# Abbe Number

Written by Jerry Ratzlaff on . Posted in Dimensionless Numbers

Abbe number, abbreviated as $$V_d$$, a dimensionless number, is the measure of material's dispersion (variation of refractive index versus wavelength) with high values of V indicating dispersion.  It is used to classify glass and other optically transparent materials.

## Formulas that use Abbe Number

 $$\large{ V_d = \frac{ n_d \;-\;1 }{ n_f \;-\; n_c } }$$

### Where:

$$\large{ V_d }$$ = Abbe number

$$\large{ n_c }$$ = refractive index at the wavelengths of the Fraunhofer C spectral line

$$\large{ n_d }$$ = refractive index at the wavelengths of the Fraunhofer D spectral line

$$\large{ n_f }$$ = refractive index at the wavelengths of the Fraunhofer F spectral line