I am doing few tests with the keyshot trial license before it expires :-) I modeled the room with the cardboard boxes.
The Lamborghini model by Martin Spencer from GrabCad.
The HDRI was 100% black in these renders.
Abed
(http://imageshack.us/a/img268/306/4d6x.jpg)
(http://imageshack.us/a/img706/2772/gfzs.jpg)
(http://imageshack.us/a/img7/1218/nybe.jpg)
Interesting results .... Are you using emitter materials or are the windows/glass low value diffuse ambient light. The final picture is getting pretty close to what you would expect from an interior scene ... I have a load of IES descriptions somewhere too that I have never tried, you got me thinking now - lol
Martin
Yes Martin, interesting results! I have used area light diffuse with Lumen power 2500.
Abed
Keep in mind that you can also dial in the temperature of the light using Kelvin in the color picker.