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.
Displays the name of the shape used as a Mesh Light.
Displays and renders the original mesh shape chosen to represent the Mesh Light.
Makes the light source visible to the camera.