Growers have a lot of choices to consider when selecting lighting systems to produce plants, including efficiency and productivity. Cultivation approach (indoor or greenhouse), technique (single-tier or vertical racking), and cultivar are important factors and can influence which equipment can do the job effectively.

Horticultural lighting is a fast-growing segment of the electric load for many U.S. utility companies, and lighting for indoor cannabis cultivation accounts for much of this growth. The “2018 Cannabis Energy Report,” published by New Frontier Data and co-authored by Resource Innovation Institute (RII) and Scale Microgrid Solutions, estimated that legal cannabis cultivation in the U.S. consumes approximately 1.1 million megawatt hours of electricity annually—enough to power 92,500 homes—and recommended that the industry “evaluate energy-efficient and renewable energy technologies” to rein in its carbon footprint.

The U.S. Department of Energy recommends that growers transition their lighting to light-emitting diode (LED) technology, a move the agency says could reduce electricity usage by at least 40% and save operators approximately $240 million. The industry is poised for the transition; a 2019 Strategies Unlimited report forecasted that the LED market for cannabis will grow more than 300% in the next five years.

Evaluating LED Solutions

Growers who are interested in researching LED technology and looking for unbiased information may want to start with the DesignLights Consortium (DLC), a nonprofit organization with a board of directors that includes leadership from energy and utility companies. The DLC instituted a first-of-its-kind performance standard for horticultural lighting in 2018. The result of two years of stakeholder engagement, the DLC’s Technical Requirements for Horticultural Lighting set standards for efficacy, safety, durability and other criteria that manufacturers must meet to get their LED products included on the DLC’s Horticultural Lighting Qualified Products List (QPL). Currently, listed products are at least 10% more energy efficient than the most efficient legacy grow lights (i.e., double-ended high-pressure sodium (HPS)). The DLC third-party verification process for horticultural lighting does not exist for non-LED lighting solutions like High Intensity Discharge technology (e.g., HPS, metal halide).

The QPL is a searchable, filterable online resource that gives grow light shoppers a map through what can be a confusing landscape of options. With 226 products listed and more reviewed and added regularly, the QPL offers cannabis growers transparent performance data that allows apples-to-apples comparisons of LED fixtures and the ability to verify manufacturers’ marketing claims.

An increasing number of efficiency programs rely on the DLC’s Horticultural QPL for designing energy efficiency (EE) programs for commercial cultivators. Nearly 60 EE programs serving growers in 31 states and four EE programs in Canada require use of QPL-listed products as a prerequisite for EE incentives, and many others have incorporated the DLC Technical Requirements into their programs while not yet requiring listed products. Massachusetts and Illinois, which have cannabis-specific EE regulations, offer use of the DLC Horticultural Lighting QPL as one route for compliance. (The QPL website includes a filter to facilitate cultivators’ search for regulatory-compliant products in these states.)

In addition to efficiency, manufacturers’ longevity and safety claims must be verified for LED fixtures to get listed on the Hort Lighting QPL. Notably:

• Products must be tested at the worst-case electrical scenario. This conservative assessment means that growers who use a listed product at a different voltage may experience better performance than the fixture’s listed performance.
• LEDs must produce a maintained photon output of at least 90% of initial output for at least 36,000 hours—ensuring longer life and lower maintenance costs compared with HPS fixtures.
• Drivers and fans must have a lifetime of at least 50,000 hours, increasing reliability.
• Fixtures must have a warranty of five years.
• Fixtures must be certified by an Occupational Safety and Health Administration (OSHA) Nationally Recognized Testing Laboratory, or Standards Council of Canada (SCC)-recognized body, to meet specific safety benchmarks deemed applicable to horticultural lighting products by that safety organization.

Eighteen months after rolling out its horticultural lighting Technical Requirements, the DLC announced the policy’s first major update in September 2020, scheduled to take effect March 31. This update maintains the current efficacy threshold but adds new optional reporting requirements that extend the performance information to include additional UV and far-red wavelengths, so that in the future the QPL can offer products with more diverse ranges of light recipes. The update also includes use of the ANSI/CAN/UL8800:2019 Safety Standard for Horticultural Lighting Equipment And Systems, which has specific rating requirements for environmental factors such as damp locations, ingress protection codes, photobiological safety ratings, and UV material protection.

The DLC is considering further updates this summer under Version 2.1 that would add three new categories of fixtures to the Horticultural Lighting QPL: DC-powered fixtures, liquid-cooled fixtures, and LED replacement lamps. Look for updates on the DLC’s Horticultural Lighting Program website.

Bright Questions for Manufacturers

Before growers consider replacing their light fixtures, they should consider creating a baseline of their operation in RII’s benchmarking tool, Cannabis PowerScore, to record their current Key Performance Indicators (KPIs) for energy efficiency, productivity and lighting performance so they know how their operation is performing with their current lighting technology. As they upgrade their lighting systems and potentially transition to LED solutions, they should continue to benchmark their facility periodically to quantify the benefits with PowerScore, verifying the improvements in their KPIs to measure their success.

RII’s analysis of aggregate PowerScore data shows that indoor cannabis cultivation operations growing with LED for flowering achieve 34% better average electric facility efficiencies and 80% better average electric production efficiencies than indoor facilities using double-ended (DE) HPS lighting for the flowering growth stage.

Growers who are ready to evaluate lighting solutions and the manufacturers serving their market should ask suppliers:

1. What is the warranty of your product?
2. What is the rated fixture life and control equipment life? What tests were performed to validate the claim?
3. Has your product been tested on my cultivar(s)?
4. What is the spectral quantum distribution (SQD) of your product, and does it align with my desired light recipe?
5. Can you provide Photosynthetic Photon Intensity Distributions (PPID) to show the photosynthetic light emitted at different angles so I can plan lighting layouts? (The PPID allows you to create your own lighting plans rather than relying on the manufacturer.)
6. What technical assistance is available during the design phase for lighting plans?
7. What help can you provide if I encounter problems during production?
8. Is there a cost for technical support or limitations on when/how to access it?

When growers ask suppliers about LED lighting solutions, they should verify whether the products are DLC-listed. Growers can note that SQD and PPID images are provided for LED products on DLC’s Horticultural Lighting QPL. If a product is DLC-listed, cultivators can ask the manufacturer about their experience getting help from utilities with rebates to buy down the first cost. In 2018, the average cost of flowering LED fixtures was around $1,500 compared to conventional HID lighting solutions like HPS, which cost around $500 on average in 2018 and have continued to decrease in price faster than LED products, according to market research completed by RII member Energy and Resource Solutions. First cost of LED products can be a barrier to adopting this emerging technology.

Measuring LEDs Effect on Plant Expression

A challenge of using LED horticultural lighting can be understanding how it stimulates plant responses like photosynthetic action and secondary metabolite production. Predictive metrics like PPF or photosynthetic photon efficacy (PPE) are, as the names indicate, based on light-stimulating photosynthesis.

The metrics used by RII, DLC, fixture manufacturers and others are standardized by the American Society of Agricultural and Biological Engineers (ASABE). These metrics do not predict light’s ability to produce other responses, like the production of specific secondary metabolites such as CBD, THC and terpenes.

In the U.S., research organizations are studying hemp production, sometimes with collaboration with lighting manufacturers, and publishing results for different spectral combinations and light amounts. At this time, no metrics considering the interactive effects of spectrum and dose on specific secondary metabolites have been proposed.

RII and DLC hope that additional metrics will begin to be considered and developed, so that cultivators can better predict which lighting system is going to help them optimize the biological results. In the meantime, the industry continues to use photosynthetic metrics and empirical data to inform additional desired outcomes.

Improved facility efficiency and productivity are possible with LED horticultural lighting solutions, as they save energy, while more non-energy benefits are yet to be researched and quantified. Tested and certified LED products on the DLC QPL can be relied upon for cultivation, so growers should consider the variety of trustworthy options on the DLC QPL when they make their next lighting purchase.

Anticipating and Overcoming the LED Learning Curve

Another challenge of using LED horticultural lighting can be navigating the learning curve of LED technology and modifying Standard Operating Procedures (SOPs) when necessary. There are a few considerations during design and construction that can optimize grow environments to be adaptable and successful as growers use their new equipment, and peer-reviewed guidance is available to help them maintain productivity as they grow with LEDs for the first time. RII’s LED lighting best practices guide offers tips for successful installation and operation of LED products. RII’s Massachusetts best practices guide offers tailored recommendations for a market that is adopting LED lighting technology to comply with environmental regulations. Download both guides here.

Authors’ Note: This article is the final in a five-part series of guest columns by Resource Innovation Institute (RII). Key terms introduced above are italicized and described in more detail in the guides at ResourceInnovation.org/Resources.

Gretchen Schimelpfenig, PE, is the Resource Innovation Institute’s (RII) Technical Director and manages the organization’s Technical Advisory Council. She is a licensed Civil Professional Engineer in California and Vermont.

Leora Radetsky, MS, LC is Senior Lighting Scientist at DesignLights Consortium (DLC), where she develops lighting solutions that promote energy optimization, quality and more in horticultural and architectural settings.

A recurring series focusing on plant cultivation by university researchers

One of the primary goals for cannabis cultivators is to optimize plant growth for stronger, healthier yields. To optimize plant growth, monitoring and managing nutrient levels is essential; however, numerous factors can affect nutrient availability and uptake for cannabis plants. As growers know, cultivation is a balancing act of providing adequate nutrient levels in proper ratios, and, most importantly, ensuring that the substrate pH is within the recommended range. Each of these factors properly applied together optimize plant growth, but if one factor is out of balance, the plant will suffer.

Nutrient “lockup” or “lockout” is when a particular nutrient is unavailable for the plant to uptake. This is usually caused by an elevated substrate pH, a situation that has plagued cannabis growers for many years. A second problem is improperly balanced nutrient levels. This is referred to as an antagonism. In addition, one must ensure that adequate levels of fertility are provided. While these can all limit nutrient availability, their fundamental causes are different. And perhaps the most important factor is substrate pH.

Tip #1: Find The pH Sweet Spot and Avoid Nutrient Lockout

Substrate pH is important to plant nutrition, as it directly impacts plant nutrient availability (Fig. 1, above). Some nutrients become more available, while others become unavailable depending on the substrate pH level. Nutrient lockout can be avoided by maintaining the recommended substrate pH for cannabis, between 5.8 to 6.2. This target range is based on research trials conducted at North Carolina State University. Levels below and above that range should be viewed as marginal zones in which corrective measures should be taken to avoid nutritional problems. Levels below pH 5.5 or higher than 6.5 can lead to an array of nutritional issues, which includes nutrient lockout.

Low pH

When substrate pH levels fall below 5.5, micronutrient availability increases. Substrate micronutrients (boron (B), copper (Cu), iron (Fe), manganese (Mn) and zinc (Zn)) become more readily available when the substrate pH becomes too acidic (see the wider bands in Fig. 1), with the exception of molybdenum (Mo). The most prominent problems observed in greenhouse production occur with Fe and Mn toxicity.

A low substrate pH can also hinder both Ca and Mg availability, but usually fertilization programs provide adequate levels of those elements, preventing deficiencies even if the substrate pH is low.

Symptoms of Fe and/or Mn toxicity may appear as bronzing on older leaves. However, in experiments conducted at North Carolina State University, we did not observe symptomology of lower leaf blackening or bronzing with cannabis plants, only stunted growth (Fig. 2, above). These results suggest that given normal levels of micronutrients in the fertilizer solution, cannabis can adequately regulate micronutrient uptake under low substrate pH conditions and avoid leaf symptomology. However, in a follow-up research study, we found if excessive micronutrients were supplied, lower leaf bronzing does occur. Therefore, it is important to provide adequate, but not excessive, micronutrient levels to cannabis to help prevent toxicity symptomology development in case the substrate pH dips too low.

High pH

When the substrate pH is elevated, cannabis can develop interveinal chlorosis (yellowing) on the youngest leaves (Fig. 3, above). This is a common situation that occurs with many greenhouse-grown species, such as petunias, when the increased substrate pH makes micronutrients such as Fe unavailable to the plant. This symptomology or lockout can occur even if adequate Fe levels are being provided in the fertilizer. While deficiencies of other micronutrients such as B, Cu, Mn and Zn also can occur, problems of Fe lockout are most commonly observed.

The good news is that micronutrient toxicities and lockout can be avoided by monitoring and managing the substrate pH. (Read “How to Establish a Cannabis Nutrient Monitoring Program” for more guidelines.)

Tip #2: Ensure the Proper Ratios to Prevent Tie-Up

Providing plants the proper nutrient balance also will help avoid induced deficiencies. Excessive levels of one element will cause an antagonism against the others, or a tie-up of nutrients (Table 1, above). In severe cases, plants will develop nutritional deficiencies. In this case, too much of a good thing is bad.

For instance, excessive potassium (K) will most commonly result in either calcium (Ca) deficiency or magnesium (Mg) deficiency symptoms. Many instances of Mg deficiency in cannabis may be due to excessive K or Ca being supplied and not because of the lack of available Mg to the plant. Abnormally high levels of one element normally does not result in toxicity symptoms. For cannabis, K, Ca, and Mg all appear to be needed in larger quantities compared to other greenhouse floriculture species. In general, the rule is to provide K, Ca and Mg in a 4:2:1 ratio to avoid antagonisms. For commercial cannabis production, we recommend a similar ratio of about 200 ppm K to 100 ppm Ca to 50 ppm Mg.

Managing microelements also can be challenging. The margin of error between deficient and excessive concentration rates is very narrow. Until you become comfortable mixing your own micronutrient fertilizer salts, it’s safer to rely on premixed micronutrients or the micros provided in commercial fertilizer blends. This will help avoid micronutrient tie-ups.

Providing the essential elements at the right balance is the key to optimizing plant growth.

Tip #3: Optimize Nutrient Levels to Prevent Nutrient Disorders

The final step in preventing and diagnosing nutrient lockup is ensuring that your fertilization program is providing adequate nutrient levels to the plants. Optimizing fertility management is a strategy of supplying the appropriate level of both the micronutrients and macronutrients to cannabis to meet the demands for plant growth. If the supply is too low, then plant growth is hindered because of nutrient deficiency (Figs. 4 & 5), and the plant will produce fewer and/or smaller flower buds.

Elevated fertilizer levels can lead to excessive leaf and shoot development at the expense of flower growth. Excessively high levels of fertilizer in the substrate also can lead to stunted growth, leaf necrosis and nutrient imbalances (Fig. 6). The good news is that conducting in-house nutrient monitoring by measuring the electrical conductivity (EC) levels will enable you to avoid this situation and ensure your cannabis crop is on track. (For additional details, read Cannabis Business Times articles “Optimizing Electrical Conductivity" and “Troubleshoot Nutrient Problems Before They Occur.”)

Conclusion

Providing adequate fertility, balancing the nutrient ratios, and managing the substrate pH will go a long way in avoiding deficiencies, nutrient tie-up and nutrient lockout, leading to better growth and ideal yields.

Dr. Brian E. Whipker is a professor of floriculture at North Carolina State University specializing in plant nutrition, plant growth regulators and diagnostics. During the past two years, he co-authored eight scientific journal articles on the impact of fertilization with greenhouse species and three disorder diagnostic guides. Dr. Whipker has more than 28 years of greenhouse experience working with growers.

Paul Cockson is a graduate research and teaching assistant at North Carolina State University. He has a degree in plant and soil sciences with a concentration in agroecology. For the past few years, he has worked in the plant nutrition lab at NCSU with Dr. Brian Whipker.

Patrick Veazie is an undergraduate researcher at North Carolina State University.

David Logan is an undergraduate research assistant at North Carolina State University.

Dylan Kydd is an undergraduate research assistant at North Carolina State University.

Dr. W. Garrett Owen is an assistant professor and extension specialist of floriculture, greenhouse, and controlled-environment crop production in the Department of Horticulture at the University of Kentucky.

In about 25,000 square feet of indoor growing area outfitted with LED (light-emitting diode) lights, Buckeye Relief in Eastlake, Ohio, cultivates medical cannabis for dispensaries in the Buckeye State.

The operation installed vertical grow racks but currently cultivates on one level, as it aims to expand along with Ohio’s medical-only market, says Jeremy Shechter, the company’s director of cultivation. (Ohio’s program launched in January 2019.)

“As the Ohio market develops—which we expect it to within the next probably 10 to 15 months—we have all of the electricity and all of the ducting and all the irrigation channels,” Shechter says.

Arguably the No. 1 benefit of cultivating cannabis under LED lights is that plants can grow on two levels without the hazard of heat stress, he says. Already, on its single level, Buckeye Relief has cultivated crops that have touched the lights and not burned. “The ability to grow vertical is huge,” Shechter says.

In the interim, the facility follows these lighting practices to cultivate quality cannabis indoors.

1. Install lights with 0%-100% dimming capability.

Cultivators using LED lights must be able to dim the lights by any percentage when their plants are stressed or when they need to make a foliar or pesticide application, Shechter says. This allows them to provide optimal light levels without wasting energy.

Not all LED dimming is the same, Shechter adds, so cultivators must connect “source” equipment, which provides a signal that gets modulated, to “sink” equipment, which receives a signal. For example, they can connect a sink fixture to a source control.

2. Run the grow a little hot.

Buckeye Relief keeps its grow room at 79 to 80 degrees Fahrenheit, 3 degrees above its leaf temperature of 75 to 77 degrees Fahrenheit, Shechter says.

“Just a simple rule of thumb that we've found is that leaf temperatures tend to be lower in LED rooms compared to HID [high-intensity discharge] rooms,” he says. “The difference between the air temperature and the leaf temperature is greater in LED rooms because you don't have that radiation from the lights heating up the leaves.”

Temperature directly affects yield, but cultivators should also pay attention to leaf temperature so they can avoid condensation on leaves. “If the temperature of the leaf drops below the dew point of the room, then you can have condensation on the leaf, and that obviously opens the plant up to pathogens, fungal issues, stuff like that,” Shechter says.

3. Integrate all environmental controls on a single interface.

Some cultivators piecemeal their environmental controls, with a thermostat here and CO₂ monitors there. “People really like to cut costs by not integrating all of their environmental controls together on a single interface,” Shechter says. “I think that's a mistake.”

Environmental controls affect each other, so cultivators should connect them, Shechter says. By doing this, they can graph their data and track it over time.

Patrick Williams is a senior editor for Cannabis Business Times and Cannabis Dispensary.

After several delays, representatives in the U.S. House voted to pass the Marijuana Opportunity Reinvestment and Expungement (MORE) Act in early December, a bill that would deschedule and decriminalize cannabis at the federal level. However, many believe its chances of advancing through the Senate are slim. Despite this, Charlie Bachtell, co-founder and CEO of multistate operator Cresco Labs, noted the symbolic significance of the moment. CBT spoke to Bachtell an hour after the U.S. House vote was announced to get his take on the MORE Act and how federal decriminalization would affect Cresco Labs, a company with 15 production facilities and 29 retail licenses across nine states.

Michelle Simakis: What came to mind first for you when you heard the MORE Act had passed?

Charlie Bachtell: While everyone likes to focus on the details and the specifics, it really is important for everyone to take a step back and say, “Wow.” The fact that cannabis legislation can be presented on the floor, receive a vote and get passed is fundamentally important for the continued development of a respectable and responsible cannabis industry in the U.S.

MS: What do you think is the most important aspect of the MORE Act?

CB: The MORE Act is important from the perspective of social equity and social justice. It goes beyond banking access. This is legalization with purpose. The fact that you’ve got, for the second time, cannabis-related language now receiving a favorable vote out of half of Congress is something that I know the pioneers of this industry, upon the shoulders of which we stand, didn’t know if they would ever see.

MS: What do you think finally helped push cannabis decriminalization forward, at least in part of Congress?

CB: The truly activated ... and organized approach to getting change in D.C. is a lot newer. I think it benefits from the time that we live in, the connectivity of people and accessibility to information and social media. When cannabis really started to transition from, you know, “wink, wink nudge, nudge” medical programs across the country to pioneering markets in California and Colorado to a second generation of highly regulated, compliance-focused programs that started to get developed around 2013 and 2014, you really saw a tidal wave of support.

MS: What would descheduling cannabis at the federal level mean to Cresco Labs as a multi-state operator?

CB: When we founded Cresco Labs, a couple of things were pretty obvious to us. Cannabis was on the path to becoming a consumer packaged good. [And] at some point in time, federally legal would mean interstate commerce, so it had to be a fundamental part of the way you developed your business. It’s why we focused on building brands that resonate with consumers and the distribution of those brands to the stores that we don’t own because that offers us the best long-term opportunity as this industry continues to develop and be more accessible and more diverse.

MS: What would you do first, should cannabis be decriminalized and descheduled?

CB: This industry is truly being built with one to one-and-a-half hands behind its back. Not having access to traditional banking and resources, let alone actual capital at a decent rate, makes it really hard to build a business, scale a business. You can put all of the regulatory nuances in place that will encourage more diversity and more inclusiveness, but if [cannabis companies] can’t get the dollars needed to actually rent a storefront, build out a storefront, hire people, buy inventory and operate a business, it’s not going to work. Having access to more traditional avenues for to capital is going to be really important from the startup to publicly traded organizations like Cresco Labs. Then this industry becomes a different ballgame.

This interview has been edited for length and clarity.