"https://en.wikipedia.org/wiki/Abbe_number"^^ . "Constringence"@en . "Abbe Number"@en . . "V-number"@en . . . "In optics and lens design, constringence of a transparent material, also known as the Abbe number or the V-number, is an approximate measure of the material's dispersion (change of refractive index versus wavelength), with high values of V indicating low dispersion." . . "V" . .