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Any piece of geometry can become a light source in RenderMan for Blender.  Select the geometry that should become emissive and click on Convert to Mesh Light button from the object context menu.

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The next time you render, the object will cast light and itself have a constant color which comes from the PxrMeshLight's color and intensity.

PxrBlack

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When the Mesh Light button is clicked, a new material called PxrBlack is assigned to the selection, and a PxrMeshLight is created and wired into the material of the PxrBlack material.  PxrBlack acts as a dummy material.  It doesn't actually have any parameters.

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