I’m having some troubles obtaining an “all white” surface.
As you can see from the attached image I have a “dirty” effect despite having high light map resolution (red), good ligthmass setting, and a material with only a white colour node on the diffuse, no normal or anything. The scene has been built with production quality, using an hdri with nomipmaps on mip gen settings, static light.
Many thanks in advance!
Try restoring the parameters to their default values
Looks like lack of samples…
IMO your lightmass settings are not the best… Your ILQ is a bit low for an archviz scene, you should try with 8!
And also your ILS is way too high!! Like this you will lose all your detailed calculation! In my experience the best is to go with 0.6!
…is your scene covered with a Lightmass Importance Volume?
Happened to me in the past that the HDRI was not the best quality and caused artifacts on my renderings! Have you tried with different HDRI?
Are you using GPU Lightmass? Because none of those settings do anything for GPU Lightmass.
If you’re using CPU lightmass, as Makigirl said your ILS is way too high and your ILQ is too low.