I created a scene in Blender 3.6.4 with some primitive shapes and some simple lights and little bit of compositing:
It rendered well in 3.6.4, like this:
However, with the same settings in 4.0.2, it's very different:
If anybody knows why and how can I fix this, please share.
Both rendered in cycles
Color management settings:
They're the same.
The .blend file:
Your Point lights have radii of around 2.5 meters, which means they are intersecting the glass objects. They are doing that in the old version as well, but the way the light works was changed.
The behaviour of Point and Spot lights have been changed in 4.0 to be more adequate representations of real life spherical light sources (which does not make sense for spots which I said in a discussion on Blender Project, but anyway) regarding energy conservation and the casting of soft shadows. I'm no physicist or raytracing expert to judge on how much this is true, it's just what was explained by developers in the discussion.
Take a simple setup, a 2×2 m default plane object, then place a Point light directly at its center. I'll give it a Strength of 50 W and a Radius of 0.5 m:
Looking at it top down in rendered view shows the following differences:
The radius on the older version made the shadows softer, but the new version makes absolutely sense because if you would have a brightness falloff within the radius of the light source (like the old version), it would behave as if it was an infinitely small point of light. But if that was the case, it would not cast a soft shadow. So the new version keeps the brightness consistent until it reaches the radius and then you have a falloff - and this makes more sense for a soft shadow as well.
Think of the new Point light with radii > 0 like they are some kind of light bulb with frosted glass. Of course in reality there is a light falloff between the filament and the glass, but you cannot see it from the outside (or only to a certain extent).
