I posted this on another forum thought I'd share with you guys.Phytochrome is a photoreceptor, a pigment that plants use to detect light. It is sensitive to light in the red and far-red region of the visible spectrum. Many flowering plants use it to regulate the time of flowering based on the length of day and night (photoperiodism) and to set circadian rhythms. It also regulates other responses including the germination of seeds, elongation of seedlings, the size, shape and number of leaves, the synthesis of chlorophyll, and the straightening of the epicotyl or hypocotyl hook of dicot seedlings. It is found in the leaves of most plants.
Biochemically, phytochrome is a protein with a bilin chromophore.
Phytochrome has been found in most plants including all higher plants; very similar molecules have been found in several bacteria. A fragment of a bacterial phytochrome now has a solved three-dimensional protein structure.Other plant photoreceptors include cryptochromes and phototropins, which are sensitive to light in the blue and ultra-violet regions of the spectrum.
http://en.wikipedia.org/wiki/Phytochromecircadian
rhythms is just how a plant times a single day.This is the really interesting bitPhytochromes are characterised by a red/far-red photochromicity. Photochromic pigments change their "colour" (spectral absorbance properties) upon light absorption. 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 650670 nm, so concentrated phytochrome solutions look turquoise-blue to the human eye.
This is the bit that interests me the most
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"; 705740 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.
Using a light in the 650-670nm range will put the phytochrome into it's signalling state (or for our particular plant it will keep the plant in veg.) Even if you gave a plant 12/12 if you had a 660nm light source of suitable intensity the plant would stay in veg mode. The intensity of light needed to keep in veg especially since the change of state from Pr to Pfr is near instantaneous means that pulsing a low wattage 660nm light will extend the day for minimal electricity costs. How useful to a ganja grower is debatable but you could start plants in a conservatory in March and use this to extend the day. normal cfl's contain enough 660nm to work no special lamps are needed.
This is extremely useful for other crops though.
Let's read that bit again
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.This means if we use a far red source on a plant we will get near instant phytochrome state change.
So what does this really mean?
Phytochrome decays from Pfr to Pr in the absence of 660nm wavelength light even with far red light source ~ 2 hours at which point the plant is "asleep" for want of a better word, this means*
1. using far red you can shorten your plant days by 2 hours or over a year save 30 days a year without effecting yield at all!
2. That's not all you can force plants in your garden into flower several weeks earlier than they would naturally go into flower using a timer instead of having to physically move them into dark by hand. Only very low wattage lamps will be needed.
*3. Also you should in theory be able to induce stretch with far red.
4. You can run 14/10 days for theoretically higher yields
