Unexpected dark area in ShadowsLightsDemo (?)

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.

Hi folks,

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

Output

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?

Thanks,
Elvis

Actually, also wondering about the little light patch on the belly of the sphere.

Noone else who thinks the lighting looks strange? I tried putting a vtkSphereWidget in and moving it around the scene, but didn’t really get any wiser…