You need to use portals for interiors with light coming in from outside. I don't know about inside lighting. There are tutes available that have settings. Do a Google on luxrender portals. Arnold has similar problems with interiors. And Arnold is not readily available and who knows when it will be and for how much. It's very nice, but free and ready now is better. :)

Here's the tute I posted earlier for portals... info near bottom of page...
http://www.luxrender.net/wiki/index.php?title=LuxBlend_tutorial:_creating_a_simple_interior_scene

There is an interior light in the scene.

I did opt to try Octane Render and hopefully this weekend I'll have time to finish my new computer  (I finally have all the parts for) to use it. I like the results I've seen from users so much I bought two licenses!

Kevin