Got him!
Non Competing / Cycles / 5.2.0
On Friday, I experimented a lot with light, shadows, glass materials, light and shadow linking, caustics, etc.
Then I had a surprise visit from an old friend who now lives elsewhere, and I didn’t really have time to build and finish the scene I had originally envisioned. So, here’s practically just the rather unfinished test scenario for the scene and the light/shadow concept.
The idea is still clear, I think 
Perhaps this is one of the many pictures I’ll finish later - but this list is really loooong 