Create a mental ray area light using the standard procedure in Maya. See Create a Maya light source for more information.

To create a mental ray area light

1. Select Create > Lights > Area Light.
2. Open the Attribute Editor ( +a).

   The Attribute Editor displays the selected light’s attributes.

3. Click the lightShape tab, expand the mental ray section, then expand the Area Light subsection.
4. Check the Use Light Shape option to turn the Maya Area Light into a mental ray for Maya Area Light. Select from the drop-down list the desired shape for the mental ray area light source.
5. Adjust the Area Light settings as desired, making sure to turn on the Visible flag if you want to make the area light visible in the final rendering. (Typically, light sources only illuminate a scene and are not visible to the camera. If you want a light to be visible (a table lamp or light bulb, for example) or to show up in reflections, you need to make it explicitly visible. This does not affect the light contribution of the light.)

   See mental ray attributes for lights (point, spot, directional, area).