Bosseye wrote:
3) The default material in sketchup looks white, but actually renders a sort of grey which can darken scenes a little - change your wall coverings to a white material (but not pure 255,255,255 white, knock them down a little, too white and you get fireflies - spots of white in the image - I believe) which may help lighten up the interior.
Generally no albedo should be set above 80% reflectance or in essence above 205 for any RGB color component. Materials like this don't exist in nature. Not only does this reduce fireflies but it also reduces the render time.