Just a little question, from what I see, HDRI are used most of the time alone to light the scene but are there situations where you use a HDRI + some lights in the scene ? Any particular exemple where that could be handy ?
Hi nabro - yes there are many situations where HDRI + lamps are used together. For example I recently rendered a kitchen scene where I used an HDRI to provide general "outside" light while using lamps inside the kitchen to represent artificial light (can lights in the ceiling and under-cabinet lights)
An HDRI alone can be used to light scenes by themselves, especially naturalistic outdoor lighting. However rarely do I use lamps by themselves without an HDRI for at least some subtle environment contribution. I mean, when in reality is there *only* artificial light with zero environment? Pretty rare. I can only thing of a deep cave, deep in the ocean, or an exaggerated studio light setup.
Generally I like to start with HDRI alone since it does so much by itself, whether naturalistic outdoor or a studio HDRI. It's also very easy to manipulate. If that's not 100% satisfactory I'll start adding lamp objects.
Hope that helps.