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The term 'caustics' refers to the patterns of light that are created when light passes through a refractive surface, such as glass. So as you can see in this render, I have a glass vase here on the table, and light is passing through it, and we're getting this pattern in the background, and these are what's known as caustics. You can create this effect using Global Illumination. In this movie, I'll show you how to activate caustics in the scene. So, I'm going to store this image and minimize the render view, and so here's my scene, and I'm going to do a render to see how it looks so far.
So I have a transparent surface. Light is passing through it, and it's creating this type of shadow on the background. And it's a nice, transparent shadow, but in reality, it doesn't actually reflect what happens in reality, because we're seeing a very clear, well-defined shadow. This is something you might see with maybe plastic or something like that, but the shadow itself is not picking up the refraction that the glass surface has in it. So, I'm going to store this image and minimize the Render view. When you create caustic light patterns, you're going to use Global Illumination photons.
So, just like with Global Illumination, when you're trying to create indirect lighting, it's a good idea to separate your direct lighting from your indirect lighting effects. So, I'm going to have two lights. The first spotlight is casting the shadow and creating the lighting the scene. I'm going to duplicate this light and activate the caustic settings for it. So that will just be in charge of creating the caustic light pattern in the scene and not the direct lighting. So I'm going to select light in the Outliner, do Ctrl+D to duplicate it, so now the light is duplicated.
I have the light selected in the Outliner. I'm opening up the Attribute Editor to the spotLightShape2 tab. In this case, I can set the Intensity to 0, and I can set Decay Rate to No Decay. This will have no effect. I'm going to scroll down to the Caustics and Global Illumination settings in the light, and I'm going to turn on Emit Photons. I'm going to pull up my Render Settings here and switch to the Indirect Lighting tab. In the Indirect Lighting tab, there is a Caustic section underneath Global Illumination.
So I'll expand this, and I'm going to turn on Caustics, and I'll just leave the settings at their default, just to see what we get. So, I'll minimize this, and I want to change the position of the light a little bit, so I have the light selected in the Outliner, and I'm going to choose Panels > Look Through Selected Camera, so that I can see exactly what the light is seeing in the scene. Now we only need to create caustics right behind the vase here on the table, so I don't need to be pulled out this far. So I'm going to zoom in and then change the position of the light just a little bit, and in the Attribute Editor for the light, I'm going to lower the cone angle just to get a little bit tighter around the vase.
So, I'm going to switch back to the Perspective view, create a render and see how it looks. So we can see that caustics are activated, you can see the photons of light coming through. You'll also notice that the shadow now looks different. It's not 100% transparent. This is actually more realistic, if you compare it to photographs in the real world. We're going to have something that resembles an opaque shadow, but the light passing through the surface is going to be scattered in the background. The next step that we need to do is start to tune these settings so that we get more of a well-defined pattern.
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