BRDF: How Reflectivity Depends on Angle

In the real world, the reflectivity of a surface is often view-angle dependent. A fancy term for this is bidirectional reflectance distribution function (BRDF). This is a way to define how much a material reflects when it is seen from various angles.

The reflectivity of the wood floor depends on the view angle.

Many materials exhibit this behavior. The most obvious examples are glass, water, and other dielectric materials with Fresnel effects, where the angular dependency is guided strictly by the index of refraction (IOR). Layered materials such as plastic, or varnished wood, display similar characteristics.

The Arch & Design material allows this effect to be defined by the index of refraction, and also allows an explicit setting for the two reflectivity values for:

• 0-degree faces (surfaces directly facing the camera)
• 90-degree faces (surfaces 90 degrees to the camera)

Interface

[BRDF method]

Lets you choose how the BRDF curve is defined:

• By IOR (fresnel reflections) When chosen, reflectivity based on angle of view is guided solely by the material's index of refraction. This is known as Fresnel reflections, which model the behavior of most dielectric materials such as water and glass.
• Custom Reflectivity Function When chosen, the following settings determine reflectivity based on angle of view.
  • 0 deg. refl. Defines the reflectivity for surfaces directly facing the viewer (or incident ray).
  • 90 deg. refl. Defines the reflectivity of surfaces perpendicular to the viewer.
  • Curve shape Defines the falloff of the BRDF curve.

Use this mode for hybrid materials (such as varnished wood) and for metals.

For most metal surfaces, you can leave the 90-degree reflectivity parameter set to 1.0, and use the Reflectivity parameter on the Main Material Parameters Rollout to guide the overall reflectivity. On the other hand, the 0-degree reflectivity value for metals is usually high (0.8–1.0).

Layered materials, such as linoleum and varnished wood, have lower 0-degree reflectivity values, in the range 0.1–0.3.

For further information, see Quick Guide to Some Common Materials.

Reflectivity vs. Angle graph

Depicts the combined effect of the Custom Reflectivity Function settings.