Page "Abbe number" Paragraph 6

Abbe numbers are used to classify glass and other optically transparent materials.

For example, flint glass has V < 50 and crown glass has V > 50.

Typical values of V range from around 20 for very dense flint glass, around 30 for polycarbonate plastics, and up to 65 for very light crown glass, and up to 85 for fluor-crown glass.

Abbe numbers are only a useful measure of dispersion for visible light, and for other wavelengths, or for higher precision work, the group velocity dispersion is used.