Would be fun to pick your brain a bit on this as that information is all (somewhat?) new to me. I didn't know about the outlets mostly being wired as 12. Would that make them all 20amp outlets instead of 15amp? Any idea of why this change happened? Is it just to allow for more power across all the outlets in a home? Less home runs to be used? It seems like a strange change to make considering how many homes are mostly 15amp circuits.
Not sure I've ever wired any lighting with anything but 14/2. Always have had a hot/neutral/ground at those locations. The 12/2 just seems weird to me, but that is the size I pull to a lot of locations.
I think the new wire ga requirements are for instantaneous loads, but ya know, they make the rules, we/electricians need to follow. I got a serious kick to the nads a bit over a year ago when I needed Romex and couldn't find what I KNEW I had- one 15' piece cost more than $1/foot. WTF????????????????????????????????? They also know people overload outlet circuits, so....electric space heaters, toasters, window/portableAC, etc with power strips and six way outlets- anything to cause a fire and claim ignorance, I suppose.
Got the thing wired and I doubt it was more than an hour until I found ALL of the Romex that, as I wrote, I HAD!.
Lighting doesn't need 12ga, especially now that most bulbs aren't incandescent.