EDIT: Moved topic to the Development category since it’s about one of the official examples. Hope this is OK. Let me know if I should move it back to Support.
Probably I’m just missing something, but I tried the ShadowsLightsDemo with
curl -O https://gitlab.kitware.com/vtk/vtk-examples/-/raw/master/src/Python/Visualization/ShadowsLightsDemo.py python3 ShadowsLightsDemo.py
What is the dark area on the top face of the box? It looks like it ought to be illuminated by the light to the left?