7.1.4 Dispersion

From [pov:6.6.5]:
For all materials with a ior different from 1.0 the refractive index isn't constant throughout the spectrum. It changes as a function of wavelength. Generally the refractive index decreases as the wavelength increases. Therefore light passing through a material will be separated according to wavelength. This is known as chromatic dispersion.

By default POV-Ray does not calculate dispersion as light travels through a transparent object. In order to get a more realistic effect the dispersion and dispersion_samples keywords can be added to the interior block. They will simulate dispersion by creating a prismatic color effect in the object.

The dispersion value is the ratio of refractive indices for violet to red. It controls the strength of dispersion (how much the colors are spread out) used. A DISPERSION_VALUE of 1 will give no dispersion, good values are 1.01 to 1.1.