The LightMesh can create light sources that have volume and shape without the need to use self illuminated objects and global illumination.

If the LightMesh object is close to other surfaces in the scene, it is best to use it with GI enabled so V-Ray can use combined direct and GI sampling for the mesh light. Without GI, the light might produce noisy results for surfaces that are very close to it.

The LightMesh shader works only with polymesh objects.

Step-by-step guide

  1. Create a simple scene - 2 PrimitiveCreate nodes and one CameraCreate node
  2. Merge them together
  3. Select one of the PrimitiveCreate nodes - set its name parameter to "/root/world/geo/plane" and its type parameter to "poly plane"
  4. Select the other PrimitiveCreate node - set its name to "/root/world/lgt/torus" and type to "poly torus"
  5. Move the torus above the plane and scale the plane to be a bit bigger
  6. Move the camera in the viewer, so the torus is fully visible.
  7. Create a Material node and place it between the PrimitiveCreate for the torus and the Merge node
  8. Create a MaterialAssign node and place it between the Material and the Merge nodes
  9. Assign the Material to the torus
  10. Add light shader in the Material
  11. Set the shader to LightMesh
  12. Change the color parameter of the LightMesh shader to red (1 0 0)
  13. Attach RenderSettings node to the Merge node and set the renderer to vray
  14. Render from the RenderSettings node (right click → Preview render)

 

After you execute these steps you should get something that looks like the image below:

Light linking

Light linking for mesh lights is supported, but in order to apply illumination or shadow rules to the mesh light, you need to first add the mesh light object to the global list of lights. This is done with the LightListEdit node.

Add the scenegraph location of the mesh object in the locations parameter of the LightListEdit node.

After the light is added to the global light list you can change which objects get illuminated by the mesh light or which objects cast shadow from the mesh light. This is done with the LightLink node.