LOS ANGELES—Many professional growers face the same dilemma when looking to expand or open a new cultivation space: deciding on either a warehouse, a greenhouse or an outdoor grow. One of the biggest issues at the center of this decision is lighting. At the recent Cannabis World Congress and Business Expo held here, Paul Golden, engineer with Nexus Greenhouse Systems, spoke to a room packed with current and future growers. In a presentation steered largely by audience questions, Golden gave important insights into understanding how to measure light to determine its efficiency in cultivation.
Having worked with dozens of grow operations across the country, Golden shared some of the most common but easily corrected lighting mistakes that hinder cultivation efficiency. The first mistake is having lamps spread too wide, which wastes valuable energy in lighting the walls and floor with high-intensity light. Growers will often build their lighting plans based on the total size of the room, not on the area dedicated to plants. With a little bit of foresight, fewer lamps may be necessary if the aisles between plants are not calculated into the total lighting needed.
A second common mistake is hanging lamps too high. This problem occurs when a grower tries to compensate for a lamp’s tremendous heat by hanging it high above the plant, or not thinking creatively about hanging lamps down lower from a high ceiling. Not only does this spread the light too wide and contribute to the problem of lighting walls and walkways, it also reduces light intensity. To ensure that plants are getting the right amount of light, intensity should always be measured at the canopy. If heat is an issue, Golden recommends adding an air circulation system to keep hot air moving away from the tops of the plants. He also cited research from the University of Mississippi that the ideal room temperature for cannabis is 83°F.
For the more technical audience member, Golden also provided his two most important measurements of light:
Photosynthetic photon flux density (PPFD) is scientific standard for measuring the amount of photosynthetically active radiation that reaches a particular area in one second and is measured in micromoles per square meter per second (µmol/m2/sec). This is the amount of light a plant uses for photosynthesis that lands in a given square meter of space in one second. Golden stated that the cannabis plant saturates with light and can use no more than about 1800 µmol/m2/sec.
Measuring PPFD should always be done at the canopy to see how much light is actually reaching the plants. But it’s also a good idea to measure at the lamp, as well as at different points down the plant to see how much light is being lost, and how much light is making its way to the lower parts of the plant.
The second measurement is Daily light integral (DLI). This is how much light is hitting a plant over the course of an entire day; it’s measured in moles per square meter per day (mol/m2/d). This measurement is crucial during the different stages of the plant’s life cycle, since the needed DLI will change for a plant based on its current stage. Golden said keeping an accurate record of the DLI and watching the weather forecast are especially important in greenhouses that use supplemental lighting. By taking these steps, the grower can maximize the efficient use of free sunlight by using supplemental lighting only when necessary to reach the target DLI.
Golden also urged growers in every setting to record and maintain accurate records of lighting for their plants; this help maximize the harvest and increase the efficiency of their grows. By understanding the science behind the plant’s well-being, growers can feel confident in how to scale their operations when they are ready to do so.
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