1.11 Defining Properties of a Spectral Line
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, λ_{p}It is defined as the wavelength at which the spectral distribution or line reaches its largest value.

Centroid wavelength, λ_{c}This wavelength defines the position of the spectral center of mass.

Centre wavelength, λ_{s}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.
High quality measuring devices provide these spectral line evaluations information either in the application software, software development kit or directly on the display in the case of mobile measuring devices like spectral luxmeter. Of course a proper and accurate implementation of the mathematical analysis is important. This spectral analysis is becoming increasingly important, especially in LED measurement technology.
Note: The dominant wavelength is often considered as wavelength information, but strictly speaking it is color information, see definition of dominant wavelength.
Fig. 1: Defining properties of a spectral line