Hello, thank you for your answer but since I am Greek the technical terms might be difficult to understand. So what is bounces and caustic issue? I now rendered the same project 2 rooms, one with lights from lib 17 and one room with rooms with lights from lib 20 and realized that the problem is with the lights from lib 20 which makes me realize that the problem is not a general setting of the rendering but sth from the actual lights settings. Any ideas? I attach the pic, op the left side is the room with the light from 20 and the right is lights from the lib 17
Turn off the 3D fixture lights (so you just see the 3D model bits) and use the 'generic' light sources from the ArchiCAD version you are rendering with, so you have the same settings for all sources.
You can also brighten the interior by just using a few generic lightsources, if render times are getting crazy high. I find that f/4.0, iso 400 and 1/125 shutterspeed are plenty bright for interior renders.
These 'generic' sources are basically 'invisible' and just cast a lot of light, shadow, etc and a very adjustable in what you want them to do. For a really quick fix, drop one behind your camera (sort of acts like camera flash).
You can use 'light emitting' surfaces for the lightbulbs etc. These basically add a bit of glow, but don't really cast light. It just helps with the illussion of them casting light.