Different Ways to Light a Bedroom

Ending this series on lighting is interior lighting. Compared to a character and an exterior set, I found interior set the most difficult to light. Here is why.

Interiors are enclosed space usually lit naturally by sunlight. This means the only light sources are openings such as the windows on the images above. The big question is how do we bounce light from the windows to all other parts of the room? (This bounce light question can be answered easily in the two other cases. For characters, we simply add more fill lights. For exterior set, the need for bounce light is minimized by lighting from the sky.) There are two answers that I know of.

The first is using Final Gather to bounce the light. This is, after all, what Final Gather was designed to achieve. The first image was rendered using this method.
The main disadvantage of this method is render time. The Final Gathering step took 2+ hours (I needed 3 diffuse bounces to reach the floor area under the bed); the rendering time took 5 hours. The reason for 5-hour render time is noise elimination. This method uses no fill light at all, requiring high sampling quality to eliminate shadow noise.
Another disadvantage is artistic control. Controlling image contrast with lighting alone is impossible; post-render color correction is needed.

The other alternative is using an ambient light. You can read about this method as explained by Zap Anderson on his blog. The ambient light is an omni light with Ambient Occlusion projection map.
This method renders much faster. The ambient light helps to (1) eliminate the need for Final Gather diffuse bounce (I used Final Gather with 0 diffuse bounce) as well as (2) minimize the visibility of shadow noise from the key lights (the window lights).
Finally, this method allows more artistic control. By setting different intensity for key light and ambient light, I could control image contrast even at rendering stage.