I haven’t started making scripts for Porter yet (still waiting for the steamy version), but I’m pre-emptively interested in this one too.
What you are normally looking for the light knob is not LVAR, but you want to know what light potentiometer it is. Actual script would be something like (AAO):
(A:LIGHT·POTENTIOMETER:1, Percent) 10 + 100 min 1 (>K:LIGHT_POTENTIOMETER_INC)
(A:LIGHT·POTENTIOMETER:2, Percent) 10 + 100 min 2 (>K:LIGHT_POTENTIOMETER_INC)
Etc. those are increase light potentiometer 1 or 2 by 10 percent up 100% respectively. Sometimes you need to add 1 (>K:PANEL_LIGHTS_SET) or 1 (>K:GLARESHIELD_LIGHTS_SET) etc. to the script too.
Unfortunately the light potentiometer is often not available through the dev mode and you need to either guess it or look at airplane code, systems.cfg is my go-to for this, though sometimes you need to look at model/airplanename_interior.xml. Unfortunately I don’t have either of those available since I have the marketplace version and those files are encrypted, hence why I’m interested.