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Table of Contents

This page provides information on the GI tab of the V-Ray Renderer parameters.


Global Illumination (or GI) is the illumination in a scene that effectively comes from reflected (or bounced) light as opposed to coming directly from a light source. This enables more naturalistic and accurate lighting solutions.

The bounces of indirect illumination can be classified as primary diffuse bounces and secondary diffuse bounces:

  • A primary diffuse bounce occurs when a shaded point is directly visible by the camera, or through specular reflective or refractive surfaces. V-Ray always uses Brute Force for them.
  • A secondary bounce occurs when a shaded point is used in GI calculations.

For detailed information on the Brute Force and Light Cache settings, please go to their respective page:

For further information on the two types of GI engines, please see the Indirect Illumination Reference page.


On – Enables/disables indirect illumination.

Reflective Caustics – Allows indirect light to be reflected from specular objects (mirrors, etc.). Note that this is not the same as Caustics, which represent direct light going through specular surfaces.

Note: GI caustics represent light that has gone through one diffuse, and one or several specular reflections (or refractions). GI caustics can be generated by skylight, or self-illuminated objects, for example. However, caustics caused by direct lights cannot be simulated in this way. You must use the separate Caustics Tab section to control direct light caustics. Note that GI caustics are usually hard to sample and may introduce noise in the GI solution. For more information, see the GI Caustics example below.

Refractive Caustics – Allows indirect lighting to pass through transparent objects (glass, etc.). Note that this is not the same as Caustics, which represent direct light going through transparent objects. You need refractive GI caustics to get skylight through windows, for example.

Engine – Specifies the method to be used for secondary diffuse bounces.

The previous three post-processing parameters allow additional modification of the indirect illumination before it is added to the final rendering. The default values ensure a physically accurate result, but values can be changed to modify the way GI looks for artistic purposes.

When CUDA/RTX is chosen as a rendering engine, all unsupported options are disabled from the parameters. 

Example: GI Caustics

This example shows GI caustics generated by a self-illuminated object:

Example: Light Bounces

This example shows the effect of the number of light bounces on an image:

GI is disabled

GI is set to None

GI is set to Brute Force

GI is set to Light Cache

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