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~A Cultural Healing and Life Compilation and Writing.

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  1. Advanced Section I - Understanding light, photosynthesis and how to select grow lighting
  2. Advanced Section II - Lighting & Reflector Section
  3. Advanced Section III - Plant Growth and Light
  4. Advanced Section IIII - Understanding Light Measurements
  5. Advanced Section IV - Advanced Lighting Information and formulas.
  6. Indoor Garden Environment

 

Light Section III

- Advanced Plant Growth and Light

 

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ttp://forever-green-indoors.myshopify.com/blogs/news

Plant growth is driven by three processes which are responsive to light:

  • Photosynthesis (metabolism)
  • Photomorphogenesis (form development)
  • Photoperiodism (daylength reaction)

 

Photosynthesis

The most important of these processes is the photosynthesis: the basis for plant growth and development. More simply, it is a process that all plants use, to collect the energy from the sunlight. The plants store the collected energy as carbohydrates, so that the sunlight basically serves as food for the plant. The light is absorbed with the aid of the pigment chlorophyll.

The two most important chlorophylls are chlorophyll A and chlorophyll B. Chlorophyll A absorbs the light in the blue and red wavelengths. Green and far-red light however, are little or not absorbed. Chlorophyll B uses a similar range, with absorption peaks closer to the blue end of the spectrum. So right there if we are custom designing a light spectrum we want to hit blue and red.

 

Absorption Spectrum Chlorophyll A, B and Beta-Carotene

medium.5aa33d15c6bd3_ChlorophyllBetaCaro

 

 

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The "action spectrum" is the sensitivity curve of the light on plant's photosynthesis. In order to make accurate statements about the light absorption of different pigments, scientists undertook a complex measurement process using a spectrophotometer where each wavelength was tested for the specific absorption rate. The result of the activity of main pigments and auxiliary pigments is shown graphically in the action spectrum.

 

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action spectrum graph

Comparing the action spectrum with the corresponding absorption spectrum of chlorophyll you will note that they do not match. In fact, the absorption spectrum leads to the conclusion that photosynthesis is primarily driven by blue and red light and we believe this is true in cannabis photosynthetic response - depending on the phase of plant growth.

 

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A plant will benefit to some degree from all the light wavelengths or spectra that the eye sees, but they respond best to spectral regions at the outer edges of peak human vision. If the artificial light spectrum is narrowly emitted, or missing altogether, then the plants will not develop to the fullest leafy vegetative, or bulky flowering stages that natural sunlight would have provided.

 

Photomorphogenesis (form development)

  • Young plants such as newly rooted clones prefer the Action Spectrum.
    • In fact too much light intensity on the red wavelengths is harmful to young cannabis plants.

On the other hand as plants grow in the 20-24 hour vegetative stage they move from only being able to handle the Action Spectrum, to very much being driven by the Absorption Spectrum. And this makes sense because this is when plants are growing like crazy, absorbing the light to create chlorophyll A & B.

 

Photoperiodism (daylength reaction)

Now what is really fascinating is that when it is time to turn the lights down to a 12 hour day

  • which will induce the reproductive or flower phase
    • then we've found that the plants are firmly desirous of the spectrum weighted to chlorophyll A and in fact prefer much more red wavelengths.
  • They produce flowers as a means to pass on their genetic heritage.

Red light seems to trigger a response in plants that they need to stretch to out compete their neighbors. And to produce the largest flowers possible.  Cannabis in the flowering stage of growth will be looking for between 800-1000 umol. (par)

 

 

Union Break!

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Click and take a break, Union rules, what you gonna do?  Take a break that's what your gonna do.

 

 

 

 

Light and Photosynthesis

https://fluence.science/science/photomorphogenesis-guide/

  • Light causes a biochemical processes in plants.
  • Some of these processes regulate key stages of plant development, such as germination and flowering
  • They depend strongly on the spectrum of the light and in some cases, also on the timing, periodicity and the overall exposure.
    • This is called fluence, and is measured in micromoles of photons per square meter of surface.
      • Lowest is star light
      • Highest is direct sun.

In terms of spectrum dependence, by far the best understood today are the processes controlled by red and far red light. For the purposes of this discussion, red (R) is the spectral region around 660 nm and far red (FR) – that around 730 nm. In order to better understand the significance of these two spectral regions, it is necessary to also consider the chemical mediator of the corresponding responses, called phytochrome.

  • Phytochrome is a blue protein pigment which exists in two forms – a red light absorbing one (Pr) and a far red absorbing one (Pfr).
    • Each of them converts into the other upon absorbing the corresponding light until an equilibrium is established, with the relative amount of each form depending primarily on the ratio of R to FR light in the spectrum.
    • In addition, the Pfr form will slowly revert spontaneously into the Pr form if left in complete darkness.

The prevalence of one or the other form (which depends on the R/FR spectral ratio as well as the dark photoperiod) in a plant can stimulate or inhibit a number of developmental processes such as

  • germination,
  • leaf unrolling,
  • chlorophyll formation,
  • stem elongation and
  • flowering.

This is generally referred to as photomorphogenesis

  • For example, some plant seeds will not germinate unless they are exposed to red light.
  • Also, plants growing in the shade of other plants will become taller than they would in full daylight.
    • The reason is that light filtered by plant leaves becomes depleted in red light and enriched in far red light.

This shifts the phytochrome photo equilibrium towards the Pr form and triggers the shade avoidance response of stem elongation, which increases the chances for the plant to reach the direct daylight.  (Stretching)

Although the R:FR ratio in daylight can vary over the course of the day and will become somewhat lower at sunset,

  • the length of the dark period is even more influential on the phytochrome photo equilibrium since the Pfr molecules in a plant will start undergoing the dark reversion process at nightfall.
    • The longer the night, the relatively higher the amount of the Pr form will become. In turn, this amount is strongly involved in the control of flowering for quite a few plants.
  • There are long-day plants (which require short nights to flower), short-day plants (requiring long nights) and day-neutral plants which have no specific requirement for the photoperiod.
  • This dependence on the photoperiod is referred to as photoperiodism.
    • Different light treatment is needed on a case by case basis, especially when one needs to induce or delay flowering.
    • Lights on for 12 hours and off for 12 hours for traditional flower times.

In artificial horticulture lighting, there is a number of choices – especially when it comes to using LED lights, which can have any desired ratio of R/FR light.

  • Since FR light is not photosynthetically active, its use in horticulture lighting is often limited for reasons of energy efficiency.
    • A good energy-saving strategy is to use one set of lights for growth and another – for (flower) photoperiod control when necessary.
  • The former set can have a very high R/FR ratio (as high as several thousands) with no ill effect for most plants.
  • The latter set can consist of a pure red source (e.g. 660 nm LEDs), a pure far red source (e.g. 730 nm LEDs), or a combination of both.
  • Since phytochrome response is in the low fluence range, the number of fixtures needed for (flower) photoperiod control may be much smaller than that of fixtures needed for growth.
  • In addition, the operating time needed for photoperiod control can be much shorter, such as only minutes at a time.

For example, flowering of a long-day plant may be induced by night interruption, using a series of short flashes of red light with photon flux levels as low as a few micromoles/m2s.

  • (Lights with a high R/FR ratio installed for growing purposes may be used instead with the same effect.)

Short-day plants may be induced to flower by a single flash with pure FR light at the very beginning of the dark photoperiod, after turning off all other lights.

  • This effectively adds a couple of hours to the dark period for the purpose of flowering, which can be used to extend the light period for growth and optimize plant yields overall as a result.
    • Switching the above methods for plants with opposite photoperiod requirements would delay flowering, which may also be desired sometimes (e.g. to provide the best quality flowers on schedule for certain holidays).                    

It should be noted that although the R/FR ratio is often used to describe light spectra, it affects the phytochrome photo equilibrium only up to a point, and not always in a directly proportional way.

  • The reason lies in the overlap between the absorption spectra of Pr and Pfr.
    • As a result of this overlap, the highest concentration of Pfr does not exceed about 80% of the total phytochrome concentration even under pure red light, while the lowest concentration of Pfr can be almost 0% for the pure FR region.
  • Light sources containing red light and no appreciable content of far red light maintain equilibrium values for Pfr in the 70 to 80% range, meaning that they behave similarly to pure red light in this respect. Those have no ill effect on most plants;
    • however, some FR light may have to be added to the growth spectrum for any exceptions requiring continuously lower Pfr concentrations.
      • If necessary, it is possible to custom design light spectra targeting any Pfr equilibrium value within the entire physically obtainable range, after performing calculations of the phytochrome photo equilibrium under different relevant wavelengths.
      • Since this can reduce the photosynthetic efficiency of the light (thereby increasing the overall cost of lighting), it should always be done judiciously.

 

medium.spectrum.jpg.e9d2f5fb05a9bc07ba46

 

 

:nerd:  If you been reading a bit, take a union break.

 

 

The blue spectral region is also important for a variety of plant responses such as

  • suppression of stem elongation,
  • phototropism (bending towards the light source),
  • chloroplast movement within cells,
  • stomatal opening and
  • activation of gene expression, to name a few.

Some of these are morphogenic and others aren’t. The mediator molecules can be cryptochromes, phototropins etc., unlike the phytochrome mediated responses reviewed earlier.

  • However, blue light responses are not reversible under far red light, which allows for their straightforward experimental distinction from the red light ones.

Stomatal opening and height control are of particular relevance to horticulture lighting.

  • A much too low content of blue light in the growth spectrum (e.g. less than 10% of the total photon flux) can lead to leaf edema (swelling of the leaves) and developmental problems in some plants.

The absolute content of blue light has a progressively stronger effect for plant height reduction.

  • This may be desirable in some cases (e.g. to produce more compact seedlings and reduce transportation costs) but generally leads to lower photosynthetic efficiency of the light with respect to energy consumption.
    • A high relative content of blue light reduces the plant leaf area and may be undesirable for that reason.

Near UV light has an effect similar to blue light, with further reduced photosynthetic efficiency, especially below 400 nm (although the other effects may be stronger by comparison).

  • It also affects the biosynthesis of compounds responsible for the flavor of certain fruits, as well as that of other compounds which are not directly produced by photosynthesis alone.
  • Whenever the use of near UV light is necessary to control a corresponding sensory mechanism or the production of a specific molecule of interest by the plant, an overall efficiency trade-off may have to be reached, similarly to that for the use of far red light.

Finally, the control effects of green light are generally opposite to those of red and blue light, and have been considered as “a signal to slow down or stop”.

  • Another way to look at them is as the means to achieve a balance between spectral actions and counteractions, needed to adjust plant development and growth.
  • The phytochrome and cryptochrome molecules mentioned earlier are also responsive to green light – even though to a significantly lesser extent than to red or blue light, correspondingly.
  • So far, all efforts by researchers to find photoreceptors responding primarily to green light have given no definitive results.
  • The addition of green light into the growth spectrum has been demonstrated to be beneficial for the growth of certain leafy vegetables.

In summary, only a few plant species will grow best under pure red light, although the latter has the highest possible photosynthetic efficiency. As a minimum, a horticulture light spectrum should also contain some amount of blue light. Green, far red and near UV spectral components may have to be added for optimal plant development. The photoperiod length can be critical for flowering, and pure red or far red light sources may also be used for flowering control in an energy-efficient manner.

 

 

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You earned for finishing Section III

 

 

Click for next - Advanced Section IIII - Understanding Light Measurements

http://culturalhealingandlife.com.www413.your-server.de/index.php?/topic/9-section-iiii-understanding-light-measurements/

 

 

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~ Hempyfan, A proud HD writing

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