IMPORTANCE OF SPECTRUM: VERTICAL FARMING INDOOR CULTIVATION

Full Spectrum LED Blends Tailored for Vegetative and Flowering

Abstract:

The importance of cultivating indoor cannabis using full-spectrum LED lights that mimic the sun’s quantum response area of the visible light spectrum. Photosynthetic Photon Flux Density (PPFD), carbon dioxide (CO2) and temperature levels are the main variables that contribute to the rate of photosynthesis. Plants react to a range of photonic energy, between 400-700 nanometers (nm). When cultivating indoor cannabis, there are two main phases: propagation and flowering. Both phases require full spectrum, while propagation needs higher blue light and flowering needs higher levels of orange and red light. Green light helps drive photosynthesis, specifically in the lower leaves of plants. The Sea of Green method focuses on growing a larger quantity of smaller plants, while traditional growers cultivate a small number of large plants. Peak Roots provides highly engineered LED, full spectrum lights for the propagation and flowering phases of the grow cycle. For standard size cannabis plants, 1,500 µmol m-2 s-1 PPFD at 25-30 C has shown to contribute to an optimal rate of photosynthesis during the last few weeks of the flower cycle. For Sea of Green, indoor growing conditions of 1,100 µmol m-2 s-1 PPFD at 25-26 C exhibit the highest rate of photosynthesis during the last few weeks of the flower cycle. Keywords: Photosynthesis, Photosynthetically Active Radiation, Photosynthetic Photon Flux Density, Spectrum, PPFD, Cannabis Sativa L., Indoor Horticulture, Quantum Response, PAR

INTRODUCTION

Many factors play a role in plant growth and the process of photosynthesis. To create ideal indoor grow environments, it’s important to understand plant anatomy and what variables contribute to carrying out optimal plant functions. The goal for indoor horticulture is to manipulate an environment that increases the rate of photosynthesis. The main factors that play a role in photosynthesis are light, temperature and CO2 concentrations. Many benefits have been discovered when using light emitting diodes (LEDs) as a primary light source for indoor horticulture. Reduced thermal output and customized spectrums are key features of LEDs that have paved the way for the future of cultivating indoor cannabis. Plants undergo the biological process of photosynthesis, converting light energy to chemical energy. The interior layer of leaves contain mesophyll cells, which house chloroplasts (Reece et al., 2011). Chloroplasts contain the structures that carry out photosynthesis: the stroma, an aqueous fluid found throughout the inner membrane and thylakoids, sac-like structures that are stacked closely on top of one another. There are two main phases of photosynthesis, the Light-Dependent Reaction, which occurs in the thylakoid and the Calvin Cycle, which occurs in the stroma (Reece et al., 2011). Chloroplasts appear green due to the pigment chlorophyll. Pigments are substances that absorb different wavelengths of light and produce color, visible to the human eye. Visible light is only a fraction of the electromagnetic spectrum, ranging from gamma rays (<1 nanometer) to radio waves (>1 kilometer). The visible light spectrum falls between ultraviolet and infrared light at 380 to 750 nanometers (nm). On the violet end of the spectrum (380 nm), wavelengths are shorter and therefore, higher in energy. The deep reds in the spectrum (around 700 nm), are longer wavelengths and create an overall, lower energy. Light is measured by photons, non-tangible particles that have fixed quantities of energy based on their wavelengths (Reece et al., 2011). Natural sunlight creates the entire visible light spectrum. Within the spectrum lies the quantum response area, which drives photosynthesis (2018).

Light can either be reflected, transmitted or absorbed. Reflected wavelengths are not absorbed by pigments and will appear the color correlated to where they lie on the visible light spectrum. However, absorbed light will disappear. For example, if an object absorbs all wavelengths, it will appear black and if an object reflects all wavelengths, it will appear white. Light that is transmitted bounces from one object to another (Reece et al., 2011).


Figure 1: The Visible Light portion of the Electromagnetic spectrum, ranging from 30 – 50 nanometers.


Chloroplasts primarily absorb red and violet-blue wavelengths. They can also absorb green light, but mostly reflect it, giving them a green appearance (Reece et al., 2011). The three main pigments that are involved in photosynthetic processes are chlorophyll A, chlorophyll B and carotenoids. Chlorophyll A is the most utilized pigment in photosynthesis and it absorbs red, blue-violet light.

Chlorophyll B absorbs mainly blue light and is used to assist the function of chlorophyll A (2017). Carotenoids help enhance the absorbance of green light (2018). In addition, they act as antioxidants, blocking reactive oxygen species (ROS) (Reece et al., 2011). Free floating oxygen containing species can lead to cellular damage in plants and humans, alike. Plants automatically synthesize the amount of antioxidants they need in order to defend against free radicals. Carotenoids appear orange and red in color because they reflect wavelengths ranging from roughly 600-700 nm and absorb violet, blue and green (Reece et al., 2011).


Figure 2 Representative of the three main pigments involved in photosynthetic processes, correlating with relative amounts of light absorbed.


The first stage of photosynthesis is the light-dependent reaction that converts solar energy to chemical energy. his process occurs in the thylakoid, where water is split and light is absorbed by chlorophyll. he thylakoid membrane contains two main photosystems, reaction centers for harvesting light. Photosystems contribute to increasing surface area for absorbing more photons at a given time, versus the ability that one pigment has alone. Photosystems I and II are integral components of the light-dependent phase of photosynthesis. hey are named P00 and P60 due to the amount of light they absorb from the visible light spectrum, 00 and 60 nm, respectively Reece et al., 2011.


The second phase of photosynthesis is the Calvin Cycle, also referred to as the light-independent or the dark reaction. This reaction does not require photonic energy to take place. With this being said, it does not solely occur in the absence of light. The Calvin Cycle takes place in the stroma and is considered an anabolic process, where sugar, oxygen and water are built. The Calvin Cycle is broken down into three main steps: carbon fixation, reduction and regeneration of RuBP. At the end of the entire process of photosynthesis, glucose and O2 are produced (Reece et al., 2011).



Figure 3 Photosynthesis overview showing the anatomy of a chloroplast, reactants and products and the two phases of photosynthesis.


Visible Light Spectrum:


Only a portion of the visible light spectrum contains photonic energy that can be utilized by plants. Between 400-700 nm, lies the quantum response area, where photosynthetic activity is seen (Neiden, 2018). The ultraviolet and infrared sides of the spectrum have shown little to no effect on the rate of photosynthesis (Neiden, 2018). The quantum response area of the visible light spectrum is also known as Photosynthetically Active Radiation (PAR light). Generally, PAR light is measured as Photosynthetic Photon Flux Density (PPFD), an average number of photosynthetically active photons that fall on a given surface every second. PPFD is measured by micromoles/second (µmol m-2 s-1). PAR and PPFD are measured with a quantum meter, giving growers a precise measurement of light over a grid space. As stated before, natural sunlight drives photosynthesis, specifically by wavelengths that fall within the quantum response area. DLI needs to be taken into account when recreating the sun’s spectrum for indoor lighting. DLI stands for Daily Light Integral and measures the sum of PAR light given to plants over a 24 hour cycle (Currey, 2014). In an outdoor or greenhouse environment, DLI would vary depending what time of year it is. The benefit of growing indoors is having the ability to manipulate DLI without seasonal fluctuations. In addition to creating an optimal light schedule, maintaining an even distribution of light is critical for plants to grow at their full potential. When light is evenly spread across a grid space (measured by PPFD), plants can utilize equal amounts of light, leading to healthy plants and more consistent yields. Maintaining control over the amount of PAR light distributed in a canopy area reduces the risk for photo damage and can allow plants increase their rate of photosynthesis (Neiden, 2018).


Light Distribution:

Figure 5: Representing how the larger gaps between the LED light bars cause more uneven light distribution over a canopy. The image on the right demonstrates a more even distribution pattern by utilizing more surface area using wider LED panels.


Cannabis Lighting:


For cannabis, the grow cycle consists of two main phases: the propagation phase and the flowering phase. The propagation phase includes cloning and veg. Having the ability to customize spectrum, with LEDs during different phases of the grow cycle, has been revolutionary for indoor horticulturists. Typically, the propagation stage requires higher amounts of blue light. Plants have shown an increase in shoot tissue pigments and essential minerals, just by being exposed to higher levels of blue wavelengths from LEDs (Hardie, 2018). Plants have shown to become more nutrient rich with blue light during the propagation phase (Hardie, 2018). During the clone phase of propagation, Peak Roots recommends using 30-50 µmol m-2 s-1 PPFD to assist in root development.


Orange and red lights are needed in larger quantities during the flowering phase. Red light shows to be optimal for plant growth; however, when plants are grown in red light alone, they become thin and weak (Hardie, 2018). When plants are moved from full spectrum LED to a narrower spectrum, there is an overall decrease in biomass (Hardie, 2018). The combination of full spectrum LEDs with high levels of orange and red light is essential for flowering cannabis and maintaining healthy plants.


Traditional lighting systems that use high pressure sodium or metal halides have always had limitations when it came to customizing spectral light quality. Using LEDs for horticultural lighting provides the ability to create customized spectrums. In addition, LEDs have a much lower low thermal output and adjustable light intensities for specific species of plants (2018). With a lower thermal output, plants can be grown closer to the light source, maximizing space in the grow room. Growing plants closer to the light source uses less wattage, while maintaining equal or higher PPFD levels (Neiden, 2018). In LEDs, electricity is directly converted into photons which leads to “efficiency gains” compared to other light sources, where electricity is converted to heat and only a small amount of light. LEDs require less energy to emit the same amount of light compared to traditional lighting sources (Bergstrom, Delsing, L’Huillier, & Inganas, 2014)


In 2014, Isamu Akasaki, Hiroshi Amano and Shuji Nakamura won the Nobel Prize in physics for producing blue light LEDs, which has led to energy saving white light sources. Red and green diodes have been around for a long time, but these researchers found that without blue light, white lights could not be created (2014).

Figure 6: Quantum response portion of the sun’s full visible light spectrum demonstrated on the McCree Curve/Plant Sensitivity Curve. Quantum response is the area in which plants react to photonic energy from the sun.


The combination of red, green and blue wavelengths together create white light (Bergstrom, Delsing, L’Huillier, & Inganas, 2014). White lights contain the entire quantum response spectrum with an emphasis on blue light. Strong white lights have a higher level of orange and red light and still contain the full spectrum.


Cannabis sativa L. was first introduced in Western European medicine in the early 19th century to help treat conditions such as epilepsy, tetanus, migraines, fatigue, insomnia, rheumatism, asthma and trigerminal neuralgia. Over 70 cannabinoids have been isolated from the plant, showing medicinal properties such as appetite stimulating, analgesic, anti-inflammatory and anti-emetic effects. Anti-inflammatory phytochemicals block the cyclooxygenase enzyme (COX) in the biochemical pathway for synthesizing prostaglandins, the precursors that creates inflammation in the body. Over time, cannabinoids have been used for therapeutic effects specifically for cancer and AIDS patients (Chandra, Lata, Khan, & Eloshy, 2008).


The primary factors that play a role in the rate of photosynthesis, when growing cannabis, are light (PPFD micromoles/sec, µmol m-2 s-1), intracellular and ambient air concentrations of carbon dioxide (CO2 Ci/Ca micromoles, µmol) and temperature (Celsius). In addition, humidity is a variable that needs to be closely monitored. Photosynthetic efficiency is quantified by the moles of carbon fixed per mole of photons absorbed by the plant (Bugbee, 2016). Light directly contributes to plant growth, leaf thickness, chlorophyll production and overall net photosynthesis.


If light is absorbed in excess, it can cause stress to the plant, leading to photoinhibition and photodamage. Having the ability to control the number of photons projected onto a grid area will reduce the risk for plants to be deprived or overdosed with light (Chandra, Lata, Mehmedic, Khan, & Eloshly, 2015). Increasing blue light from 0-7% over a grow cycle has shown to double photosynthetic capacity. Specifically, red and blue light drive photosynthetic processes, primarily in the upper leaf layers, while green light penetrates deeper and has a stronger effect in the lower leaf mesophyll cells.


In combination with light, atmospheric and ambient air levels of CO2 drive photosynthesis, carbon absorption and plant growth. Doubling ambient air CO2 concentrations has shown to increase crop yields up to 30% (Chandra, Lata, Khan, & Eloshy, 2008).


Since CO2 is a necessary reactant in the process of photosynthesis, as light intensities and temperatures increase, CO2 concentrations will decrease. Carbon dioxide gets fixed through the light-dependent reaction and Calvin Cycle at a faster rate when plants are exposed to ideal growing environments. Since photosynthesis occurs within the mesophyll layer of the leaf, it is imperative to measure how accurately the entire process takes place. Mesophyll efficiency is the rate at which intracellular CO2 concentrations decrease, as it becomes fixed into oxygen (Chandra, Lata, Khan, & Eloshy, 2008).


Supporting Research:


In a study completed by Chandra, et al., researchers looked at the optimal indoor growing conditions for standard sized cannabis plants. The three main variables measured were PPFD (0-2,000 µmol m-2 s-1), temperature (20-40 C) and CO2 concentrations (250-750 µmol). Steady state photosynthesis is reached within 30-45 minutes, when plants are exposed to proper conditions. Cannabis sativa L. plants were left in the controlled environment for 45-60 minutes to ensure they were being measured within an accurate window of peak photosynthesis. Additional variables that were measured were the Rate of Photosynthesis (Pn) and Water Use Efficiency (WUE), a ratio of water used during plant metabolism to the amount of water lost during transpiration (E) (Chandra, Lata, Khan, & Eloshy, 2008). Transpiration is the process of water getting carried through the plant to pores underneath leaves, where moisture is converted to vapor and released into the atmosphere (2016).


Findings from this study exhibited that Pn and WUE increased up to 1,500 µmol m-2 s-1 PPFD and 20-25 C. Intracellular CO2 decreased with increasing PPFDs, since the plant utilized CO2 more rapidly as light increased. The highest intracellular CO2 was found at the lowest PPFD between 25-30 C. Overall, the highest mesophyll efficiency was found at 1,500 µmol m-2 s-1 PPFD and 30 C.


Another study completed by Chandra et al., looked at similar conditions for growing indoor cannabis (Chandra, Lata, Mehmedic, Khan, & Eloshy, 2015). Four different standard sized Cannabis sativa L. species were observed and they found similar results to study number one.




Each variety of cannabis was exposed to PPFDs ranging from 0-2,000 µmol m-2 s-1 at temperatures between 22-28 C and CO2 levels between 345-355 µmol. Plants were kept in conditions for 45-60 minutes to reach steady state photosynthesis and then observations were recorded. Rate of photosynthesis, water use efficiency (WUE) and mesophyll efficiency were also measured (Chandra, Lata, Mehmedic, Khan, & Eloshy, 2015).


There was an increasing trend in Pn with PPFD levels up to the highest level tested of 2,000 µmol m-2 s-1 . When the plants were exposed to 400-2000 µmol mm-2 s-1 PPFD, the rate of photosynthesis increased in the different species between 44-140%. As expected, while PPFD and transpiration increased, intracellular and ambient air concentrations of CO2 decreased. There was a total decrease of 41-58% in Ci/Ca ratio with PPFD levels up to 2,000 µmol m-2 s-1, which exhibits that light drives photosynthesis.


Increasing light intensity allows the plant to uptake more CO2, to be fixed into glucose and oxygen. Mesophyll efficiency also increased with increasing PPFDs in all four varieties of Cannabis sativa L. WUE increased up to 1,600 µmol m-2 s-1 plateauing and decreasing near 2,000 µmol m-2 s-1. Plants that have a higher Pn and WUE show potential to grow at a faster rate and have an increased biomass yield, compared to cannabis species with a low Pn and WUE in uncontrolled, fluctuating conditions. All four varieties presented a higher Pn and WUE in the upper range of PPFDs (Chandra, Lata, Mehmedic, Khan, & Eloshy, 2015).


Vertical Tiered Higher Density Plant Count Cultivation:


The Vertical Tiered growing method focuses on growing a large quantity of smaller sized plants versus few large plants. This style of growing aims to harvest plants quicker, since they don’t have to grow for the same duration, compared to traditional growing methods (2018). Traditional growing techniques require more height within the racks. Growing smaller, higher density plants takes up less space, making vertical tiered higher plant count growing far more efficient to maximize the grow area SF within the grow room.


The best way to ensure the vertical tiered higher density plant count style of growing is successful, is making sure plants are uniform in size when cloning and transitioning to flower. Transporting clones that are equivalent heights to vegetation and flower will maximize the likelihood for the most consistent yields (Wasteland, 2016). Peak Roots uses the vertical tiered higher plant count, paired with highly engineered lights that dose precision photons for each phase of the grow cycle.


Vertical Tiered Higher Density Plant Counts Correlation Between Lighting & Cabon Dioxide Levels:


Peak Roots has strategically designed an indoor growing method to reduce the overall length of the grow cycle. The cloning phase lasts for approximately two weeks, using the Veg spectrum light at 30-50 µmol m-2 s-1 PPFD. Next, the early veg phase lasts one week, where PPFDs are set to 265-280 µmol m-2 s-1 , as CO2 concentrations correlate exactly with PPFD levels. The flowering phase lasts eight weeks total, as PPFD and CO2 concentrations gradually increased from 350-1,100 µmol m-2 s-1 PPFD. As plants get larger and become more developed, there is a need for higher PPFDs and CO2 concentrations. PPFD and CO2 ramp up in unison through out the flower grow cycle.




Figure 10: Peak Roots vertical tiered higher density plant counts lighting and CO2 chart. This chart provides the precise micromoles and carbon dioxide levels for the veg and flower phase. For the cloning phase, Peak Roots recommends using 50-70 µmol m-2 s-1 PPFD and 30-50 ppm CO2 for approximately two weeks or fully rooted.





Quantum Response


Peak Roots’ LED lights are engineered to mimic the sun’s spectrum and the wavelengths within the quantum response area. Peak Roots has two main spectrums, the ICE) for propagation and the GOLD for flowering. The ICE spectrum is a white light that contains full spectrum with an increased level of blue light. The GOLD is a strong white light, which is also full spectrum, with an emphasis on orange and red wavelengths. These high tech lights put off little heat, are lightweight, one inch thick, contain thermal gaps, aluminum plated boards and come with a dial to customize light intensity throughout the grow cycle. Growing vertical tiered higher density plant count, paired with specialized lights can optimize the area within your grow space and increase overall cannabis yield in a shorter time frame, when compared to traditional grows. For the propagation phase, Peak Roots recommends keeping plants on an 18:6 schedule (lights on for 18 hours and off for 6). When plants are transported to flower, they thrive on a 12:12 schedule.


Figure 12: Representing the Peak Roots veg spectrum wavelength bands compared with the quantum response range.



Figure 14: Representing standard T5 fluorescent spectrum wavelength bands compared with the quantum response range.





Figure 13: Representing the Peak Roots flower spectrum wavelength bands compared with the quantum response range.



Figure 15: Representing High Pressure Sodium 1,000 watt spectrum wavelength bands compared with the quantum response range.



Spectrum Wavelength Bands


The best way to ensure the Sea of Green style of growing is successful, is making sure plants are uniform in size when cloning and transitioning to flower. Transporting clones that are equivalent heights to vegetation and flower will maximize the likelihood for the most consistent yields (Wasteland, 2016). Peak Roots uses the high density plant count grow method, paired with highly engineered lights that dose precision photon for each phase of the Sea of Green grow cycle. Peak Roots has concluded to maximize the quality and yields for flowering cannabis the Orange/Red Radiometric Flux% and Orange/Red PFFD% is best near 50% of the total wavelength band measurements.



Peak Roots ICE SPECTRA (Propagation & Vegetative Growth)


Figure 17: UL horticulture lighting report shows the Peak Roots Veg Spectra relative spectrum designed for propagation (vegetative and cloning) grow cycles.


Peak Roots GOLD SPECTRA (Flowering Growth)



Figure 18: UL horticulture lighting report shows the Peak Roots Flowering Gold Spectra relative full spectrum designed for flowering grow cycles as well is effective for all propagation.


Conclusion

In conclusion, photosynthesis is driven by light, CO2 concentrations and temperature. Cannabis sativa L. species have shown that the optimal rate of photosynthesis is found around 1,500 µmol m-2 s-1 in temperatures varying from 25-30 C when finishing tradtional larger size cannabis plants. Peak Roots has found that vertical tiered higher density plant count style of growing at a maximum of 1,100 µmol m-2 s-1 PPFD at 25-26 C is optimal when finishing high density of smaller flowering cannabis plants.

Understanding what conditions contribute to the maximum rate of photosynthesis can increase yield and biomass production. In addition to controlled environmental conditions, incorporating the full visible light spectrum within the quantum response range, throughout the grow phase is necessary to maximizing plant growth. Growing with LEDs, versus metal halide or high pressure sodium lights gives growers the ability to customize spectrum and light intensity DLI dosages for each stage of the plant’s grow cycle. In addition, using LEDs reduces total thermal output in a grow space. Peak Roots has designed a growing method which encompasses each of these factors. Maximize space, minimize electricity, grow with a high quality, full-spectrum LED light and give your plants exactly what they need to thrive.

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Chandra, S., Lata, H., Mehmedic, Z., Khan, I. A., & Eloshly, M. A. (2015). Light dependence of photosynthesis and water vapor exchange characteristics in different high THC yielding varieties of Cannabis sativa L. (Vol. 2). Journal of Applied Research on Medicinal and Aromatic Plants.

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Green Light Drives Leaf Photosynthesis More Efficiently than Red Light in Strong White Light: Revisiting the Enigmatic Question of Why Leaves are Green. Plant and Cell Physiology, 50(4), 684-697. doi:10.1093/pcp/pcp034

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Transpiration – The Water Cycle. (2016, December 2). Retrieved July 10, 2018, from https://water.usgs.gov/edu/watercycletranspiration.html  Wasteland, B. (2016, September 21).

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DAILY LIGHT INTEGRAL (DLI) CALCULATOR FOR INDOOR FARMING
Optimizing Light Exposure for Maximum Plant Growth