Hmm but its been at least 10 years that we have far red LED i think that if in 10 years no one was able to prove an increase in terpene or any real advantage for the cannabis industry i think its not really making much a difference for cannabis, lettuce totally worth it, cannabis not so much, as you say no study prove any real advantage, so its a bit like giving mineral water to your plant and hope it make a positive impact even thought no study has ever claimed a proved benefit.
Migro dude who made some test on far red and havent found any real advantage to it in this video
Also the guy from apogee instrument made a video on far red and show that it does have benefit... for leafy plants.
The problem though is that we have not been able to study cannabis "legally" for very long, even Bruce Bugbee (the apogee guy) is one of the leading light researching scientists, and he only does studies on hemp because the universities are not allowed to study cannabis (many times due to funding, local laws..etc). The research just isn't there yet on cannabis and Far Red lighting... Some things are known and can be used beneficially as I will point out below, but some things just need more research...
You can't just say "far red IS/IS NOT beneficial" as a blanket general statement... because like I mentioned above, there are MANY aspects to evaluating plant lighting and many uses for Far Red light and plants...... for example... without a doubt.. SOME far red light is absolutely necessary for the emerson effect. in this case, Far red is absolutely important and useful...
Emerson Effect: some far red is absolutely needed for the best possible photosynthetic efficiency... the ratio of far red though is dependant on other factors because the higher the ratio of Red/Far red, the less stretch you will get, the lower the ratio of Red/Far red then the more stretch you get... the ratio is what is important, but some far red is proven absolutely needed.
If we look at flower/photoperiod manipulation with far red (bloom boosting aka using it for 15 minutes at lights out) to convert the Pr to PFr faster, this absolutely effects the plants flowering cycle, this is fact.. but is this beneficial for cannabis? well depends on how you look at it.. and what is your goal... If you have a commercial grow of 100,000 plants, and cutting a week off a flowering cycle means more profit, less electricity usage, quicker cycles.. etc.. then absolutely using Far Red for flower cycle manipulation would be a benefit...
If you are growing short indica plants and want to add stretch to the plants... then INCREASING the Far Red/Red ratio is absolutely necessary and beneficial..... however, doing this to a stretchy sativa, then it may NOT be beneficial..
We just can't make blanket statements with Far red and cannabis... saying "Far red IS/IS NOT" beneficial...etc" because it can be used different ways, to achieve different results... For some things, it HAS been proven to be able to be used favorably, where other things like "does it increase weight" or "does it increase potency"...these types of questions still need much more research on actual cannabis plants in a controlled study... its not a black/white type question and answer... its much more complex than that...
So really, much more research (on cannabis) needs to be done... we know basics with Far Red, however to answer specific questions on it (does it increase yield)? more specific research is needed to gain useful answers. Just like for years... when LED first came out people used to say Green light is wasted energy, its worthless to plants...etc... just recently about 2 years ago, this was proven wrong, and that Green light is far more important than previously realized.. however it took specific studies to realize this.. up until then, it was just generally assumed plants don't use green light... which we know now is false. Plant lighting is still a very under researched area... especially on cannabis plants.
For example, here is some recent research on cannabis and the "RATIO" of Red to Far red light....
The Effect of Light Spectrum on the Morphology and Cannabinoid Content of Cannabis sativa L. which shows
"Plants under HPS treatment were taller and had more flower dry weight than those under treatments AP673L and NS1. Treatment NS1 had the highest CBG content. Treatments NS1 and AP673L had higher CBD and THC concentrations than the HPS treatment. Results were similar between experiments 1 and 2. Our results show that the plant morphology can be manipulated with the light spectrum. Furthermore, it is possible to affect the accumulation of different cannabinoids to increase the potential of medicinal grade cannabis."
In this study, they prove what is already known about the Ratio of Far Red light to Red light... the more far red, the more stretch... But what they also found was that the cannabinoids ALSO reacted to the different light types.... where both LED lights had higher cannabinoids in them over the HPS light, however the HPS light produced more yield...
The problems though with this study are that the light sources are SO VASTLY DIFFERENT, although the ratio of Far Red IS a factor, its NOT the ONLY factor which could have played into the observations (for instance LED generally has much more blue) and blue light has more energy in it.. therefore blue light "hurts" the plant more than red light so therefore blue/violet/uv light is generally associated with more plant response (SAR) where plants produce more protective "sunscreen" and cannabinoids.. Therefore this experiment is sort of flawed because it doesn't isolate just the Far Red.....
Again, as this experiment shows, there are TOO MANY COMPLEX processes going on to just say "Far red light is bad" or "far red light is beneficial" its way more complex than that.
LOL 
