Night Hacker gave you a lot of information there, just as a side note (and I quoted
Night Hacker because he may not have known this) The Exposure Compensation button he mentions is a post render process not actually built into the rendering engine. This is even though it might appear to be built-in to the iray engine. It is generally better practice to add more light to the scene pre-render than post-render. If that means you up the value of each light source and up the intensity of the HDRI if you are using one, then do that first, before hitting that exposure compensation button.
One other note, the DAZ exposure compensation algorithm is not as good as Blender, GIMP, or Photoshop. Jus keep that in mind if you decide to ever post-process your images.
Honestly, I do not know why the DAZ developers made the exposure compensation a post-render process, maybe it was easier to implement. But that is only a wild ass guess.
In your image above, I might have added a diffuse fill light from slightly to the left of the model (model's left, not your left) that would open up the face a bit and a better exposure overall.