Carpaint only contains presets because it’s based on measured data (see http://www.mpi-inf.mpg.de/~guenther/carpaint/index.html). There’s also a “Custom” (used to be a blank line in luxblend < RC5 but has been made more obvious in the latest RC). If you understand the parameters (see link to the paper) then you can enter your
own values and get whatever values you want. It’s basically a diffuse layer with two specular ones on top and a clear coat layer on top of that again.
Remember that Lux is a physically based renderer and it might be better to try
to think like a photographer when using it, and not like a “traditional” scanline CG artist.
All materials and settings used in lux is “real world” derived, while most of Blenders
renderer is based on quick approximations with focus on artist convenience (render passes, layers, objects that don’t cast or receive shadows etc etc)
There are pros and cons of each one and any CG artist should try to learn both
techniques (and also photography IMO) - in Blender you will have to invest much
more time and effort in achieving true “photorealistic” results because of all the “quick
and dirty” assumptions and simplifactions made by the internal renderer - and a lot of effects need to be faked or added post-pro.
In lux it’s much harder to get the same artistic “freedom” because it’s limited to whats physically plausible - on the other hand, it’s much easier to get photorealistic results if you approach it like a real photographer would.
Unfortunately that entails having to learn the lingo of physical materials and lighting terms, but it’s worth learning IMO; it will give you more options in your artistic toolkit, and make it easier to communicate with non-CG artists and designers.
Wow, I seem to be long winded today Anyway, the point is I don’t think it’s a good idea - fundamentally - to try to “map” blender internal techniques to Lux, but rather
think like a real photographer would; with an understanding of “real” material properties and lighting instead.