Render without Lights...(almost)

...it can be done. But also depending on some situations or whatever effect you may be after. In this case, I had the "luck" of using an HDRI which was available from Paul Devebec's Site.
The project (in LNS) at hand was some bar / lounging area. The design was modern and incorporated some sleek lighting fixtures, and lots of glass. And this is one type of project that required to show this concept, and yet set it in a night effect.

This pass is basically using most of the GI settings and environment to light up the place. No lights were place just yet. The supposedly light fixtures were simply made with self-illuminating materials.

After a few adjustments in the materials, I simply used an HDRI in the environment to give it the "colour." And omni lights were just placed at the egg-shaped lamps that were on the tables. It just so happens it turned out quite well, such that I did not have to place any other lights. With a few tweaking in the influence of the HDRI environment, I managed to get to this point where I felt comfortable to proceed in finishing the image in post.

My post-processed image. I simply adjusted the curves, and enhanced the colours by a number of Layers in Photoshop...either by adding photo filters and mixing up with soft light effects and blurring. Other details were also added, such as the wine bottles by the bar and painting some of the specular reflections.
One thing I noted was that it took some time to render this thing. And once, I had it rendered to a very hi-res resolution, splotches and unwanted colour spills became evident (as I think) due to the "low-res" HDRI. It disappeared actually, once I got rid of the HDRI, but of course I lost the coloured effect. So for an upcoming animation, I tried to recreate this coloured effect by adding 3d physical lights in the scene. At least now I had a clear visual reference. And It rendered faster.