How to use the photon energy and wavelength converter
- Enter a value and choose its unit: a wavelength, a frequency, a wavenumber or an energy.
- Read the wavelength, frequency, wavenumber and energy in one table.
- Check the region name, such as ultraviolet, a visible color or infrared.
- Use the steps to see which constants and formulas were used.
Formula
Frequency f = c / wavelength, with c = 299,792,458 m/s
Energy E = h f = h c / wavelength, with h = 6.62607015e-34 J s
Energy in eV = E / 1.602176634e-19; per mole = E x 6.02214076e23
Wavenumber = 1 / wavelength in cm; E in eV is about 1239.84 / wavelength in nm
All four constants are exact by definition in the SI system. Values are for a vacuum, where the speed of light is c.
Green light, fiber light and a microwave
Light at 500 nm has a frequency of 599.58492 THz, a wavenumber of 20,000 per cm and a photon energy of 2.479684 eV, or 3.9728917e-19 J. A mole of such photons carries 239.25 kJ. At 1550 nm, used in optical fiber, the energy is 0.799898 eV and the frequency 193.414 THz.
A photon of 1 eV has a wavelength of 1239.842 nm and a frequency of 241.799 THz. A 2.45 GHz microwave has a wavelength of about 122.364 mm and an energy of only 1.0132e-5 eV.
Wavelength, frequency and energy
Light can be described by how far apart its crests are (wavelength), how often they pass a point (frequency) or how much energy each photon carries. They are three views of one thing: shorter wavelength means higher frequency and higher energy. Chemists often use the wavenumber, the number of waves per centimeter, because it is proportional to energy.
For sound and other waves see the speed of sound calculator, for lenses the thin lens calculator, and for the apparent size of a distant source the angular size calculator. Camera filters are covered by the ND filter exposure calculator.
Region names are approximate
The names use rounded boundaries: ultraviolet below 380 nm, visible light from about 380 to 750 nm in the colors violet, blue, green, yellow, orange and red, then infrared, microwave and radio. People and sources draw these lines differently, and the colors blend into each other, so read the name as a guide only.
Assumptions and limits
- Values are for a vacuum. In air, glass or water the wavelength is shorter by the refractive index while the frequency stays the same.
- The Planck constant, speed of light, elementary charge and Avogadro constant use their exact SI definitions.
- The input must be above zero and within the range the page can show, from very short to very long waves.
- Visible color ranges are rounded and approximate, and are meant for labeling only.
Frequently asked questions
How do I convert nanometers to electronvolts?
Divide 1239.84 by the wavelength in nanometers. 500 nm gives 2.48 eV. The page uses the exact constants rather than this rounded shortcut.
How do I convert wavelength to frequency?
Divide the speed of light, 299,792,458 m/s, by the wavelength in meters. A wavelength of 500 nm gives 5.9958e14 Hz, or about 600 THz.
What is a wavenumber?
It is the number of wave cycles per centimeter, the inverse of the wavelength in centimeters. It is used in spectroscopy, where 20,000 per cm corresponds to light at 500 nm.
What does energy per mole mean?
It is the energy of 6.022e23 photons together, in kilojoules. It is the scale chemists use to compare light with the energy of chemical bonds.