Greenhouse Grower (GG): When a greenhouse grower is looking into growing hemp (CBD production, clones, young plants, etc.) in a highly controlled glasshouse/greenhouse environment, what considerations should he take into account when it comes to lighting?

Here’s a few things growers need to evaluate:

• Initial cost: Price per fixture and the number of fixtures
• Energy usage: Efficacy of turning electricity into photosynthetic active radiation
• Lifespan: The L70 rating, often reported as 70% of its initial output
• Bulb replacement cost
• Installation cost
• Shading of the fixture
• Uniformity of light plan
• Light quality, which Influences crop response

GG: Do the lighting requirements change depending on the end-use of the hemp?

Yes, however, the term lighting is broad and encompasses many facets of light. Generally, light intensity, light quality, and light duration are lighting’s three most important traits, which independently cause different responses in plants. If the intended end-use of hemp is for oil and shelf flower products, then all three traits are essential in driving high-quality and consistent secondary metabolite profiles (what can be extracted for oil). If the fiber is used for industrial applications, light intensity is the most important trait. However, all three lighting traits can be manipulated to influence plant growth and development to grow longer, more robust fibers in the stalk of the plant.

GG: Would there be different lighting considerations for a grower who is starting with a new structure versus a retrofitted structure for growing hemp?

Absolutely. When growers are building new structures, they can avoid being blindsided by the unforeseen limitations and pitfalls that a retrofit facility may pose. Building a brand-new facility is expensive but has many advantages. A grower’s lighting decisions will be influenced differently when evaluating a preexisting building versus a new facility.

Retrofits are limited by the preexisting physical structure (where lights can hang), amperage limitations for power, glazing material used for the walls and roof, existing building codes, and the weight limitations of the structure. A new structure will account for all these factors, saving the grower time and reducing production bottlenecks common in facilities that are not originally built for hemp production.

GG: If a grower could have a top of the line, dream set-up for lighting when growing hemp in a greenhouse setting, what would he need?

The dream set-up will be specific to each operation, and it will depend on the business plan, greenhouse structure, climate, and genetics. With that said, cannabis, including hemp, thrives under high light. A typical vine crop vegetable supplemental lighting application calls for a photosynthetic photon flux density (PPFD) of less than 300 µmol/m2/s, assuming we are implementing a long-day application (16 to 18 hours) in northern climates. This application translates to a daily light integral (DLI) between about 17 and 19 mols/day, which, when added to the natural DLI, is a total DLI of about 35 moles/day in low-light regions.

In hemp production, growers should optimize their lighting solution to a DLI significantly higher than 35 mols/day. However, when choosing your target minimum DLI, consider the facility’s location and natural solar radiation levels throughout the year. We have seen facilities in certain regions that require supplemental PPFDs of more than 400 µmol/m2/s.

GG: Do LED lights have advantages over HPS lights for growing hemp in the greenhouse?

LEDs offer numerous advantages over HPS lighting in hemp production, namely increasing production yields as well as reducing operating costs:

LEDs emit significantly less radiant heat compared to an HPS equivalent. Decoupling the heat and light enables the grower to control climate more uniformly and effectively. It also enables the use of light during periods of the day or year in which thermal loads of HPS could be prohibitive. This is particularly useful for a high DLI crop like hemp where current price points offer the opportunity to use LED light more often, increasing production yield. Additionally, LED lighting maintains consistency and quality of production throughout the year, ensuring a stable supply and minimizing seasonality issues.

Operating costs are addressed twofold: first with improved efficiency and second, with reduced fixture maintenance. LED fixtures are about 40% more efficient than HPS, therefore, the electricity bill associated with running comparable light levels will drop by about 40%. Also, HPS bulbs need to be replaced every 10,000 hours. LED fixtures do not use bulbs, but do dim over the life of the fixture, hence the importance of recognizing L70 lifespan. Ultimately, LEDs do not require replacement bulbs and the accompanying labor costs.

GG: What type of effects can lighting have on hemp?

There are a series of effects lighting has on hemp production that can influence certain plant characteristics. Let’s characterize light via three traits: light intensity, light quality, and light duration. Light intensity will dictate the pace of photosynthesis in hemp, which is directly tied to the rate of growth. The higher the light intensity, the faster the plant will grow (assuming all other environmental parameters are optimized).

Light quality (spectrum) will drive plant morphology and trigger certain responses in secondary metabolite production through the excitement of different photoreceptors found in the chlorophyll. Light duration (photoperiod) acts as a signal that can trigger either flowering or maintain vegetative growth in plants.

GG: Are certain hemp cultivars better suited to different types of lighting?

Most growing practices can cause different responses in various species as well as in different cultivars, deemed a cultivar specific response. Some cannabis genetics are bred in outdoor fields throughout the world, while some have been bred indoors for decades. With multiple new genetics hitting the market, we are starting to see different cultivation responses.

More cultivars are bred to tolerate high light, therefore producing higher yields and more secondary metabolites. How growers source genetics will greatly determine the quality and the proper strategies for maximizing the yield of those specific cultivars. Cannabis is pushing the limits of lighting further than any other crop grown both outdoors and indoors.

GG: What lighting challenges are you seeing greenhouse growers come up against when growing hemp

Maintaining consistent DLI year-round is a challenge. DLI directly affects hemp yield and secondary metabolite production. Growers need to maintain the same DLI they experience during their sunniest time of the year (typically summer) during their lowest light levels in fall, winter, and the beginning of spring.

Ensuring DLI remains consistent will ensure consistency in yield and secondary metabolite profiles. This is extremely important for growers to understand, as fluctuations in DLI will result in fluctuations in yield and quality of their end product. Fluctuations in DLI adversely affect yield and product quality, ultimately affecting the buyer experience and the grower’s overall revenue.

GG: What are some best practices for vetting out a reliable lighting supplier with trustworthy, reputable information?

Three principles come to mind when assessing the credibility of a supplier. The first is data: Does your supplier understand your crop, and do they have proven solutions in your segment or application? Next, you must assess the system’s performance over the entire facility: What are the lighting specifications, how were they developed (lighting design strategy), and how will the proposed lighting impact the financial performance of your business? Finally, quality is critical. Growers should invest with the assurance that the manufacturer will be able to stand by their products through the entirety of the warranty period, which is typically five years or more.

GG: What are two to three pieces of advice you would have for a grower who is looking to grow hemp in a highly controlled greenhouse environment?

From a lighting standpoint, the grower must develop an understanding of natural light levels and the percentage of light lost due to your greenhouse’s glazing material. From there, determine a minimum DLI target for the winter to achieve consistent light levels throughout the year and consistent crop yield and quality. Beyond light, considering the end use of the product is critical (e.g., extract versus industrial applications). Understanding the end-use will drive key decisions in genetic selection, processing, and extraction equipment.