The value of the refractive index of any transparent material is a function of the wavelength (color) of the light. In general, in the visible spectrum, the index of refraction increases with the frequency. In other words, it is higher for violet light than for red light. Figure 1.3 shows some curves displaying how the index of refraction changes with the wavelength for two typical glasses.
The chromatic dispersion of glasses in the spectral range not including absorption frequencies can be represented by several approximate expressions. The simplest one was proposed by Cauchy in Prague:
This formula is accurate only to the third or fourth decimal place in some cases. An ...