I'm trying to understand how modern window films or coating (so-called "Low-E" coatings) can improve the "R" value of the window just by reflecting internal room radiant energy (presumably long-wave IR or black-body radiation) back into the room.
I presume that a room containing air and various objects at "room temperature" will emit a certain amount of IR and some percentage of that will pass through the window aperture, but glass with a low-e coating will reflect some of that IR back into the room.
My "gut" (or rather, my hand - on a cold window surface in the winter) tells me that the window does an excellent job of presenting a cold surface to the air circulating in the room, and a lot of heat is carried out of the room through thermal transfer, which does not involve the low-e coating.
Since I don't have a good "feel" for how energetic or intense the long-wave ambient room IR is, I really can't appreciate what the low-e coating is doing in terms of improving the window's total insulative property. Nor can I get some sort of idea as to what my primary question is here - which is to get a rough idea if the ambient room IR amounts to 5% or 50% of the total heat energy passing through a window in the winter.
Bonus question: Does the air in the room emit IR (enough to be of any significance) or would it be just the more dense materials / objects / surfaces?