The peak wavelength of an LED is typically described by a series of physical quantities. It should be noted that in case of a symmetric line spectrum, the centroid, peak and center wavelengths are identical since they coincide. Only the full width at half maximum value (FWHM) gives differing information.
Peak wavelength, λp
It is defined as the wavelength at which the spectral distribution or line reaches its largest value.
Centroid wavelength, λc
This wavelength defines the position of the spectral center of mass.
Centre wavelength, λs
The center wavelength is defined as the center of the FWHM.
Full width at half maximum (FWHM)
This quantity gives information about the width of a radiator at half the height of its maximum.
Fig. 1: Defining properties of a spectral line