I want my light looking like this. Its the same what i try, some brushes forming a grid or cage with a light behind casting well looking shadows.

And this is my testmap with my very bad looking result 
Also the wall is to dark compared with the floor and the ceiling.

lightmapscale 0.5
samples 3
samplesize 4
Whats wrong ? Ive played around with nearly all settings and got only shitty shadows all the time 
Or heres another example how it should look :
