An example mesh light scene can be found here.

 

The current limitations when using a mesh light are: 

 

To create a mesh light, select a mesh and go to Arnold->Light->Mesh light. A separate node is created to represent the mesh light source which references the shape node and has the same attributes as a regular light. It should be visible in Maya windows, such as the Light Editor, Light-linking Editor, etc.

 

Sphere converted to Mesh light with 'Light Visible' enabled

Changing the mesh parameter "translator" to "mesh_light" is still supported, however, it is now considered as deprecated and will be removed in the long-term future.

Mesh Attributes

 

In Mesh 

Displays the name of the shape used as a Mesh Light.

Show Original Mesh

Displays and renders the original mesh shape chosen to represent the Mesh Light.

Light Visible

Makes the light source visible to the camera.

 

 

You may need to increase the number of subdivision iterations for the mesh light if the color texture is clearly visible in specular reflections. For example, this may be evident in a scene where a TV screen is reflected in a glass window.

Mesh Light vs Emission