How to clean dirty artifacts

Hello guys,
Please help me achieving better rendering. I built an interior scene and after built light I got a lot of very very ugly artifacts in the scene, mostly on walls and on the floor. I boosted the lightmap resolution and built light again but it didn’t change anything, I still have the same ugly artifacts as you can see in the following screenshots. I’m a beginner and I really want to move forward with UE4.Need help please…alt text
Thanks !


Lack of samples!
What is your quality setting under world/lightmass?
Are you using portals? + lightmass importance volume?

Yes there is lightmass importance volume, and yes there are lightmass portals on every windows, the spotlights on the top have 10 as light intensity and 5 as indirect light intensity, under world settings, almost everything is on default settings, except number Indirect bounces lights parameter which is at 10