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To create a holdout light (a light source that directly illuminates other holdouts), create a light using "__illumholdout" as the light group suffix. This tells integrators to consider this light as a new light source when illuminating holdout geometry.
Light "PxrSphereLight" "spherelight" "string lightGroup" ["light__illumholdout"]
Shadows and Compositing
A holdout shadow pass can be output using the PxrShadowFilter plug-in. The occluded and unoccluded input AOVs should be rendered using the holdouts LPE prefix.