GI caustics represent light that has gone through one diffuse, and one or several specular reflections (or refractions). GI caustics can be generated by skylight, or self-illuminated objects, for example. However, caustics caused by direct lights cannot be simulated in this way. You must use the separate Caustics section to control direct light caustics. Note that GI caustics are usually hard to sample and may introduce noise in the GI solution. For more information, see the GI Caustics example below.
Refractive Reflective GI caustics – Allows indirect lighting to pass through transparent light to be reflected from specular objects (glass mirrors etc). Note that this is not the same as Caustics, which represent direct light going through transparent objects. You need refractive GI caustics to get skylight through windows, for example.
Reflective specular surfaces.
Refractive GI caustics – Allows indirect light to be reflected from specular lighting to pass through transparent objects (mirrors glass etc). Note that this is not the same as Caustics, which represent direct light going through specular surfaces. While the result is more realistic, this may produce some undesired subtle noisetransparent objects. You need refractive GI caustics to get skylight through windows, for example.
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When the render engine is set to CUDA, the Reflective/Refractive Caustics options are always enabled and are hidden from the UI.