Why Your Plants Need A Daily Multi-Vitamin Called ROYGBIV
For nearly four decades indoor horticultural lighting hadn’t changed. Every cultivator, from the small clandestine home growers to medical commercial growers to big agricultural companies, kept using traditional high-intensity discharge (HID) bulbs in their gardens. Then things started to change. Soon we shifted from magnetic ballasts to newer, more efficient electronic and digital ballasts. Next came digital bulbs that were more compatible with the newer technology. As progress pushed forward, newer lighting options came forth. LED lamps, ceramic bulbs, double-ended bulbs, induction lamps and plasma lights are some of the many options now available in the market place for cannabis growers. But which lighting technologies are truly best for horticultural applications? As always, we fall back to science for the answer…
Photobiology 101
Plants exist on Earth only because of a very unique process known as photosynthesis. Photosynthesis is a miraculous biological process whereby the Sun’s energy is captured and stored by a plant in a series of events that convert the pure energy of light into the biochemical energy needed to power life. In short, the Sun’s energy, which travels to plants in the form of visible radiation we call light,
takes the form of elementary particles knows as photons. These subatomic particles constitute electromagnetic radiation, a radiant energy that plants can absorb through various pigmentations in their leaves. It is this energy that allows for a photochemical reaction to take place. In it’s most simplistic form, the equation for photosynthesis looks like this:
CO2 + H2O + Photon Energy = Organic Matter (glucose) + O2
The glucose created are the sugars, or plant food, created by the photosynthetic process. Without sunlight, plants – and all life – on Earth would have never come to be. So what does all this mean for our indoor cannabis gardens? Simply stated, this means that our artificial indoor horticultural lighting should, to the best of our ability, mimic nature’s own natural light source which plants (including cannabis) have evolved under for many millennia. This means that artificial light created by grow lamps should also carry the same photosynthetically active radiation (PAR) that sunlight does. Going all the way back to the 1970’s, our HID bulbs did as well as technology would allow in this regard.
However, in the past five years major strides have been made in lighting technologies, and now many new products boast varying spectrums for optimal plant growth and yield. Some even claim new lighting developments are even better for our plants than full spectrum sunlight. How do we know which claims are valid, which shortcuts (if any) are viable, and how these varying spectrums will affect our gardens before dropping buckets of money on new lighting gear? To answer these questions, let’s first take a look at a breakdown of the various spectral colors (also known as wavelengths or frequencies) to see just how exactly they contribute to photosynthetic processes, plant development, yield size and quality.
How Various Spectral Wavelengths Affect Photosynthesis
We all remember our good friend ROY.G.BIV from grade school science class – an acronym for the colors: Red, orange, yellow, green, blue, indigo, violet. These colors, or wavelengths, are measured in nanometers (nm) and comprise the visible spectrum of light.
Much research has been done on the effects of various light wavelengths on plant growth. We know that different photosynthetic pigments within plants utilize different wavelengths and we know that plants use those various wavelengths to accomplish different growth and development processes. In cannabis, these processes directly affect yield as well as cannabinoid and terpene production. Let’s learn more about the benefits of different spectral wavelengths.
Ultraviolet Light (10nm-400nm)
Overexposure to UV light is as dangerous to most flora as it is to humans. Still, small amounts of near-UV light can have beneficial effects for cannabis. In many cases, UV light is an important contributor to plant colors (pigments, such as purple or bright green), tastes and aromas (terpenes). This is an indication of near-UV light effect on metabolic processes. Research shows that 385nm UV light promotes the accumulation of aromatic organic compounds, enhances antioxidant activity of plant extracts, but does not have any significant effect on growth processes.
In cannabis specifically, the plant uses its trichomes (resin glands) to act as a sunscreen to protect against abnormal amounts of UV. Some growers have tried to use larger amounts of UV to produce more resin and thus increase potency. Small increases in potency have been recorded using UV lights, but most advanced growers do not advocate for “stress factors” like this to increase resin production.
Blue Light (400nm – 520nm)
The blue light spectrum, which for our purposes includes indigo and violet, enables photoreceptors such as cryptochromes and phototropins to mediate plant responses such as phototropic curvature, inhibition of elongation growth, chloroplast movement, stomatal opening and seedling growth regulation. It affects chlorophyll formation, photosynthetic processes, and through the
cryptochrome and phytochrome system, raises the photomorphogenetic (form and structure) response.
Blue wavelengths at around 450nm encourage vegetative growth through strong root growth and intense photosynthesis and are often used as supplemental light for seedlings and young plants during the vegetative stage of their growth cycle, especially when “stretching” must be reduced or eliminated. Blue wavelengths also carry the highest amount of photon energy out of all the spectral
wavelengths.
Green light (520nm – 560nm)
Contrary to popular believe, not all green light is reflected by plants’ chlorophyll. In fact, green light is often used as a tool for eliciting specific plant responses such as stomatal control, phototropism, photomorphogenic growth and environmental signaling. When combined with blue, red and far-red wavelengths, green light completes a comprehensive spectral treatment for plant physiological activity. Because green light can penetrate further into the leaf than red or blue light, in strong white light (i.e., full spectrum light) any additional green light absorbed by the lower chloroplasts would increase leaf photosynthesis to a greater extent than would additional red or blue light. Thus the presence of green light will serves to boost plant energy and yield, especially in bigger plants during the flowering cycle.
Yellow/ Orange Light (560nm – 640nm)
The 624nm region has the highest photosynthetic relative quantum yield for a range of plants. At the same time, it’s action on red-absorbing phytochrome is considerably weaker compared to that of 660 nm red light and can be used to balance the phytochrome equilibrium towards lower values (closer to those of daylight) than those achievable with 660 nm red light, especially when used
together with 730 nm red light.
Red Light (640nm – 700nm)
Red light, the longest wavelength in PAR, affects phytochrome reversibility and is the most important for photosynthesis, flowering and fruiting regulation. These wavelengths encourage stem growth, as well as chlorophyll, flowering, and bud production. Several studies have demonstrated that plants showed the most growth in the vegetative phase under 650 nm light. Similarly, in the germination phase, irradiation of 680nm spurs the greatest growth rate for freshly popped seeds.
The 660nm wavelength has a very strong photosynthetic action and also exhibits the highest action on red-absorbing phytochrome in regulating germination, flowering and other processes. Also, red light is very effective for light cycle extension to prevent flowering of short-day plants such as cannabis.
Far Red (700+nm)
Even though the 730nm wavelength is outside the PAR range, it has the strongest action on the far-red absorbing form of phytochrome, converting it back to the red-absorbing form. Studies show it is necessary for plants requiring relatively low values of the phytochrome photoequilibrium to flower, thus far red can be used at the end of each light cycle to promote flowering in short-day plants.
Artificial Sunshine
One of the more intriguing advancements in lighting technologies of the past few years is the unit shown here, originally produced by Life Light Technologies and now manufactured by Garrison Technologies, Inc. The light spinners come in three-, four- and six-arm units, spinning at the same RPMs as a ceiling fan (which is to say, quite fast).
The real science, however, comes into play with the SunPulse bulbs, which came in (seven) different Kelvin rated temperatures. Each bulb produces a specific wavelength (color) of light, which is traditionally measured by its heat signature. By adding a different bulb in each arm, the spinning lamp creates a full spectrum, white light that comes the closest to that of natural sunlight out of all new lighting tech and has been unmatched since.
Furthermore, the spinning action was calculated such that the light was delivered to plants at the same beat frequency as the sun’s natural light, meaning the plants received it all at once as white light, same as they would outdoors in nature. Additionally, the bulbs are true, digitally compatible bulbs with pulse start technology (made specifically for the new digital/ electronic ballasts) making them far more efficient than our traditional HID bulbs.
Pigments & Light Absorption
One method for determining spectral absorption curves (as seen in Figure 1) for plant photosynthesis is to closely examine the pigments that are in the leaves and directly involved in photosynthesis. Scientists can measure the rate at which these pigments absorb light and can even break down their absorption rates of each wavelength.
Leaf pigments such as chlorophyll generally reside within chloroplasts, which are subunits of plant cells. Chloroplasts’ main role is to conduct photosynthesis, where chlorophyll captures photon energy from sunlight and converts it and stores it in ATP and NADPH (energy-storage molecules). They then use the ATP and NADPH to make organic molecules from carbon dioxide in a process known as the Calvin cycle. These organic molecules are the basis for plant food. The pigments in chloroplasts each absorb different light wavelengths and they absorb them at varying rates. As the photosynthetic process moves throughout the leaf, various wavelengths of light are absorbed at different locations, providing varying forms of light energy, much like a multi-vitamin provides varying minerals for humans to create proteins and energy. Here’s a look at the major pigment players in plant leaves and the specific wavelengths they utilize most.
- Chlorophyll-a: This is the most abundant pigment in plants. Chlorophyll-a absorbs light with wavelengths of 430nm (blue) and 662nm (red). It reflects green light, making plants appear green to humans. Chlorophyll-a contains certain constituents that enable the pigment to absorb photons from light.
- Chlorophyll-b: This molecule has a structure similar to that of chlorophyll-a. It absorbs lighter shades of red and blue light of 453nm and 642 nm maximally. It is not as abundant as chlorophyll-a, and probably evolved later. Chlorophyll-b increases the range of light a plant can use for energy and can absorb some yellow and heavier oranges as well.
- Carotenoids: This is a class of accessory pigments that occur in all photosynthetic organisms. They are completely hydrophobic (fat soluble) and exist in lipid membranes. Carotenoids absorb light maximally between 460 nm and 550 nm and appear orange or yellow to us to humans as most of these wavelengths is reflected. Carotenoids can absorb the green wavelengths reflected by both chlorophyll-a and –b.
Simple Conclusions
At the onset of this article we asked which lighting technologies are truly best for horticultural applications? As we summarized the science we have accumulated over the past several decades, we saw that every color of the visible light spectrum has a significant role to play in a plant’s development. These developments not only affect growth rate, plant structure and health, but also yield and – in terms of cannabis – potency, as both cannabinoid and terpene production are dependent on optimal plant development.
Next we begin to understand photosynthetic processes more clearly as we delve deeper into the plant and study the pigments that absorb light’s various wavelengths. We see here that at every point along the way various pigments are absorbing various wavelengths at different rates and in different places within the plant. Each pigment and each color wavelength has a specific purpose and
contribution to the overall process of creating sugars. In many regards, light acts as a multi-vitamin for plant food, with each wavelength acting as a mineral that contributes a specific energy and function towards creating plant food. These are the processes that lead to better plant growth and health, which in turn increases yield and potency in cannabis.
When we combine all these facts with the simple notions of Mother Nature and evolution, it becomes quite clear that full spectrum, white light provides the best growth environment for plants. However, we also see via our spectral absorption curves a few surprises. First, green light is not reflected nearly as much as most people assume. Further, yellow and orange wavelengths appear to be
absorbed minimally and offer the lowest absorption rates of any of the visible wavelengths. This brings into question just how effective (and efficient) the more orange-hued HPS bulbs really are during flowering and offers a strong argument towards supplemental lighting during the flowering stage in order to achieve a fuller spectrum of white light.
In the end, we can always fall to science for the answers, but there is also the easy – and more obvious – solution… the outdoor classroom. All we need to do is study plants in their natural environs and take a look around. When we step outside and see what makes a 12-foot cannabis tree thrive, all we need to do it look up.
