Location:
The Render Manager > mental ray (Global Renderer)
The Render Manager > (select a pass) > mental ray
Set a current pass and choose Render > Render > Renderer Options from the Render toolbar.
Tab: Importons
Options: Diagnostics [Properties Reference]
Importons are used as the primary mechanism for driving the quality of irradiance particles. Importons are emitted into your scene when you enable irradiance particles. For an explanation of how importons work and how they differ from photons, see Using Importon Maps.
In the context of irradiance particles, you can think of importons as locations where indirect light can be stored. Therefore it is important to cover all parts of the scene that are viewed by the camera with importons, including those areas that are indirectly seen, for example, through a mirror. A Density of 1.0 importon fired per pixel is recommended.
In the case of the mirror scenario, you would also need to allow the importons to bounce in the scene by setting the number of Diffuse Bounces to a non-zero value. More often than not, higher values are useful, but the right number of bounces depends on the scene.
