VRay for SketchUp Manual
What are Caustics?
Caustic is a lighting phenomena created by some materials, for example,
metal, glass and liquid which either reflect or refract light around the object.
This happens when the light becomes focused by the materials resulting in a
pattern of bright light.
Open file: Chairs-Caustics-01.skp, open
V-Ray for SketchUp's Render Options. Pull down the Caustic control panel at the
bottom. Check the on to open the Caustic effect.
At the beginning of the render the progress window will say that it is
calculating caustics. Depending on the number of lights and the caustic
subdivisions of each light this process may be very quick or take a few minutes.
Image on the left is rendered without Caustic effect. Image on the right is
rendered with it. The values of Max Photons, multiplier, and Caustic Subdivs are
all using default setting. With the image on the left you can see a slight
caustics effect. This is due to the Affect Shadows option. This option is
actually trying to fake the caustics effect seen on the right.
Go back to the Caustic's control panel. Render it again with the Max Photons
changed from 50 to 300, as the image on the right. Compare with the image below
will find the Caustic effect is greater this time and smoother.
Usually it's easier to spot the Caustic effect in a darker scene. If the
scene is brighter, you can try increase the Multiplier to offset the difference.
If you want to control the quality of Caustic even better, other than
increase the intensity of light, you can also increase the Subdivs under
Sampling from 1000 to 2000 or even higher. But this will increase the prepare
time for render Caustic effect.
Image below is rendered with Caustic Subdivs set to 3000, you can see the
better quality of Caustic effect in this case.