In physics and optics, the Abbe number, also known as the V-number or constringence of a transparent material is a measure of the material's dispersion (variation of refractive index with wavelength). Named for Ernst Abbe (1840-1905), German physicist. When stuff moves. ... See also list of optical topics. ... In optics, dispersion is a phenomenon that causes the separation of a wave into spectral components with different frequencies, due to a dependence of the waves speed on its frequency. ... The refractive index of a material is the factor by which electromagnetic radiation is slowed down (relative to vacuum) when it travels inside the material. ... Ernst Karl Abbe Ernst Karl Abbe (January 23, 1840 in Eisenach – January 14, 1905 in Jena), was a German physicist. ... 1840 is a leap year starting on Wednesday (link will take you to calendar). ... 1905 was a common year starting on Sunday (see link for calendar). ...

The Abbe number V of a material is defined as:

where n_D, n_F and n_C are the refractive indices of the material at the wavelengths of the Fraunhofer D-, F- and C- spectral lines (589.2 nm, 486.1 nm and 656.3 nm respectively). Low dispersion materials have high values of V. The refractive index of a material is the factor by which electromagnetic radiation is slowed down (relative to vacuum) when it travels inside the material. ... Solar Fraunhofer lines In physics and optics, the Fraunhofer lines are a set of spectral lines named for the German physicist Joseph von Fraunhofer (1787--1826). ... A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from an excess or deficiency of photons in a narrow frequency range, compared with the nearby frequencies. ... A nanometre (American spelling: nanometer, symbol: nm) is 1. ...

Abbe numbers are used to classify glasses. For example, flint glasses have V<50 and crown glasses have V >50. Typical values of V range from around 20 for very dense flint glasses, up to 60 for very light 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. The materials definition of a glass is a uniform amorphous solid material, usually produced when a suitably viscous molten material cools very rapidly, thereby not giving enough time for a regular crystal lattice to form. ... Flint glass is an optical glass that has relatively high refractive index and low Abbe number. ... Crown glass is either of two kinds of glass. ... In optics, dispersion is a phenomenon that causes the separation of a wave into spectral components with different frequencies, due to a dependence of the waves speed on its frequency. ...

See also:

• Abbe prism
• Abbe refractometer