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Like the Geometry Light tool, this tool:
Creates a Light object.
Sets the Light type parameter to Geometry.
Sets the Geometry object to the object you select.
This tool also:
Copies the volume’s shader into the new light’s Material parameter. This ensures that changes to the volume’s colors also affect the light.
Enables generation of a point cloud (stored in temporary memory using the
temp:file prefix). Point clouds often speed up lighting from highly variable volume sources such as volumetric fire. To render the volume light without generating the point cloud, just turn off Light ▸ Area light options ▸ Enable point cloud.
Geometry Light, creating a volume light does not turn off the display flag for the original geometry.
The original volume is left in the scene so that it still shows up in the render.
Use the light object’s attenuation and spot light parameters to adjust the volume lighting if the physically correct defaults aren’t what you want.
Select the volume geometry you want to emit light.
On the Lights and Cameras shelf tab, click the Volume Light tool.
This creates a new Light object and sets it up to emit light based on the volume.
The volume light takes over the emission (
Ce) component, which is treated as direct lighting for the new light source - making it possible to separate it into a distinct per-light deep raster plane separate from the combined
Emission is disabled on the original object for all secondary rays (such as reflections) by disabling the Emission illuminates objects property on the source object. This ensures only the new light object directly illuminates other objects. (This property is on the Shading tab of the source object if you want to re-enable it.)