Light doesn't deliver its energy continuously — it arrives in discrete packets called photons, and every photon of a given frequency carries exactly the same amount of energy. This calculator applies the Planck–Einstein relation, E = hf = hc/λ, to convert any wavelength or frequency into photon energy, in both joules and the more convenient electronvolt scale.
How the Photon Energy Calculator works
The calculator implements the Planck–Einstein relation E = hf, where h is Planck's constant. Because the speed of light c relates wavelength and frequency by c = λf, the same energy can equally be written E = hc/λ. Enter a wavelength on the Energy tab or a frequency on the From Frequency tab, and the calculator solves whichever form applies, then cross-derives the other quantity so both are always shown.
All calculations use the CODATA-recommended constants: Planck's constant h = 6.62607015 × 10⁻³⁴ J·s (exact, by SI definition since 2019) and the speed of light in vacuum c = 2.99792458 × 10⁸ m/s (also exact by definition). The result converts to electronvolts using 1 eV = 1.602176634 × 10⁻¹⁹ J.
Inputs and what they mean
Wavelength (λ) is entered in nanometers on the Energy tab — visible light spans roughly 380–700 nm, so this is the natural scale for optics and color. Frequency (f) is entered in terahertz (10¹² Hz) on the From Frequency tab, since raw hertz values for light are unwieldy (visible light sits around 400–750 THz). Whichever field you fill in becomes the source of truth; the calculator keeps the other tab's field in sync automatically.
The output energy is reported in electronvolts (the practical unit for photon-scale physics and chemistry) alongside the SI joule value, since some formulas and textbooks expect joules directly.
Why shorter wavelengths carry more energy
Because E = hc/λ, energy is inversely proportional to wavelength: halving the wavelength doubles the photon energy. This is why ultraviolet light (shorter wavelength than visible light) can break molecular bonds and cause sunburn, while infrared light (longer wavelength) mostly just delivers heat. It's also why X-rays and gamma rays — with wavelengths thousands of times shorter than visible light — carry enough energy per photon to ionize atoms and damage living tissue, which visible or radio photons cannot do regardless of how many of them arrive.
Limits and edge cases
This calculator assumes light traveling in a vacuum (or air, which is close enough for everyday purposes). Light slows down in denser media like water or glass, which changes its wavelength but not its frequency or photon energy — so if you're working with a wavelength measured inside a material, convert to the vacuum wavelength first. The formula also applies to any photon, not just visible light — the Spectrum tab will happily classify radio, microwave, infrared, ultraviolet, X-ray, and gamma-ray photons using the same equation.