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titleUsing Meshlight

The above parameter for "Light Source" is useful for many applications when using a volume with emission properties. But there may be times you need to control the influence of the light from the volume. This requires the use of a light filter. The PxrVolume material doesn't have a way to use a light filter so you can apply the PxrMeshlight material to the volume object along with the PxrVolume for shading.

In doing so this will light the scene but allow you to connect and use a light filter through the meshlight controls. But there is a caveat to this workflow that requires extra consideration in your setup.

When you apply the meshlight to the volume you may notice an increase in illumination and/or additional noise. This is because of double contribution of the volume emission and the meshlight itself. Here are the current steps to reduce this issue.

Note

If you do not need a light filter then this work is unnecessary, simple use the "Light Source" parameter.

  1. Duplicate your original volume
    1. On the duplicate, assign a duplicate PxrVolume with the correct pattern connections to the original patterns you may be using to drive emission, density, etc
    2. Assign a PxrMeshlight to the volume using the DCC application options (SG Node, Material Builder, etc)
    3. Hide this volume from camera and indirect visibility, we only want the light contribution.
  2. In the original volume, disconnect the emission, this will now be lit by the duplicate volume's meshlight source. This prevents double light contribution
  3. Apply a light filter as needed to the duplicate volume with meshlight

Examples:

Using Light Source

Adding the meshlight increases light in the scene and noise, this is the incorrect workflow

This image is using the above workflow to create a well converged render while allowing use of a light filter


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