Wavenumber
In science, the wavenumber indicates the number of wavelengths that would fit in a unit of length. The normal units for wavenumbers are inverse centimeters cm-1. A different name for this unit is kayser (after Heinrich Kayser). Light with a wavelength of 500 nm (green) has a wavenumber of 20,000 cm-1 or 20 kK. Photon energy and frequency are proportional to wavenumber: 10 kK corresponds to 1.24 eV.
Historically, wavenumbers were introduced by Janne Rydberg in the 1880's in his analyses of atomic spectra.
Wavenumbers (), wavelength (Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \lambda} ), and frequency () are related: