Far-Red Light: Inducing Growth With These Magical Photons
Far-Red Light: Inducing Growth With These Magical Photons
How adding separate channels of far-red and white LED will have a tremendous positive impact
Intro
Out of the many wonders of the universe, the sun and its light are one of the most fascinating ones. what was considered a source of life and light since ancient times is now also regarded as a generator of different types of energy in the form of various wave-lengths radiation. out of the vast spectrum, in between the visible and invisible light, lays the magic of far-red and its unique properties for plants.
Far-red light is a range of light at the extreme red end of the visible spectrum, just before infra-red light. Usually regarded as the region between 700nm and 740nm wavelength (Image 1), although it is barely visible to the human eye it has a powerful effect on plants. and even though sunlight has as much far-red as “regular” red, white LED does not. This makes the artificial light and supplemental light in disadvantage, unless corrective measures are put in place.
The raf-red is outside the range that traditionally is considered effective for photosynthesis 400-700 nm, because it is not effective by itself. But, as later studies showed, it is very effective when combined with white and/or blue red.
Among the benefits of far-red are cell expansion, stem elongation, increased rate photosynthesis, faster flowering and manipulation of plant shape. but its effect varies depending on different plant species, plant development stage and the ratio of red to far-red, often cited R:FR.
Photosynthesis
Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that can later be released to fuel the organisms’ activities. This chemical energy is stored in carbohydrate molecules, such as sugars, which are synthesized from carbon dioxide and water. It supplies most of the energy necessary for life on Earth.
The process is most productive when the absorption of quanta are equal in both the photosystem I (PSI) and photosystem II (PSII), assuring that input energy from the antenna complex is divided between the PSI and PSII system, which in turn powers the photochemistry, this is referred to as the “Emmerson effect”.
Emmerson effect
In 1939 Robert Emmerson discovered that the increase in the rate of photosynthesis after chloroplasts are exposed to light of wavelength 680 nm (deep red spectrum) and more than 680 nm (far-red spectrum). When simultaneously exposed to light of both wavelengths, the rate of photosynthesis is far higher than the sum of the red light and far-red light photosynthesis rates..
Shade Avoidance Vs Shade Tolerance
Leaves absorb most red light and blue light but reflect most far-red(?). Therefore, plants under a canopy or lower leaves of plants that are spaced closely together receive a greater proportion of far-red than red radiation – low R:FR ratio. Plants receiving this spectrum of light will usually behave in one of two ways.
Shade avoidance plants, which are flowering plants like tomato, cucumber, cannabis etc will typically elongate in an attempt to capture available light.
While shade tolerance plants, which are usually leafly plants like lettuce, spinach etc, their reaction to increased far-red light is leaf expansion, which can have significant increase in yields.
Phytochrome
Phytochrome proteins are red- and far-red-light-absorbing photoreceptors. They covalently bind to light-absorbing linear tetrapyrrole chromophore, photochromobilin, which is able to absorb light of wavelengths between 650nm (red) and 740nm (far-red).
Phytochromes control many aspects of plant development. They regulate the germination of seeds (photoblasty), the synthesis of chlorophyll, the elongation of seedlings, the size, shape, number and movement of leaves and the timing of flowering in adult plants.
Flower induction
Although increased far-red light can cause stem elongation in flowering plants it could also induce accelerated flowering as well as increased yields (which was observed in many crops).
When the natural days are short, low-intensity (photoperiodic) lighting is often delivered to promote flowering of long-day plants. For some long-day plants, flowering is accelerated most when photoperiodic lighting includes both red and far-red radiation.
Flower initiation and induction were promoted by night break treatment with a low R:FR light source, but was delayed by a high R:FR ratio. The promotion or delay of flower bud formation was accompanied by a decrease or an increase, respectively, in the number of nodes on the main stem at anthesis to the first floret.
*It is important to note that in some plants species and varieties far-red had little to none effect.
Conclusion
Although not all the mechnision are fully understood, there are many benefits of adding far-red light to LED grow lights both for leafy plants and different flowering plants in their seedling and vegtaive stage as well as in flowering.
The key factor for those effects is the ratio of R:FR, as well as the total flux of photons in these wavelengths.
Thus it is suggested that for full cycle of flowering plants a grow light with different channels for white, red and far-red will allow to maximize the benefits of far-red while minimizing it’s negative effect.
Reference
Zhen, S.; van Iersel, Marc W. (2017). “Far-red light is needed for efficient photochemistry and photosynthesis
Demotes-Mainard S(2016); Plant responses to red and far-red lights, applications in horticulture
Bryant DA, Frigaard NU (Nov 2006). “Prokaryotic photosynthesis and phototrophy illuminated”
Asuka Yamad (2006); Red:far-red light ratio and far-red light integral promote or retard growth and flowering in Eustoma grandiflorum (Raf.)
P. M. Pattison, J. Y. Tsao, G. C. Brainard & B. Bugbee (2018); LEDs for photons, physiology and food
Andrés, F., Coupland, G. (2016); The genetic basis of flowering responses to seasonal cues.