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The value set initially is automatically reduced by the solver during successive passes, by up to a fourth of the initial value. For example, with the default value of 4, the search radius after being reduced becomes 1 pixel, allowing for detail to be resolved with that accuracy. If the initial radius is set to 16, the final radius is 4 pixels making the caustics look blurrier.

It is recommended to leave the radius at its default value of 4



Caustics – Enables or disables rendering of caustics.


Progressive Caustics

Multiplier – Controls the strength of the caustics. It is global and applies to all light sources that generate caustics. Should a different multipliers for each light source be needed, the V-Ray properties of each light should be edited. Note: this multiplier is cumulative with the multipliers in the local light settings.

It should also be noted that changing multipliers, while useful for artistic purposes, results in physically-inaccurate scenes.

Search Dist (Pixels) – Specifies the initial photon lookup radius in pixels. The Progressive mode works works only in Pixels.

UI Text Box
UI Text Box

Tips when working with progressive caustics:


  • Affect Shadows should be off in refractive materials if they are to generate caustics
  • The Affect Channels option should be set to Affect all Channels in refractive materials to ensure the Caustics render element contains also the ones fallen behind refraction.
    Not doing so leaves photons fallen behind refractive surfaces inside the Refraction RE, but not inside the Caustics one
  • If present, the VRaySun's photon emit radius should be set to a value large enough to encompass the relevant parts in the scene


  • It is strongly recommended to set time limit when rendering with Progressive Caustics, rather than relying on Noise Threshold value only.
  • Lower the Shading Rate.
    Photons are cast for each camera ray, not for the secondary ones. The more camera rays are cast, the more photon passes are achieved.
    A value of 3 is fine if rendering with the rest of the scene, but a value of 1 could be used if rendering specific caustic passes (for example, a caustics pass scene prepared with the purpose of maximizing caustics' calculation speeds).

Managing Expectations:

  • The progressive caustic solver is fire and forget
    This means that it can be turned on in any scene, and expected to trace photons on any specular or refractive surface.
    It doesn't, however, mean that doing so results in an image converged to perfection within a short time.
    The approach, novel as it is, is still photon-map based, and judgement should be used to ensure quick, noise and frustration-free results.
  • It renders with the beauty
    The solver does indeed render happily alongside a beauty pass, storing caustics in the appropriate Render Element (see requirements tips above!), but that may not be the best solution as far as performance is concerned.
    It's suggested to consider preparing a dedicated caustic rendering pass if the photon tracing is particularly extensive, and/or if sequences are to be rendered.
    That way, it is possible to optimize the caustics calculation separately from the requirements of the beauty pass.






Fancy Bullets
  • they require the progressive image sampler;
  • the image sampler often requires Minrequires Min. subdivs values much higher than 1;
  • it's non-deterministic, meaning that there could be somewhat unpredictable render times, and also tiny differences in the visual results when rendering the same frame twice;
  • currently doesn't work with distributed rendering;
  • currently not supported by the GPU engine;



  • Depending on the scene, the performance might not scale linearly with the number of threads/cores, resulting in inefficient CPU utilization.