Photon Energy from Wavelength Calculator
Find a photon's energy in eV and joules from its wavelength using E = hc/λ.
✨ What is the Photon Energy from Wavelength Calculator?
The photon energy calculator finds how much energy a single photon of light carries, based on its wavelength. Enter a wavelength in nanometres and it returns the energy in electronvolts and joules, plus the photon's frequency and which part of the electromagnetic spectrum it falls in.
Photon energy is one of the most direct demonstrations of light's quantum nature. Einstein's 1905 explanation of the photoelectric effect established that light delivers energy in discrete packets, photons, whose energy depends only on wavelength (or equivalently frequency), not on the light's intensity. This single idea underlies lasers, solar cells, spectroscopy, and medical imaging.
The key relationship is inverse: shorter wavelength always means higher photon energy. Violet light near 400 nm carries noticeably more energy than red light near 700 nm, and ultraviolet, X-ray, and gamma-ray photons are progressively more energetic still, which is why they can damage cells or ionise atoms while visible and infrared light generally cannot.
This calculator is useful for physics and chemistry students, photography and laser hobbyists, and anyone who needs to quickly convert between a wavelength and the energy of its photons, with the working shown at every step.
📐 Formula
📖 How to Use This Calculator
Steps
💡 Example Calculations
Example 1 - Green laser pointer (532 nm)
Example 2 - Red visible boundary (700 nm)
Example 3 - Germicidal UV-C light (254 nm)
❓ Frequently Asked Questions
🔗 Related Calculators
What is the formula for photon energy?
A photon's energy is E = h c / lambda, where h is Planck's constant (6.62607 x 10^-34 J·s), c is the speed of light (2.998 x 10^8 m/s), and lambda is the wavelength. The result is in joules; dividing by the elementary charge converts it to electronvolts.
How do you convert wavelength to photon energy?
Convert the wavelength to metres, then compute E = h c / lambda. For a quick estimate in electronvolts, use E (eV) is approximately 1240 divided by the wavelength in nanometres, a handy shortcut physicists use for visible and near-visible light.
Why is X-ray light more energetic than visible light?
Photon energy is inversely proportional to wavelength. X-rays have wavelengths of roughly 0.01 to 10 nanometres, tens of thousands of times shorter than visible light's 400 to 700 nanometres, so each X-ray photon carries far more energy, enough to penetrate soft tissue and ionise atoms.
What wavelength range is visible light?
Visible light spans roughly 400 nanometres (violet, highest energy) to 700 nanometres (red, lowest energy). Violet light photons carry about 3.1 eV of energy, while red light photons carry about 1.8 eV.
What is the energy of a green laser pointer's light?
A typical green laser pointer emits at 532 nanometres, which works out to a photon energy of about 2.33 eV, or 3.73 x 10^-19 joules, right in the middle of the visible spectrum.
How does photon energy relate to frequency?
Photon energy is also given by E = h f, where f is the frequency. Since c = f lambda, higher frequency light has a shorter wavelength and higher energy, the two formulas are equivalent ways of describing the same relationship.
Why is electronvolt a convenient unit for photon energy?
A joule is far too large a unit for single photons and atomic processes. An electronvolt, the energy gained by an electron crossing a one-volt potential (1.602 x 10^-19 joules), gives conveniently sized numbers, typically 1 to 10 eV for visible and near-visible light.
What determines the color of visible light from its energy?
Within the visible band, energy and colour are directly linked: violet and blue light have the shortest wavelengths and highest energies, while red light has the longest wavelength and lowest energy. Green sits in the middle, around 2.3 eV at 532 nm.
What is the energy of a typical gamma ray photon?
Gamma rays have wavelengths shorter than about 10 picometres (0.01 nm), giving photon energies above roughly 124,000 eV (124 keV) and often reaching millions of electronvolts (MeV). This enormous energy per photon is why gamma radiation can penetrate deep into materials and damage living cells, unlike visible or infrared light.
How does photon energy relate to photon momentum?
A photon's momentum is p = h / lambda, directly analogous to its energy formula E = hc / lambda. Combining the two gives E = p c, so a photon's energy and momentum are simply proportional, linked by the speed of light. This relationship is what allows radiation pressure and is central to Compton scattering.