The IOR (index of refraction) depends on the wavelength of the light entering,
in many materials it is slightly larger for blue light than for red light.
This for example allows to split a beam of white light in a rainbow with a glass prism.
To model the dispersion we use the two-term form of Cauchy's equation.
- index is used as the A parameter. This input increases or decreases the IOR for
- dispersion_coefficient_B is used as the B parameter, and controls the amount
of dispersion. Increasing this parameter increases the dispersion effect, and also slightly
increases the average IOR over all wavelengths. A value of 0.0 means no dispersion, the
index input parameter then just gives the IOR for all wavelengths (like in previous versions
The following image compares a prism with index set to 1.3549, and the B parameter
to 0.0 (left) and 0.02 (right). The beam in the right image is split into colors and slightly
NOTE: The absorption parameters have been removed from the specular material as of
version 1.0 beta 2.55. You may use the absorption and scale parameters of the new medium
nodes to achieve the same effect.
Absorption means that the material slightly absorbs light while passing through.
The color resulting from this absorption is dependent on the distance light travels through
the material. With increased distance it will get darker, and if the absorption is colored
it will get more saturated.
This is very different from the transmission input, which only controls absorption at
the surface of the material, which is independent of the size of the object.
To specify the absorption two input parameters are used:
- absorption_color gives the spectrum remaining from white light after traveling
through the material for a certain distance. Only constant colors are supported
- depth_of_absorption specifies the aforementioned distance (in meters). The smaller
this distance, the stronger the absorption will be.
I hope this helps understanding the new parameters,