This page provides information on the Caustics rollout of the V-Ray GI Render Settings.


Page Contents



V-Ray supports the rendering of the caustics effects. In order to produce this effect you must have proper caustics generators and caustics receivers in the scene (for more information on how to make an object a caustics generator/receiver read the V-Ray Object Properties and V-Ray Light Settings pages). The settings in this parameter section control the generation of the photon map required for caustics.

In order to calculate the caustics effects, V-Ray uses a technique called photon mapping. Photon mapping is a two-pass technique. The first pass consists of shooting particles (photons) from the light sources in the scene, tracing them as they bounce around the scene, and recording the places where the photons hit the objects' surfaces. The second pass is the final rendering, when the caustics are calculated by using density estimation techniques on the photon hits stored during the first pass.



UI Path: ||V-Ray GI render settings|| > Caustics rollout



Enable caustics – Turns caustics rendering on and off. Enabling this option will expand the tab to show all parameters.

Max photons – Maximum number of photons that will be considered when rendering the caustics effect on a surface. Smaller values cause less photons to be used and the caustics will be sharper, but perhaps noisier. Larger values produce smoother, but blurrier caustics. The special value of 0 means that V-Ray will use all the photons it can find inside the search area.

Search distance – When V-Ray needs to render the caustics effect at a given surface point, it searches for a number photons on that surface in the area surrounding the shaded point (search area). The search area is a circle with its center at the photon on the surface, and a radius equal to the  Search distance  value. Smaller values produce sharper, but perhaps more noisy caustics; larger values produce smoother, but blurrier caustics. See the Search Distance example below.

Max density – Limits the resolution (and thus the memory) of the caustics photon map. Whenever V-Ray needs to store a new photon in the caustics photon map, it will first look to see if there are any other photons within a distance specified by Max density. If there is already a suitable photon in the map, V-Ray will just add the energy of the new photon to the one in the map. Otherwise, V-Ray will store the new photon in the photon map. Enabling this option keeps the size of the caustics photon map manageable while shooting many photons and thus getting smoother results.

Multiplier – Controls the strength of the caustics. This parameter is global and applies to all light sources that generate caustics, and is multiplied by any multiplier parameters in local light settings.

Mode – Sets the mode of the caustics photon map:

New map – A new photon map will be generated which will overwrite any previous photon map left over from a previous rendering.

From file – V-Ray will not compute the photon map but will load it from a file. Click the Browse button to specify the file name.

Save – Save an already generated photon map in a file.

Reset photon maps – Removes stored caustics map from memory.

Don't delete – When enabled, V-Ray will keep the photon map in memory after the scene rendering has finished. Otherwise the map will be deleted and the memory it occupies will be freed. This option can be especially useful if you want to compute the photon map for a particular scene only once and then reuse it for further rendering.

Auto save – When enabled, V-Ray will automatically save the caustics photon map to the file provided in the  Auto save file  field when rendering is complete.

Auto save file – The file name to be saved when Auto save is enabled.

Browse  – Choose the caustics photon map file to be loaded when the Mode is set to From file.

Show calculation phase – When enabled, the samples that are traced are shown. This does not affect the calculation of the caustics map and is provided only as a visual aid.




Example: Search Distance

For this image, the Caustics subdivs parameter for the lights are set to 30 so that the separate photons are more distinct. The Multiplier value is 1, and Max photons is set to 0. The larger Search distance produces blurrier caustics.


Search distance  = 0.5 Inches


Search distance  = 12.0 Inches






Example: Light Caustics Subdivs


This example is similar to the previous one, but the  Caustics subdivs  parameter for the lights are increased to 300. The other parameters are the same as in the previous example. The larger number of photons produces smoother caustics effects than in the previous example.


Search distance   = 0.5 Inches

Search distance  = 12.0 Inches





In order to setup a material to generate caustics, it must be placed above the Base Shader in the shader tree and given it's own individual shader. This is essentially making a wrapper material to control the caustics properties of the individual material. Order is important, so make sure the Shader is stacked on top of the VRayMaterial. 


Glass and Metal materials (blue) are placed above the Base Shader (red).



Enable V-Ray Object Properties of the individual Shaders and increase the Generated caustics multiplier as needed.




  • Caustics also depend on the individual light settings (see V-Ray Light Settings ).
  • For accurate caustic calculations, disable the V-Ray Material Affect Shadows parameter when using caustics. Simultaneous usage of both Caustics and Affects Shadows can be used for artistic purposes but will not produce a physically correct result.