Thank you both, @glitchered and @pezzott1,
@glitchered, I usually lose some information from your posts due to the way you write — maybe due to excesive informality or slangs? I’m not sure, since English isn’t my native language. By the way, I live in Europe, and we have ceiling fans. Also, that 3D fan is already spinning much slower than my real-life fan at its minimum speed — a tradeoff I had to make to reduce ghosting.
And yes, it’s definitely a real use case: a user might want to study the sun’s movement without having to wait an entire day, but a couple of minutes. That’s just a light changing over a “loooong” time, compared to almost every game having instant on/off lights, which is a much worse scenario for this issue.
GI has to be dynamic in this case, since it’s a complex ArchViz project where many meshes can be changed in real time.
Thank you @pezzott1, only that first cvar helped a very little, with values like 0.5–0.7, but the issue is still quite noticeable.
I’ve isolated the issue further, trying to clear up some of your doubts. Here’s a video showing the problem at an unrealistically 18rpm slow speed, with fixed lighting in the scene (which obviously improves things, however it’s not a solution, just a tradeoff or downgrade):
Thank you!