Light Is Quantized

Light comes in photons, and each one carries an energy set by its frequency — E = hf. This photon energy calculator plugs your wavelength or frequency into Planck's relation and reports the energy in joules and electron-volts.

Frequency and Wavelength Are One Story

Because every photon travels at c, wavelength and frequency determine each other. Give the calculator either one and it derives the rest: the other value, the energy, and where the photon sits on the spectrum — from gamma rays at femtometer wavelengths to radio waves meters long.

Why Energy Matters

Photon energy decides what light can do: ionize atoms (UV and beyond), trigger photoelectric emission, or just warm a surface. The 2.25 eV of green light and the 4+ eV of near-UV differ by enough to separate a safe tan from DNA damage.