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What Types of Light Produce the Best Cannabis? New Study Says It’s These 2 Wavelengths

All plants need light in order to perform photosynthesis, but the type of light has a significant effect on how plants grow and function. Sunlight is considered full-spectrum light, including all wavelengths that are useful to plant and animal life, from infrared to ultraviolet. However, some wavelengths are more essential to plant life than others, and because cannabis plants are engineered and bred for specific effects and applications, there’s great potential to control the light spectra cannabis plants are exposed to in order to produce flower with different psychoactive and therapeutic properties. 

Lead researcher Dr. Nirit Bernstein and her student Nadav Danzigerab, based out of the Volcani Center in Israel, recently conducted a study to determine how variations in light spectra affected the flower yield, as well as the presence of different compounds, in cannabis plants. While previous research has suggested that full-spectrum light is the most beneficial to plant growth, the results of this new research suggest otherwise, finding that red and blue light are the best for cannabis plants.

There could be many reasons for this, Bernstein says, “for example, specific wavelengths other than red and blue may have stimulated developmental shifts in [other] plants that favored vegetative or reproductive development.” Or, certain wavelengths could have stimulated energy-demanding processes, thereby shifting the energy balance away from producing flowers or cannabinoids in order to devote energy to something else, such as downstream metabolic processes. 

There’s a lot we don’t know, but Bernstein’s research offers surprising insight into the possibility of “alter[ing] the cannabinoid profile in cannabis by manipulating the light spectrum… a promising avenue for customizing the bioactive profile for the benefit of both patients and growers,” as she writes in the paper.

How Light Wavelength Affects Yield and Composition

Bernstein and Danzigerab tested a number of different spectra, produced either from LED or high-pressure sodium lights, in medical cannabis plants. They found that a one-to-one blue-red light ratio produced the highest inflorescence yield (or the entire amount of flower produced by the cannabis plant). In fact, compared to the plants exposed to red and blue light, plants exposed to full-spectrum light did not evidence any increased yield.

Why did red and blue light produce the highest yield? The reasons for this stem from the photosynthetic processes of all plants as well as the specific properties of cannabis. Total plant biomass and yield are generally increased by efficient photosynthesis, and photosynthesis is driven by a plant’s ability to capture light in order to fix carbon (i.e., convert carbon from CO2 into organic compounds that can be used by the plant). Chlorophyll a and b are the pigments responsible for capturing light, and they most effectively absorb red and blue wavelengths.

cannabis lights
According to a recent study, when compared to plants grown in full-spectrum light, plants grown in blue and red wavelengths of light had greater cannabis yields.

Furthermore, more so than many other plants, cannabis produces a large amount of “secondary metabolites” as a by-product of photosynthetic metabolism. Bernstein explains that secondary metabolites sometimes comprise up to 20 percent of the cannabis plant’s dry weight, and this level of production requires massive amounts of energy. That means that cannabis needs intense light at optimal wavelengths to maximize the efficiency of photosynthesis. Red and blue light are those optimal wavelengths. 

What are “Secondary Metabolites” in Cannabis?

Secondary metabolites are small organic molecules that are produced by the cannabis plant (and many other plants), but aren’t necessary for growth, development, and reproduction. Cannabinoids fall into the category of secondary metabolites, which includes the precursors of THC and CBD, the most widely-known cannabinoids. 

Cannabis flower contains many other secondary metabolites, including terpenoids, sterols, and flavonoids—over 1,000 secondary metabolites have been identified in cannabis flower. Bernstein and Danzigerab analyzed 19 cannabinoids and reported on the concentrations of nine of them (CBCA+CBC, THCA+THC, CBDA+CBD, GBGA, CBDVA, and THCVA). Bernstein says, “all other analyzed cannabinoids were not detected, meaning they were not there or their concentrations were very low, below the detection limit.” 

Indeed, the cannabinoid profile can vary tremendously between cultivars and in response to environmental conditions. The diverse profile of compounds in cannabis produces what is referred to as the “entourage effect,” where THC’s potential is believed to be increased through the combined effect of different metabolites, synergistically producing psychoactive effects different from what THC produces on its own. 

The authors write that “variation in quantities and ratios between these metabolites may affect the therapeutic potential and patients’ response.” We are just beginning to understand how these metabolites interact in the human body. Still, the fact that we may soon be able to control the ratios of metabolites with much more precision opens the door to more methodologically sound research and precision medicine.

Plant Size Also Affects Variation in Cannabinoids

The authors of this study have conducted additional research on how the architecture of cannabis plants affect the uniformity of these secondary metabolites throughout the plant and flower. 

Plant organs are highly sensitive, able to sense small changes in their environment. Plant architecture, the way the plant grows and is organized in space, can produce variation in the micro-climates within the plant, especially as plants get larger. For example, in a large plant, some leaves may be more shaded by leaves higher up the stem, reducing the amount of light available to lower leaves, and, in turn, reducing photosynthetic efficiency. This creates variation in cannabinoid profiles even within a single plant.

However, the authors also found that “manipulations of plant architecture” (e.g., removing bottom branches and leaves that receive less light) increases the local concentration of cannabinoids in regions that were getting less light, and increases the uniformity in cannabinoid concentrations in the plant as a whole. Although growers may want to make minute adjustments in cannabinoid concentrations, it’s advantageous if these concentrations are homogenous within the plant, as it yields a more uniform product and allows consumers and prescribers to know what to expect.

Light spectra and plant architecture influence how the cannabis plant is able to utilize available light, and with this more precise data, growers can make informed decisions about how to fine-tune the presence and concentrations of cannabinoids. In an era where cannabis production and marketing is increasingly specialized and targeted for particular uses and consumers, our understanding of the science lags behind. This research aims to change that. 

Still, “the processes are complex,” Bernstein says, “and in order to get an overall understanding of light spectrum effects on cannabis yield quantity and quality, much research is still required.” Bernstein and her team plan to focus next on the effects of specific light spectra on the metabolome, which she explains as “the secondary metabolite profile that develops in the plant.” 

She also plans to study the responses of various developmental stages of the cannabis plant to light spectra, in order to optimize cultivation practices. Bernstein lays out an example: the effects of light during the first two weeks under short photoperiod (when the plant is not receiving many hours of light, but grows rapidly in height) may be very different than those at a later stage of flowering when the cannabinoid profile reaches chemical maturation. Growers and consumers alike will await further research.

Other Stories by Kate Raphael:

Environmentally Unfriendly: Indoor Cannabis Production Is Hotboxing Our Atmosphere

Paying The High Price: Why The Cost Of Cannabis Is A Public Health Question

Cannabis Consumers in Canada & the U.S. Respond to Warning Labels in New Study