wavelength [λ]
distance in the direction of propagation of a periodic wave between 2 successive positions at which the phase is the sameUnit: mNOTE 1 The wavelength in a medium is equal to the wavelength in vacuo divided by the refractive index of the medium. Unless otherwise stated, values of wavelength are generally those in air. The refractive index of standard air (for spectroscopy: T = 15 ° C, p = 101 325 Pa) lies between 1,000 27 and 1,000 29 for visible radiation.NOTE 2 λ = ν / v, where λ is the wavelength in a medium, ν is the phase velocity in that medium and v the frequency.NOTE 3 In optical radiation the units “nm” and “µm” are generally used.