The lighting mods make a lot of difference to the amount of light that you have on your sims, but by themselves, they aren't the whole solution.
My advice is to use the most expensive indoor wall lighting and put them everywhere, along with a ceiling light above where the sims are. When I'm in public places, I change the lighting to make sure that I can see the sims and get good photographs of them.
This is by design, but my understanding is that the Gurus are working on improving the lighting. The intention is to allow players to select higher "quality" lights (based on their cost) that will light the entire room, but this doesn't work on its own, which is why you'll want to install one of the lighting mods to make up with the difference.
Be aware that pure white light with a mod installed can be too much, so consider cooling your white light or setting some lights in the room to different colors in order to soften the brightness.
Also, white or light colored walls, floors, and furniture will reflect the natural light (no mods) to make your sims somewhat brighter.