Within the spectra of the two stars the Li lines show different equivalent widths.

Thus the equivalent width can in many conditions yield the number of absorbing or emitting atoms.

The equivalent width is used as a quantitative measure of the strength of spectral features.

The equivalent width is also used in many other situations where a quantitative comparison between line strengths is needed.

For instance, the equivalent width of a rectangular waveguide compared to a SIW is described in the approximation:

The equivalent width of a spectral line is a measure of the area of the line on a plot of intensity versus wavelength.

The equivalent width is a convenient choice because the shapes of spectral features can vary depending upon the configuration of the system which is producing the lines.

The equivalent width, on the other hand, "measures the fraction of energy removed from the spectrum by the line," regardless of the broadening intrinsic to the line or a detector with poor resolution.

As the filters are located on different telescopes, it is possible to measure the same sky region with both filters simultaneously, deriving the equivalent width of the band for every star in the field of view.

The largest volume of water of any equivalent width anywhere in the world is funnelled into a torrent that you can get to within 10ft of: the noise is tremendous, the huge amount of spray incredible.

For example, measurements of the equivalent width of the Balmer alpha transition in T Tauri stars are used in order to classify individual T Tauri stars as being classical or weak-lined.

Also, the equivalent width is used in studying star formation in Lyman alpha galaxies, as the equivalent width of the Lyman alpha line is related to the star formation rate in the galaxy.