if you go to your local petco you can buy a bulb for every kelvin you can imagine.
emulating nature will most always be the best deal. you make a good point, where in the world does ANY organism receive that much time under the sun? no where.
as far as kelvins(or nm), the best way to do it, if money were no option, and if you could find ALL of the proper bulbs, i would try to find bulbs between 1800-3000, i would go with 5 of these, at 1000 lumen apiece. try to get one 1800, a 2000, a 2500, 2700, 3000. (you get the idea.) you really would see major benefit if you could get all of these spectrums together.
in addition to the lower end of the kelvins, you should also try to find 1000 lumen bulbs between 5000-8000, pick 5 bulbs at increments similar to the other ones i just gave as an example.
ideally you should be shooting for 10,000 to 15,000 total lumens from the mixed spectrum, excluding green light which is about 4000k.
on a super sunny summer day, the sun spits out between 10,000 and 25,000 lumens per sq ft depending on ozone, cloud coverage, smog, and a few others things.
more lumens, will make your plants produce more, just as long as the heat is kept in check.
so a recap, mix the spectrums as much as possible, exclude green light~3500k-4500k, shoot for 10,000 lumen or more, if you can. you will still get growth with less lumen, just ultra, ultra slow.