• Cockleburs (adapted to the latitude of Michigan) will flower only if they have been kept in the dark for at least 8.5 hours — the critical period. (A and B).
• Interruption of an otherwise long night by light — red (660 nm) rays are particularly effective — prevents flowering. (C) unless
• it is followed by irradiation with far red (730 nm) light (D). See spectrum of electromagnetic radiation.
• An intense exposure to far red light at the start of the night reduces the dark requirement by 2 hours (E).

• Phytochrome is a homodimer: two identical protein molecules each conjugated to a light-absorbing molecule (compare rhodopsin).
• Plants make 5 phytochromes: PhyA, PhyB, as well as C, D, and E.
• There is some redundancy in function of the different phytochromes, but there also seem to be functions that are unique to one or another. The phytochromes also differ in their absorption spectrum; that is, which wavelengths (e.g., red vs. far-red) they absorb best.
• Phytochromes exist in two interconvertible forms
  • PR because it absorbs red (R; 660 nm) light;
  • PFR because it absorbs far red (FR; 730 nm) light.
• These are the relationships:
  • Absorption of red light by PR converts it into PFR.
  • Absorption of far red light by PFR converts it into PR.
  • In the dark, PFR spontaneously converts back to PR.

squiggly said:

As a matter of chemistry--often times species are selective as to the wavelength of light they can absorb. Infared light causes most covalent bonds to vibrate--but there are some caveats.

The absorption in different bands of light has peaks and valleys--this is also true for UV and vis spec light. In vis spec, we perceive this as color, wavelengths which aren't readily absorbed are reflected back to us. So something absorbing heavily in the red spectrum will appear green (opposite on the color wheel from red). Hence chlorophyll.

In the UV/IR spec we can perceive this through instrumentation.

An IR spectrophotometer measures the vibration/disruption in energy caused by a sample, allowing us to classify chemicals based on functional group. Different wavelengths will produce different results.

In UV detectors (such as in HPLC) analytes will absorb light and the light not transmitted through the sample comes across as a reading. Different analytes have peak absorption in different wavelengths and it is important to consider this when calibrating the detector--sometimes this requires special tricks. The same is true for the IR application, different compounds will absorb IR light of different wavelengths better or worse based on their properties.

For most of these reactions what is happening is a photon is either knocking an electron out of its orbital--or it is promoting it to a higher energy orbital on an atom. Both of these require specific energy levels/wavelengths to achieve.

What I'm trying to say is that pushing higher into the IR band might not necessarily be better. In fact it may do nothing. (Edit: Turns out going much past the optimum level ~710-740nm would be negative according to the below document.)

Hope this helps.

Edit:

Did some digging and found a document that I think will be quite useful in explaining all of this--Near page bottom is a wealth of info on controlling stem length with pr/pfr ratio.

About halfway down the page you will see graphs depicting absorptions in different wavelengths--these are showing different responses in the plants, but if you plot an absorption spectrum for a single molecule it looks almost identical. There is a large amount of biochemistry info on the page such as the mechanism of the protein, it different domains, its regulator pathways, etc. Alot of that is probably redundant for this application but pretty cool anyway if the language isn't a barrier for you.

http://plantphys.info/plant_physiology/phytochrome.shtml

Click to expand...

click80 said:

very concise understandable post...wish i would have had you for chem 1a...might have passed...lol

Click to expand...

squiggly said:

Thanks :)

I'm actually working on getting a cannabis chemistry compendium together for posting here at the farm. Hopefully it will be sticky worthy and can answer alot of people's questions before they're asked.

Chemistry is my passion, and I'd like nothing more than to interest others in it--or help them solve problems with it.

Click to expand...

growlights said:

I have been developing discrete spectrum grow lights to trigger Phytochrome state changes and all the lights one needs for a PAD systems as well.

Click to expand...

Dr.Trichome said:

very way cool thread.
but it kind of dropped off before we heard how well it works.
Prime, dex, desert. . . .
Love to hear some results, as this Is really interesting

Click to expand...

Desertboy said:

on your site you say
"Wavelength: FAR RED 660nm and 690nm Super LEDs" which is wrong

Where as wiki says
"Far-red light is light at the extreme red end of the visible spectrum, between red and infra-red light. Usually regarded as the region between 710 and 850 nm wavelength, it is dimly visible to some eyes. It is largely reflected or transmitted by plants because of the absorbance spectrum of chlorophyll, and it is perceived by the plant photoreceptor phytochrome. However, some organisms can use it as a source of energy in photosynthesis.[1][2] Far-red light also is used for vision by certain organismsou read that, I cannot find the ty such as some species of deep-sea fishes." from
http://en.wikipedia.org/wiki/Far-red

"In the case of phytochrome the ground state is Pr, the r indicating that it absorbs red light particularly strongly. The absorbance maximum is a sharp peak 650–670 nm, so concentrated phytochrome solutions look turquoise-blue to the human eye. But once a red photon has been absorbed, the pigment undergoes a rapid conformational change to form the Pfr state. Here fr indicates that now not red but far-red (also called "near infra-red"; 705–740 nm) is preferentially absorbed. This shift in absorbance is apparent to the human eye as a slightly more greenish colour. When Pfr absorbs far-red light it is converted back to Pr. Hence, red light makes Pfr, far-red light makes Pr. In plants at least Pfr is the physiologically active or "signalling" state."

http://en.wikipedia.org/wiki/Phytochrome

650-670 is peak nm for waking the plant up

705-740 peak nm for putting plant to sleep

Click to expand...