Algae is defined as a large and diverse group of photosynthetic eukaryotic organisms typically found in damp places or in water. Most algae are autotrophic in that they make organic compounds from simple molecules by taking in energy from the environment such as the sun. Algae play significant roles in aquatic ecology. Microscopic forms that live suspended in water are called phytoplankton, and provide the food base for most marine food chains. The most complex marine algae are seaweeds, while the most complex freshwater forms are Charophyta, a division of green algae which includes spirogyra and stoneworts.

Farming of algae, also known as algaculture, is on the rise globally. Algae contain high levels of oils, carbohydrates, sugars, and proteins, and can be used to produce renewable fuel, medical drugs, foods, and cosmetics. Algae are already widely used in food products, from baby formula to ice-cream, providing texture, stabilizing features, and important nutrients for health. Growing concerns regarding the emission of greenhouse gases have driven investment into algae production as a potential alternative fuel. In addition, the plastics industry has upped its demand for algae to produce biodegradable plastics. According to Allied Markets Research, the global algae products market is expected to generate $3.5 billion by 2025 with growth driven primarily by increased demand for protein-based nutritional additives for healthy foods. 

Similar to the challenges facing greenhouse food and flower growers that are reliant on the sun, artificial lighting is utilized in algaculture as a supplement to control harvest cycle time and product consistency.  Historically, lighting technologies used in algae production were high pressure sodium, metal halide, and fluorescents. Drawbacks of these legacy technologies are the inability to control spectrum and intensity, energy inefficiency, and hazardous chemicals could contaminate the algae. Recent developments in LED technology have made them the preferred lighting solution in many commercial operations. LEDs offer light output spectrum that can be optimized for penetration through water and photosynthesis, as well as being safer (no harmful chemicals) and more energy efficient. While the “best” spectrum of light is somewhat dependent on the specific algae being targeted, there are general principles that hold true. Like land-based plants, algae strongly absorb and process chlorophyll a & b (red & blue light).

Absorption spectra of a few algae are shown in the graph. Algae are typically submerged, so the light will need to traverse through some length of water before reaching its target. From the graph, red light is quickly absorbed by water. Blue light is more readily absorbed if the water contains an average amount of organic material. Through a long path of water, green light has the highest transmission

Taking into consideration algae absorption and water transmission, many algaculture farmers choose a full white light spectrum. Other considerations in choosing a light include water/dust resistance, commonly referred to as ingress protection (IP rating). If the lights are to be completely submerged or operated outdoors, they should have an IP68 rating (dust tight and waterproof). Frequently, a separate enclosure is constructed in which the lights are placed since there is a very limited selection of IP68 rated lights.

Thrive Agritech has delivered its LED lighting products to leading microalgae producer, NFusion Technologies, headquartered in Phoenix, Arizona. NFusion purchased the lights due to their optimized full white light photosynthetic spectrum, ease of installation and IP66 rating. Thrive’s lights grow algae to be used as organic soil fertilizer for healthier and more sustainable modern farming.  

Aquaponics is the integration of hydroponics – growing plants without soil – and aquaculture – fish farming.  It’s a symbiotic ecosystem that uses the waste produced by fishes as nutrients for growing plants. The fish waste is broken down by nitrifying bacteria initially into nitrites and subsequently into nitrates, which are absorbed by plants as nutrients. The clean water is then recirculated back to the fish tank and the cycle repeats (figure below).

Aquaponics provides for an efficient way of growing leafy greens and vegetables in an eco-friendly manner. For example, Aquaponics uses 90% less water than traditional farming, while simultaneously producing on average six times more yield per square foot. Operators of aquaponics facilities typically sell both the plants and the fish. Fish species commonly farmed include tilapia, salmon, bass, carp, brim, and koi. According to Zion Market Research, the global aquaponics market was valued at approximately $0.5 billion in 2017 and is projected to increase to $1.3 billion by 2024, representing a compound annual growth rate of 10%. Some of the key companies participating in aquaponics market include The Aquaponic Source, Aquaponic Lynx, Greenlife Aquaponics, Aqua Allotments, Backyard Aquaponics, UrbanFarmers, ECF Farmsystems, Nelson and Pade, My Aquaponics, and Ultrasonics Canada Corporation.

For plants to remain viable at an aquaponics farm, photosynthesis is required, which means there must be a source of light. Light can be natural (sun) or electric, or a combination of both. Frequently, aquaponics operations are located in greenhouses where natural sunlight is abundant. But during winter months electric light is used to supplement the sun to ensure plants continue growing at an ideal pace. There are several considerations when choosing supplemental lighting including the optimal lighting technology, spectrum, installation, reliability, and cost. LED technology has become a popular choice recently due to increasing energy efficiency and lower up-front cost. Other lighting technologies are fluorescent, metal halide and high-pressure sodium (HPS). While the initial cost of these other technologies is lower than LEDs, operating costs are substantially higher due to lower energy efficiency. In addition, fluorescent, metal halide and HPS have much higher heat content transmitted to the plant, which can cause yellowing or burning of the plant if the light source is too close.

Thrive Agritech recently supplied LED lights for aquaponics to BellaVita Farm in Brookeville, Maryland. The farm produces a wide variety of leafy greens, tomatoes, and microgreens for sale to nearby high-end restaurants.

Proper control of temperature and humidity inside a grow room can be the difference between success and failure. Grow room temperature directly impacts leaf surface temperature, CO₂ supplementation, relative humidity, transpiration rates and nutrient uptake – to name a few. Temperature control may appear as simple as setting a programmable thermostat; but of course, it’s more complicated than that.

Overheating forces plants to take up more water and then quickly transpire it, which can cause humidity overload when the lights go off. And a high relative humidity can lead to devastating problems like powdery mildew. During nighttime periods of plant respiration, lights are off, which typically reduces the grow room ambient temperature by 5-10 degrees. The temperature drop and high relative humidity frequently create a wet environment that approaches the dew point.

The leading strategies for controlling temperature and humidity in a grow room include ventilation and dehumidification, or some combination of the two.  Determining which strategy to implement depends on the prevailing type of heat in the room. When plants transpire, stomata open, releasing water vapor through an evaporative process that cools the leaf. Water molecules in the plant absorb heat and are converted to a gas – water vapor. Since there is a phase change during this process, the heat absorbed by the water molecules is defined a latent heat. The other type of heat is called sensible heat, which is heat that is either added or subtracted without a phase change.

For the case of an overheated grow room dominated by sensible heat, a simple method for lowering the temperature is ventilation. Ventilation can be used to lower both temperature and humidity. Passive ventilation techniques have been utilized for thousands of years, so the technology is proven and so are its limitations. The efficacy of ventilation can be subject to local climate conditions and can be challenging during CO₂ supplementation.

Dehumidification should be considered when cooling a grow room with excessive latent heat and corresponding high humidity. Latent heat converters (LHC) transform excess water vapor into liquid, which dehumidifies the air and converts the heat of condensation (latent heat) into sensible heat that can be used to heat the environment when needed. Ventilation can be reduced, which lowers heating costs and allows atmospheric CO₂ enrichment. In addition to converting “wet” heat to “dry” heat, an LHC can be a good source of clean, readily accessible water. Moisture from inside the grow room can be recycled and used again.

Electric lighting can be the dominant source of heat in a grow room. As we know, LEDs are more efficient than traditional lighting technologies – they convert more electrical energy to light and less to heat. Energy supplied to an LED that isn’t converted to light becomes heat that gets radiated into the air. In contrast, much of the heat generated by an HPS fixture is contained in the light beam in the form of infrared (IR) energy. The IR energy, which is absorbed by the plants, raises the leaf surface temperature and induces higher rates of transpiration. So, HPS lighting can lead to higher amounts of latent heat (via plant transpiration), while LED lighting creates more sensible heat by radiative heating. These differences can influence the strategies used to optimize temperature and humidity in a grow room.

In order to produce healthy and vigorous plants, it’s important to understand how nutrient efficacy can be affected by upgrading to LED lighting. Growers are frequently surprised to discover the light intensity and uniformity on their canopies aren’t what they thought. High-pressure sodium (HPS) and ceramic metal halide (CMH) lights degrade in intensity fairly quickly. And in many cases, the intensity and uniformity aren’t up to par even with new bulbs. In contrast, a properly designed and installed LED solution should provide the right light intensity with excellent uniformity across the canopy. Further, the spectral content of LEDs is different from traditional lighting technologies, and the change in spectrum may result in a variance in nutrient uptake by the plant. So how does this impact your nutrient strategy?

Drip irrigation using water-soluble fertilizers, otherwise known as fertigation, is a common practice in controlled environment agriculture (CEA) – see figure below. The primary goal of fertilizing is to augment the nitrogen uptake in the plant, which should enhance fertility and productivity. Since nitrogen is a gas, ammonium nitrate (NH₄NO₃) is used in powder/crystal form and combined with water to supply nitrogen to the crop.

When upgrading to LED lighting with different spectrum, intensity and uniformity profiles, fertigation strategies may need to be modified. We know that as light intensity (PPFD) increases, transpiration typically increases. Higher transpiration rates will pull more water out of the fertigation solution – leaving behind a relatively high concentration of mineral ions from the ammonium nitrate (nitrogen salts) in the media or root zone. This can make it difficult for the plant to take in water and nutrients, thereby creating nutrient imbalances.

The best way to ensure the ideal fertilizer concentration is to measure the pH and electrical conductivity (EC) of the nutrient solution and in the growing media. Since mineral ions in the fertilizer solution conduct electricity, measuring the EC is a perfect way to determine if the right amount of nutrients are being used to meet the needs of the plants without over fertilizing. It’s important to measure both the nutrient solution and the soil/media near the root zone to determine the salinity level of each. An elevated EC reading means a high concentration of mineral ions (fertilizer). If the EC reading is too high in the nutrient solution, the solution should be diluted with additional water. If the EC is too high in the soil/media, it is best to perform a leaching operation to bring it back into balance. The figure below shows a typical meter that measures pH and EC.

Likewise, measuring pH of the soil/media is an indicator of salt build up. Ammonium-based fertilizers will acidify soil, meaning the pH will increase. For most commonly grown hydroponic crops, an optimal pH range is between 5.5 and 6.5.

There are a number of factors that determine the ideal EC value for a grow operation including, crop species, light intensity, temperature and humidity.  However, some general guidelines for CEA grown cannabis are shown in the chart below. From the chart, the electrical conductivity, and hence the nutrient concentration, increases with increasing maturity of the plant. An EC meter measures electrical conductivity in units of millisiemens per centimeter(mS/cm).

An incorrect nutrient concentration during fertigation can cause plant leaves to discolor, which is the result of a toxic effect commonly referred to as “fertilizer burn.” In the extreme, over fertilizing leading to a salt build up at the root zone can pull water out of the plant and cause it to wilt and die. To ensure an optimal harvest, the nutrient concentration may need to be adjusted to accommodate changes in light spectrum, intensity and uniformity from a lighting upgrade.

Growers working in controlled environments strive to optimize the variables in their control to produce the highest yield and best quality products. These key variables include temperature, humidity, nutrients, light, and CO2. This article examines how switching to LED technology from older lighting technologies such as high-pressure sodium (HPS) could impact CO₂ supplementation.

First, some background on the critical role of CO₂ in plant development. During the Calvin cycle of photosynthesis, the plant enzyme rubisco enables carbon fixation, which ultimately results in CO₂ and water being converted into simple sugars (carbohydrates). The chemical reaction involving rubisco is temperature-dependent, so to optimize photosynthesis we need to understand the interplay between light, temperature and CO₂ concentration.

Looking at each variable independently in figure 1, we see that increasing light, CO₂ and temperature (leaf surface temperature) increases photosynthesis. There are clearly diminishing returns in the photosynthetic rate at very high levels of light and CO₂.

Interestingly, increasing temperature beyond an ideal point actually decreases the photosynthetic rate. This is attributable to the temperature dependence of the rubisco reaction – see figure 2. Without supplementing, the concentration of CO2 in ambient air is roughly 300 parts per million (PPM). Under these ambient conditions, the ideal leaf temperature is about 25°C.

If we add CO₂ to the environment, we can generate higher rates of photosynthesis at higher leaf surface temperatures – see figure 3.

So the key to CO₂ supplementation is to achieve the concentration where you begin to experience minimal additional photosynthetic production by adding more CO₂. That ideal concentration will depend on the light intensity and the leaf surface temperature – see figure 4.

The grower will ensure the leaf surface temperature is within a narrow window to achieve the required vapor pressure deficit (VPD). An optimized VPD enables maximal transpiration and photosynthesis.

The controlled environment agriculture industry is experiencing a shift in lighting technology. LEDs are rapidly displacing HPS, metal halide and fluorescent technologies. LED lighting has some unique characteristics that must be taken into account when upgrading a grow facility from older lighting technologies. LED lights typically have very little infrared energy in the beam, which reduces the leaf surface temperature. With a lower leaf temperature, the grower may choose to either decrease the relative humidity or increase the heat in the room in order to maintain the necessary VPD. And this decision is likely to influence the ideal set-point for CO₂ concentration. For example, if the leaf temperature is lower, the CO₂ concentration should be lowered to prevent working in the “dark-limited” phase as shown in figure 4. Conversely, if the grow facility can return the leaf surface temperature to its previous level, then an adjustment is CO₂ would not be required.

Although the ideal CO₂ concentration is a function of the plant species, light intensity and, leaf surface temperature, figure 5 presents typical CO₂ values for the various phases of cannabis development.

Maximizing biomass production in a commercial grow facility requires a deep understanding of the critical control parameters. While the benefits of LED grow lights are obvious, growers need to consider how the new technology impacts the canopy – especially as it relates to CO₂ supplementation.