

Planck constant(J·s)

cc

Speed of light in vacuum(m/s)

Pick the one property you already know, enter its value and unit, and the calculator derives the other two. Photon energy is surfaced first in both eV and J because that is usually the comparison number people actually need when checking UV, visible, and IR sources side by side.

The calculator treats the input as a single-photon vacuum relation. It first converts your chosen unit into a canonical SI value, then derives the other properties from the exact constants below.

  • Planck constant: h = 6.62607015 × 10^-34 J·s
  • Speed of light in vacuum: c = 299792458 m/s
  • Electron-volt conversion: 1 eV = 1.602176634 × 10^-19 J

From wavelength it computes frequency with c = lambda·f, then energy with E = h·f. From frequency it computes wavelength with lambda = c / f, then energy with E = h·f. From photon energy it converts through joules, solves f = E / h, and then lambda = c / f. This is a clean optics utility for comparison work, not a beam simulator or a material-response model.

Frequently Asked Questions

01What relation does this calculator use?
It uses the standard single-photon vacuum relations E = h·f, E = h·c/lambda, and c = lambda·f with exact SI definitions for h, c, and the eV-to-joule conversion.
02Why does the page say vacuum relation only?
Because the calculator converts one idealized photon property into the other two in vacuum. It does not model refractive-index effects, wavelength changes inside a material, line width, beam intensity, or source-specific emission behavior.
03Why show both eV and J?
Optics and spectroscopy work often quote photon energy in eV, while equations and detector notes may use joules. Seeing both at once saves a second conversion step and makes cross-checking easier.
04How is this different from Beer-Lambert, Snell’s law, or an energy converter?
Beer-Lambert is for absorption through a path length, Snell’s law is for refraction between media, and Energy Converter only changes units on a known energy amount. This page derives the wavelength-frequency-energy relationship itself.
05Does it tell me color, intensity, or whether a material absorbs the light?
No. Those questions depend on spectrum width, power, geometry, material data, and source behavior that this calculator intentionally does not pretend to model.

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