What is the energy of a 500 nm photon?

A photon with a wavelength of 500 nanometres (green visible light) has an energy of approximately 3.97 times 10 to the power of negative 19 joules, or about 2.48 electronvolts. The electronvolt unit is more convenient at the atomic scale because it avoids the small exponents that appear in joules.

Why is shorter wavelength light more energetic?

Because photon energy is inversely proportional to wavelength (E = hc/lambda), halving the wavelength doubles the energy. Ultraviolet and X-ray photons have much shorter wavelengths than visible light and therefore carry more energy per photon, which is why they can cause more biological damage.

Photon Energy Calculator

A photon is the fundamental particle of light and all other electromagnetic radiation. Its energy is determined entirely by its frequency or, equivalently, its wavelength: higher frequency means more energy. The relationship is captured by two equivalent formulas. When you know the wavelength, use E = hc divided by lambda, where h is Planck's constant (6.626 times 10 to the power of negative 34 joule seconds) and c is the speed of light in a vacuum (2.998 times 10 to the power of 8 metres per second). When you know the frequency, use E = hf. Because photon energies at the atomic scale are tiny in joules, results are also given in electronvolts (eV), where 1 eV equals 1.602 times 10 to the power of negative 19 joules. Visible light spans roughly 380 nm (violet, about 3.26 eV) to 700 nm (red, about 1.77 eV). Ultraviolet photons carry enough energy to break chemical bonds, which is why sunscreen matters. X-ray and gamma-ray photons are more energetic still. This calculator accepts wavelength in nanometres or frequency in hertz and returns energy in both joules and electronvolts along with the corresponding frequency or wavelength. It is used in quantum mechanics, spectroscopy, photochemistry, solar cell design and radiation physics courses. Results use internationally accepted constants and are for educational and reference use.

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Input mode

Wavelength (nm)

Frequency (Hz) - for frequency mode

3.97e-19 J

photon energy

Energy in eV2.48 eV

Frequency5.996e14 Hz

Wavelength500.00 nm

Constants used: h = 6.626 x 10⁻³⁴ J s, c = 2.998 x 10⁸ m/s, 1 eV = 1.602 x 10⁻¹⁹ J.

How it works

From wavelength: convert lambda from nanometres to metres (multiply by 1e-9), then apply E = hc / lambda. From frequency: apply E = hf directly. Convert to electronvolts by dividing the joule value by 1.602 x 10 to the power of negative 19. To find frequency from wavelength use f = c / lambda; to find wavelength from frequency use lambda = c / f, then convert metres to nanometres.

Worked example

A photon has a wavelength of 500 nm (green visible light). Converting: 500 nm = 5.00 x 10 to the power of negative 7 m. Energy E = (6.626e-34 x 2.998e8) divided by 5.00e-7 = 1.9864e-25 divided by 5.00e-7 = 3.97 x 10 to the power of negative 19 J. In electronvolts: 3.97e-19 divided by 1.602e-19 = 2.48 eV. These match the default values pre-filled above.

Related calculators

Half-Life Calculator: calculate radioactive decay and the number of half-lives elapsed.
Energy Converter: convert between joules, electronvolts, calories and other energy units.
Velocity Calculator: find the speed of light or other waves from frequency and wavelength.
Percent Error Calculator: compare your experimental photon energy result with the theoretical value.

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