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Caustics are not included in the built-in list because they overlap with
indirectdiffuse lpe:C<RD>[DS]+[<L.>O] However, you can select caustics with the expression
lpe:CDS+[<L.>O] Below you can find an example of the caustics LPE output, Indirect Diffuse, and the difference between them. Note that the Caustics LPE output doesn't capture indirect lighting from object to object, in this case the red cube. You can create the image on the far right with the indirect diffuse minus the caustic result using the following source:
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