I haven’t touch the baselightmass.ini. Interior white walls are the worst case scenario you can get for lightmass. It’s really hard to get a “dirt-free” lighting in this situation… But there are some tricks you can use to reduce those those problems. I’ll list the most important ones in my opinion, it may help you:
First of all you must make sure that you have nice unwrap mapping for all your assets and mainly the walls and white surfaces (and set high lightmap res for them).
After that, you must look for light leaking in the corners. Sometimes, if you have a mesh with a portion of its surface exposed to intense light and another portion under shadow, you’ll get light leaking and the solution is to break the mesh into peaces (one for the bright environment, other for the shadows).
Always try to avoid plain white materials. Use at least a normal map to give the walls some texture. Some sort of variation texture on the roughness channel also helps. Unrealparis scene may be 95% white, but if you look carefully you’ll notice a lot of normal textures and stuff on the wall corners. Those helps a lot to hide any lightmass artifacts. And you’ll find some dark spots on that project anyway if you go to dark places (like around the main door behind the player at the very first position).
And finally, you should always avoid regions in your interiors where direct light can’t reach. Make sure to put at least one source of light in every room. Use skyportals for the windows (reflectors with spotlights like the ones in koola’s scene at marketplace) and artificial lights for the rooms without windows or regions of large rooms where natural light won’t reach.
Here is my lightmass setup for that scene:
Have in mind that I’m far from being an expert on this… You can find a lot of dark spots in those images I’ve posted… I’m always trying to improve interior lighting somehow though.
Do you mean to break the walls up into separate meshes or to break up the ceiling into seperate meshes? Or both?