From LuxRender Wiki

The fresnel textures are special textures used for loading optical data into the volume system. They are neither float nor color textures, they are their own type entirely and cannot be used on normal fields.

Fresnel Texture Types

Constant

• Output value: fresnel

Description

The constant texture is the simplest fresnel texture, it takes a single value, an index of refraction. This texture is not well-suited to using glass2 with dispersion enabled! One of the other fresnel textures should be used instead.

Parameters

• IOR: The value for n, the index of refraction

Cauchy

• Output value: fresnel

Description

The cauchy texture takes values to Cauchy's Equation, either n and b, or A and b, you can choose which.

Parameters

• Use IOR: Enter a value for n and b and let LuxRender solve for A, rather than entering A and b and solving for n. Values for n and b are often easier to find on the internet.
• IOR: If Use IOR is enabled, you can enter the value for n here. It is the same as the IOR field for constant.
• A: If Use IOR is disabled, you can enter the value for A here.
• b: The value for b, this value is required.

Sellmeier

• Output value: fresnel

Description

The Sellmeier texture allows you to enter optical properties using the Sellmeier Equation

Parameters

Sellmeier has six parameters normally, and an optional seventh for A. These are the values of the same name in the Sellmeier Equation. Note that wavelengths are in µm, not nm!

• B₁
• B₂
• B₃
• C₁
• C₂
• C₃
• A: This value is not required, but you can add it if you have it.

Sopra

• Output value: fresnel

Description

The Sopra texture is for loading nk files in the Sopra format, such as from the FreeSnell pack.

LuxPop

• Output value: fresnel

Description

The LuxPop texture is for loading nk files in the LuxPop format.

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