V-Ray for Rhino Manual - Rum

Choosing different Render Engines
In order to calculate indirect light within V-Ray a render engine must be specified to compute those
calculations. Each engine has its own method of calculation and each with its own advantages and
disadvantages
V-Ray is uses two render engines to calculate the final rendered image. Open Indirect Illumination control
panel under Options. There are Primary Engine and Secondary Engine options in the panel below.
There are four options for Primary Engine: Irradiance Map, Photon Map, Quasi Monte-Carlo and Light Cache.
Default is set to Irradiance Map.
There are three options for Secondary Engine: Photon Map, Quasi Monte-Carlo and Light Cache. Default is set
to Quasi Monte-Carlo or you can select None to not use this Engine.
When switching between different engines, the control panels will also change according to the assigned
engine.
Clasification of Light bounces
Direct light- This is the light which is calculated directly from a light source. If GI were not enable, or if
there were no engine selected of either primary or secondary bounces the rendered image would be the
result of only the primary bounces. It is not necessary to specify an engine for these calculations as these
are done through standard raytracing. Environment light is not considered a form of direct light.
Primary bounces- this the light which is the first bounce after the direct light hits a surface. Usually these
bounces have the greatest effect on the scene in terms of the indirect lighting, as these bounces retain a
significant portion of light energy. Environment light is calculated as a primary bounce.
Secondary bounces- this is all of the light which bounces around the scene after the primary bounce. As light
bounces around a scene, its intensity, and therfore its affect on the final illumination, becomes less and
less. Because of this secondary bounces can all be calculated through a single method. With exterior
scenes these bounces have a relatively insignificant effect on the final result, however with interior
scenes the bounces can become as important as primary bounces.
It is important to remember these classifications when evaluating an image’s quality, and adjusting settings
to either achieve better or faster results.
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V-Ray for Rhino