In X-Plane 11, the new lighting and material model, which uses Physically Based Rendering, is always on. Even at the lowest settings!
In X-Plane 9, 10 and 11, we have introduced major changes to the lighting model at new versions, so we could have a reasonably stable lighting environment for the life of the product. Each time we introduce these new features, we need to decide if they are always on or optional.
My preference is "always on" when possible; having these kinds of big features be optional makes life difficult for authors, who can't be sure how their content will look in the simulator.
When we introduced HDR with global night lighting in X-Plane 10, it was (and still is) an optional feature. This is because deferred rendering mode uses a lot of GPU memory bandwidth, and many Intel GPUs simply can't handle this rendering load. Because Intel GPUs represent a non-trivial percent of our install base, we can't make features that don't run on Intel hardware mandatory. Thus HDR remains optional. (We checked this in X-Plane 11 and we still can't make HDR mandatory. Maybe in X-Plane 12. 🙂
The new lighting model ties three features together: (improved) volumetric fog, atmospheric scattering, and physically based lighting equations with the new material model. These features are always on in X-Plane 11, and this makes life easier for our artists; the lighting environment is always the same no matter what the settings.*
With physically based rendering, we support lower end systems by reducing the quality of the effects, rather than by removing the effect entirely. Most of the cost of PBR is in calculating the processed reflection textures to make PBR work. At low settings we can reduce the texture resolution and remove detail.
This tuning is still in progress; testers who were in our private beta program know this because they saw significantly worse framerate in beta 1 than in the public beta. A lot of this performance tuning is finding ways to make the lower end settings do less work than the high-end settings.
I'll post more next week on how to use the new PBR rendering, but for now this is posted and a good start.
* It makes life easier for me too by greatly reducing the number of combinations to debug.