What is the importance of far red light?

Advanced Techniques
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This is not about far red light but about terms used when talking about light.
I thought some may find it helpful.

PAR, PPF, PPFD, and PFD Explained

Summary:
00:40 1960s: Researchers measured radiation only with a pyranometer, which included all shortwave radiation from the sun (280 to 2800 nm), but only a small portion of that (400-700 nm) is used by plants.

01:59 We begin with the first term that evolved - photosynthetically active radiation (PAR). PAR is the light from 400 to 700 nm that is used in photosynthesis. It’s not a measurement or metric, it defines a type of light.

03:05 1970s: A researcher clarifies that 400 to 700 nm is not referring to energy, it’s the number of photons that cause photosynthesis. The next term to evolve is photosynthetic photon flux (PPF).

04:28 Language continuously evolves. As a result, PAR and PPF were used interchangeably when referring to the number of photons that cause photosynthesis.

05:19 PPFD and PPF have been used interchangeably for 50 years; however, these terms continue to evolve. PPF refers to an AMOUNT per TIME. Photosynthetic photon flux density (PPFD) refers to an AMOUNT per AREA per TIME.

07:57 Dr. Bugbee, about three years ago, started using PPFD in his publications after discovering different disciplines use the acronyms differently.

10:20 PAR is still used in common speech, and is used as a more generic term to refer to energy flux or photon flux. PPFD is used for an amount per area per time. PPF is used for the the amount per time.

11:00 The difference of PPF and PPFD further explained. PPFD helps define the intensity of the light over a given area.

13:46 When reading literature, make sure to always check the units. It should always be micromoles per meter squared per second. The older literature used to call that PPF.

CONCLUSION

14:30 There’s a new term emerging that refers to photons beyond PAR - Photon flux density (PFD). Far-red and ultraviolet radiation have been discovered to also cause photosynthesis and effect plant growth. With PFD, we are no longer constrained to 400 to 700 nm. E.g., PFD can mean 300 to 800 nm.

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According to the paper “Photosynthetic response of Cannabis sativa”

At 77 F, rate of photosynthesis increased with increasing PPFD, but this trend peaked with 1500 μmol m-2s-1 PPFD, 86 F, and decreased at higher light intensities.

So there lies our sweet spot.

An interesting note on the action of intercellular Co2 under high levels of light.

A continuous decrease in intercellular CO2 concentration (Ci) and therefore, in the ratio of intercellular CO2 to ambient CO2 concentration (Ci/Ca) was observed with the increase in temperature and PPFD. However, the decrease was less pronounced at light intensities above 1500 μmol m−2s−1.

Optimal Light Intensity – Mammoth Lighting

Fig. 3. Variations in rate of transpiration in C. sativa with varying photosynthetic photon flux densities (PPFD) and temperature conditions.
Fig. 3. Variations in rate of transpiration in C. sativa with varying photosynthetic photon flux densities (PPFD) and temperature conditions.588×572 4.98 KB

Fig. 2. Variations in stomatal conductance in C. sativa with varying photosynthetic photon flux densities (PPFD) and temperature conditions.
Fig. 2. Variations in stomatal conductance in C. sativa with varying photosynthetic photon flux densities (PPFD) and temperature conditions.620×582 4.99 KB

Fig. 1. A. Variations in net photosynthesis in C. sativa with varying photosynthetic photon flux densities (PPFD) and temperature conditions. B. The temperature dependence of Dark respiration in Cannabis sativa.
Fig. 1. A. Variations in net photosynthesis in C. sativa with varying photosynthetic photon flux densities (PPFD) and temperature conditions. B. The temperature dependence of Dark respiration in Cannabis sativa.650×794 5.26 KB

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43

This study seems to show an increase in yield beyond 1500 u-mols


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The potency of total terpenes, myrcene, and limonene increased linearly from 8.85 to 12.7, 2.51 to 4.90, and 1.05 to 1.60 mg·g−1 inflorescence DW (i.e., 1.4, 2.0, and 1.5 times higher), respectively, as APPFD increased from 120 to 1,800 μmol·m−2·s−1. There were no APPFD effects on the potency of the other individual terpenes.

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44

More from my buddy Bruce.

My notes:

Blue photons

  1. can keep plants short and add to flavors.
  2. Not as efficient as red photons.
  3. Enhance red pigments in plants. (red pigments are formed as photo protectants)
  4. High energy
  5. Quickly absorbed

Green photons

  1. work well for people to see.
  2. Helps with canopy penetration
  3. do not use in the dark cycle- plants do see green light, as well as other colors

Red photons are

  1. the most photosynthetically and electrically efficient.
  2. lower energy longer wave length.
  3. Quickly absorbed
  4. is responsible for light bleaching, high fractions of red light and plant don’t make photo protective pigments.

Far red photons

  1. increase stem elongation.

Rapid changes in light matter but not as much as we think.

Plants adapt to new light levels within 1-2 days.

Bruce says 1000-1200 u mols per second, is optimal for cannabis.

Yield increased even beyond 1600 u mols per second.

Double the light, double the water usage.

10% blue is all plants need, more than that may keep plants too short.

Formula for LED light fixture comparison.

  1. U mols out
  2. watts in
  3. price per fixture.

Multiply light sources penetrate the canopy deeper.

This is why big rooms get more weight per light.

A good reason not to prune leaves.

Old lower leaves automatically translocate nutrients and carbon to younger leaves.

A good reason to prune leaves is for airflow, pest prevention, ect.

Here is a link to a Light meter for your phone, dunno if it is any good???
Thought some may find it useful.

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45

I am unsure if 660nm is considered far red. Its just one of the small 6.5watt 4LED puck I got off Amazon. I see the same company has a 730nm far red for sale. So I doubt mine is the far red.

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Yep, 730nm for the win.

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This is the one I’m going to test. based on calculations I’ve done this handmade creature made by me emits 28% B, 22% G, 38% R and 12% far R. The plan is 3 of them reaching 2000 umol/s in 1.26 m2. I will report results soon.

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@immygod
How very cool, keep us posted on how this works for ya. :star_struck:

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I think its needed. Even just for a greater awareness… it sucks that we are ruining the resources.

Damn Humans (ie: monsanto and co)

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Screenshot_2023-03-24-17-45-20
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here is the effects of 28% B, 22% G, 38 % G, 12% far-R, 27-29° C, 35-40% RH, 400-1500 ppm CO2, day 17 from seed

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Nicely Done. Thats my first Holy-Shit of the day!
Appreciate the info and that Light looks wild. Good Luck

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Did you have any luck?