Here’s a video you may like, this is sound info.
This should give you a good base of understanding of Far red light.
How Does Red And Far-Red Light Impact Crops?
I would like you to meet my main man Bruce!
There are other uses for red and far-red light in terms of photoperiodism and flowering response.
Research “night break” and “end-of-day” far-red light treatments, as well as the other topics.
Cannabis flowers due to changes in the night length (mainly), it senses the changing dark hours per day (diurnal period) using far-red light and red light. As well as Cannabis can flower due to age for some genotypes in unfavorable lighting conditions (like if the night isn’t long enough).
Far-red light is used for these things by growing plants, including Cannabis:
photosynthesis
photoperiodism
flowering induction (for some species, such as Cannabis sativa L.)
photomorphgensis
phototropism
Far-red isn’t something you would want to add to your spectrum normally, unless for very special use-cases (not photosynthesis)."
"FAR-RED:
In terms of not adding extra far-red I was referring to white light. If you have a LED array, you need to add far-red if it’s not already provided by the LEDs.
Read up on “phytochrome photoequilibrium,” “phytochrome,” “photoperiodism,” “red far-red ratio,” “shade avoidance reaction,” and “Emerson effect” to get a better understanding about use of far-red light by plants.
We want a red:far-red ratio of around 1 to less than 4 for indoor lighting. Sunlight is 1.05 to about 1.2 in the day, and about 0.6 to 0.8 at sunrise and sunset.
For PPE (aka PPS, “phytochrome photoequilibrium”) we want about 0.8 to 0.9, sunlight is about 0.5 to 0.72, except at sunrise and sunset when it’s much lower."
For more info on this topic, Google around for knna’s past writings on this topic of using far-red and red light to affect plant photoperiodism (for example, shorter nights to flower) and photomorphgensis; he has the best writing on this for Cannabis.
What I am referring to termed “shade avoidance reaction.”
It just means when there’s too much far-red light (725 to 735 nm; peak is 730 nm) relative to red light (655 to 665 nm; peak is 660 nm) the plant thinks it’s shaded, so it grows more (stretches) to try to get above the shade.
There are few research papers and studies you may want to review if you want more info about these topics. “End-of-day treatment” is also a common use for far-red LEDs:
Phytochrome allows plants to sense the color of light.
A higher proportion of FR light allows plants to detect when they are shaded.
Plants adapted for growth in full sun will display greater stem elongation when they are transferred to shade. They also develop smaller leaves and less branching. This change is due to greater proportion of Pr to Pfr.
