This page provides information on the Caustics tab of the V-Ray Renderer parameters.


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. The settings in this parameter section control the generation of the photon map.

In order to calculate the caustics effects, V-Ray uses a technique known as photon mapping. It 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 object 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


||Renderer tab|| > Caustics tab

(with the V-Ray Renderer node selected)



Enable Caustics – Turns the rendering of caustics on and off.

Mode – Controls the mode of the caustics photon map.

New – Causes a new photon map to be generated. The new map overwrites any previous photon map left over from a previous rendering.
From File – V-Ray does not compute the photon map but loads it from a file.

Multiplier – Controls the strength of the caustics. It is global and applies to all light sources that generate caustics. If you want different multipliers for the different light sources, use local light settings. 

Note: This multiplier is cumulative with the multipliers in the local light settings.

Search Distance – Specifies the radius of search area circle. 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 original photon and a radius equal to the value. Smaller values produce sharper, but perhaps noisier caustics; larger values produce smoother but blurrier caustics. For more information, see the Search Distance example or the Light Caustics Subdivs example below.

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

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 first looks 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 just adds the energy of the new photon to the one in the map. Otherwise, V-Ray stores the new photon in the photon map. Using this options allows you to shoot many photons (and thus get smoother results) while keeping the size of the caustics photon map manageable.

File – File name with the caustics photon map to be loaded when Mode is set to From File.

Don't Delete from Memory – When enabled, V-Ray keeps the photon map in memory after the scene has finished rendering. Otherwise, the map is deleted, so that the memory it takes up is 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 automatically saves the caustics photon map to the file specified in the Auto save file field when rendering is complete.

Auto Save File – Specifies the file to which the caustics photon map is saved when Auto save is enabled. Click the Browse button to the right to specify the file name.

Show Calculation Phase – When enabled, displays the calculation of the caustics map.




Example: Search Distance

For this image, the Caustics Subdivs parameter of the V-Ray light is set to 50. This makes the separate photons more distinct. In the V-Ray Renderer Caustics tab, the global caustics Multiplier is 1, and Max Photons is set to 0. As seen from the images, the larger Search Distance produces blurrier caustics.


Search Distance = 0.05


Search Distance = 0.5





Example: Light Caustics Subdivs

This example is similar to the previous one, but the Caustics Subdivs parameter for the V-Ray Light is increased to 300. The other Caustics parameters in the V-Ray Renderer are the same as in the previous example. As can be seen in the images, the larger number of photons produces smoother caustics effects than in the previous example. 


Search Distance = 1


Search Distance = 5





  • Caustics also depend on the individual light settings.
  • For accurate caustic calculations, disable the VRayMtl's 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.



Page Contents ×