Lighting problem

ok it’s clear.
In this case I have a door with a resolution of 2048 (very high). I don’t know why but the lighting in this object looks really bad. Why does it happen? Yet when I import this mesh I don’t get any error message!

From what I understand, every space is close to Light Source will result good in quality, even if the lightmap is not so high. In this case the door is a complex object and it’s far from the window that receives the sun light. So, how can I solve this problem?

Or maybe at this stage I can start to assign the materials, without paying attention to the lighting leakage…?