Correct. It’s pointless to run the 730 while running your other LEDs. 680-700 for Emerson effect and you can run those during lights on. Then after lights out the 730 for a couple minutes to work the phytochromes.
Wrong! The Emerson effect is the strongest at the wavelengths you've mentioned but it also occurs when you use 660 and 730nm or other combi's. And warm white light already has a lot of deep red in it. This means that the Emerson effect also occurs when you add only 730nm.
Think on CRI80 vs. CRI90... CRI90 is up to a week faster and most of the time without loss in yield even though it has less PAR. Thats because of twice as much far-red, mate.
In mother natur the plants get much more far-red like you think. In strong sunlight the red:far red ratio is ~55:45% and the phytochromes are constantly switched from its active to its inactive state(Phy-red to Phy-far-red and back to Phy-red), on and off, on and off, all day long!
Indoors without far-red the plants only get deep red and all the phytochromes are switched to Phy-far red(inactive state) and they only switch them back to it's active state at night. This cause and imbalance between photosynthesis system I and II. So in the end far-red in not driving photosynthesis but it evens out the two PS systems and this wqy it cause more efficient photosynthesis.
yes some people run 670 with 720 for emerson effect at a certain ratio. Im not sure what ratio it is because im only playing around with far red right now. Emerson effect is best used with ppf of max 500-600 (somewhere around there). Any higher above that (im at 800ppf) and emerson effect isnt as effective from what ive read. Im sure alot of growers here are well above me even.
The emerson effect occurs always even at higher light levels but the effect is stronger in low light conditions. So even with 1000μMol/s there is a small effect. But far-red has other benefits like you can read in the science paper below. I'm pretty sure all these effects work hand in hand and when you remove something the plant has to compensate it as far as possible. If its impossible, like with missing far-red, it will cause an imbalance.
There is only one rule when using far-red over the day. It has to be less than red. With a red: far red ratio of 45:55% you would cause SAS(shade avoidance syndrome) cause the plant would "think" she would stand in the shade. In shade there is always more far-red..
In the science paper below they have used up to 90μMol/s/m² additional far-red with measurable results. I've currently ~50μMol/s/m² of far-red in my tent(~850μMol/s/m² total at 14"), one half is coming from 8pcs CRI90 COB's the other half from 10w extra far-red and it works very well without causing much more stretch. They stretch out a little earlier, yes, but final end height is about the same... Same like under CRI90..