Quote - you-know-who may add caustics at some point, but there may be ways to fake it that are quicker.  like some things (e.g. transparency colour) are not really caustics - they work in some apps with caustics disabled.

*Transmission caustics. Is that not right? Shadow was not the correct word.  This picture is what I mean so I'm clear. *

Light passing through or not is just transmission. This is the opposite of casting a shadow - it simply not casting a shadow.

Caustics are when transmitted light beams from different places of an object are focused, creating a local hot spot that is brighter than simply transmitted light.

A caustic is not possible unless a surface is curved. 

Your image shows both.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)