• This lesson will take you through setting up caustics with V-Ray
  • This information centers around the basic caustics parameters
  • The lesson topic is approximately 20 minutes in length
  • This lesson covers all 3 Learning Cycles for the Lesson Topic – Lecture, Demonstration, and Activity




Available Materials
Additional resources



Goal - Develop the look for a glass dog and his shadow. Use various caustics parameters to create different looks  

Objective – We will use several parameters to set up and alter caustics in a scene                                                          

Outcome – You will understand how to work with the caustics parameters to  create a specific look



Available materials

To set up the lesson follow the links below and download all available materials.

Lesson plan download
Presentation (Lecture) download
Demonstration tutorial download                                                                  

Scenes & Assets download           



1. Terminology

Here are some terms to be aware of when thinking about caustics.

  • Caustics
    • Light reflecting or refracting off a curved surface
  • Photon
    • Unit or “particle” of light


Caustics vs. Refraction

  • Caustics affect what the light does; Refraction affects the material
  • Caustics affect highlights and shadows on nearby surfaces
  • Qualities of refractive material affect appearance of shadow
    • When caustic light passes through an object and hits a surface, highlights and shadows on surface are based on object’s reflective/refractive material properties




2. V-Ray Caustics

a) Caustics Overview

  • Turn on caustics in Render Settings window
  • Change caustics settings for light
  • Change refraction settings for material



A light’s attributes that affect caustics appearance:
  • Caustics subdivs
  • Photon radius
  • Refraction IOR and Fresnel IOR


Turn on caustics
  • Render Settings > GI tab > Caustics rollout



b) Caustics subdivs
  • Sets quality of detail in caustics; higher values give more detail
  • Parameter found under settings for the light
  • Effect is most easily seen with caustics render element




c) Photon radius
  • Sets a radius in which the V-Ray Sun is going to emit photons to be used for the calculations of caustics
  • Parameter found under settings for the V-Ray Sun




d) Refraction IOR and Fresnel IOR
  • Parameters affect refraction for material, which in turn affects caustics

Effect is most easily seen with caustics render element



e) Dispersion
  • Affects material
  • Disperses light by wavelength, as with a prism
  • Higher Dispersion Abbe makes the dispersion effect stronger
  • Colors visible in caustic shadows






a) Caustics subdivs
  • Level of detail for caustic effect
b) Photon radius
  • A radius within each photons are traced
c) Refraction and Fresnel IOR
  • Affects caustics via material the light passes through
d) Dispersion
  • Scatters light into colors in material; affects caustics via material            


Time to see it work!

Watch while I demonstrate how to set up caustics              

Demonstration tutorial





Time to do it yourself!

Use the provided  scene file to set up and adjust caustics.
We have also provided a final scene for your reference.


Dialing in the right values

  • Photon radius – 3.000
  • Caustic subdivs – 1500                        
  • Dispersion Abbe – 15

Additional resources

Find more training resources listed below: