www.kraytracing.com

follow janusz what he said. and u will be good.

for my point when i saw ur render . i think u need good tonemaping setup

her my poste for u render .

dont use lumi panel on ceiling . my openion .

and i see u have poor materiel there and quality render also .

and about backdrop hdri using kray in interior . its useless . use physky alltime .

mybe if u have some big window and u want to get true color like nature . use hdri in backdrop . otherwise its useless to use it when u have small window ordinary house .

Use one Area light out side . and good luck . tone map as this is good : "Lwf " 1.2 - 1 | 2.2 . 1 . 3.5 . 1.0

Thanks for all the advice!
Soon gonna post final images and then gonna leave for a holiday!

Here are final results :

Looks good

btw
for better GI (sharp GI corner effect) we must wait for K3. With K2 engine is quite difficult to get good looking corners - the radiation is too big always. Path Passes option (for example 1/50%) helps detect these regions by cached Path Tracing Photons but effect is average...of course without is much worst.

This bad effect comes from not accurate photons (which is normal and exist everywhere in other software) G. add just small tool (path passes) which support this imperfection by small amount Path Tracing Photons.
K3 has new Photon engine which make accuracy close to Path Tracing! but with Photon Mapping system (so ~10-20 times faster)...something similar to Sky Portals. After that having good photon map sampling will be very good and fast.

Thanks again for all the advice, for the first time I actually enjoyed doing an interior
Can't wait for K3.

btw
I know about some difficulties in Kray (GI, light, sampling, AA) but also they exist everywhere in other softwares. Good idea is just to try render with Maxwell, V-ray, Modo, Octane to feel it on your own skin

Anyway I have no doubts with K3 Engine - completely new software without weak points. For that we must wait because beta phase is difficult (it will be faster then K2 for sure but it will take time)