Cultivating with LEDs: Past, Present, and Future: Page 3 of 3

April 4, 2019
Roger Kern
Roger Kern
Abstract / Synopsis: 

Driven by the need to save energy and reduce operational costs, indoor growers are turning to alternative means of illuminating their cannabis crop. In more and more indoor grows, high-intensity discharge lamps (HIDs) are being swapped out for light-emitting diodes (LEDs). The reasons to do so are numerous, not just energy savings, but the increasing ability to tailor the light spectrum for getting the most out of the plant. LEDs will play an important role in grows of the future, where networked lighting and environmental sensors are integrated into a comprehensive cultivation platform. The time to try LEDs is now.

Additionally, cultivators quickly may learn just how much their plants needed the radiant heat from the HIDs to grow as desired. Then it’s a matter of compensating by raising the air temperature in the grow room, although experts disagree by how much—or if it’s even needed. Dr. Daniel Hopper, chief cultivation officer at Nevada’s Silver State Relief dispensary in Sparks, Nevada, using Lumigrow lights, said when he compared plants grown in a room kept at 82 °F/27.8 °C with only LEDs versus 78 °F/25.6 °C, he noticed no difference. But Justice said to raise the plants’ temperatures she runs LED rooms warmer than rooms equipped with high pressure sodium (HPS) lights, perhaps into the low 80s during the vegetative stage.

Another factor often overlooked following a conversion is light intensity. After cultivators realize they’re no longer at risk of burning their plants from a too-close HID, some bring the LED right next to the leaves. This, of course, cranks up the PPFD—which some genetics can handle while others can’t. Justice said one of OutCo’s best strains, Grape Pie, starts to foxtail once the PPFD reaches 900 micromoles, and when the PPFD crosses the 1000-micromole threshold, the flowers start to change morphology and look “finger-y” and not as “trichome-y.” In fact, she noted, the resulting plant takes on a shade of brown, as if it was grown outdoors. However, the lack of aesthetics is made up for by a higher yield and greater potency. On the other hand, she added, the strain “Tangimal” can take 1200 micromoles without ill effect. You need to optimize each strain to get the most out of your LED lighting fixture.

Many growers find it is easier to over-water LED grown plants than HID grown. Growers often modify their nutrient formulations when growing under LEDs. The nutrient mix is often run at a higher mineral salt concentration (electric conductivity [EC]) than they were using before. Tom Haffly, director of production at Temescal Wellness in Worcester, Massachusetts, using Illumitex lighting, said he’s found success from increasing salt in the nutrient content, bumping EC from 2.0 to 2.7. Haffly also raises the carbon dioxide levels when using LEDs compared to HPS, going from 800–950 ppm to 1000–1200 ppm. While Haffly has seen some growers boost their CO2 levels to as high as 1500, he doesn’t believe yields increase once past 1200–1300 ppm.

Optimizing the spectrum during the vegetative stage can change the overall morphology of a plant that’s tall and lean, with a weak stem and not many leaves to a smaller more robust plant that is better suited to production. This can be accomplished by using a fixture that is relatively high in the blue part of the spectrum. During flowering, a relatively high level of red light helps the growth of large, dense buds. (Of course, if a cultivator is growing cannabis for a product that doesn’t need photogenic buds [for example, concentrates or edibles] then the absence of red light is not of consequence.) Silver State found that flowers given a “No Red” light treatment in the final three days of production showed an increase in terpenes with almost no effect on the final cannabinoid content.

But in a macro sense, different genetics simply react differently to LEDs versus HIDs. Hopper said his grow rooms with a “checkerboard” pattern of the two types of lights are good for the strains Bio-Diesel and Pineapple Express, while doing better in the all-LED rooms are, among others, White Widow, J1, and Durban Poison.

Haffly has his own lists of which strains do well under LEDs (Sour Candy, Jelly Sherbet, Blue Dream, as well as all Punch and Platinum genetics) and those that don’t (Super Silver Sour). But for the latter category, he notes, it may be less a matter of plants reacting poorly to LEDs than those plants needing different environmental parameters (for example, temperature, CO2 levels, and concentration of nutrients) while under LEDs.


Lighting the Path Forward

I expect over time the cost of LED lighting fixtures will continue to drop and, based on theoretical considerations, there is room for them to improve dramatically in efficiency. In short, LEDs are here to stay and I expect them to capture the lion’s share of the market in the not too distant future. But I expect these fixtures may evolve into more than just a light; we may be able to establish a fully-sensored lighting platform. What has me, and others, excited about LEDs is how they can be integrated into the grow rooms of the future. Imagine a set-up in which the lighting, irrigation, and climate control are networked with these fixtures that can also host tiny cameras and sensors surveilling every plant for wilting, foxtailing, mildew, pests, and other signs of distress. With everything connected, an alert can trigger an immediate and appropriate response by the cultivation system as a whole. With enough computing horsepower, such a platform can use the collected data to be predictive, enacting proactive solutions rather than reactive fixes.

Specific to lighting, LEDs will be finely tuned to direct cannabinoid profiles, with the goals of delivering consistent results harvest after harvest or bringing out compounds subtler than tetrahydrocannabinol (THC).

In my estimation, the time to switch to LEDs is now. If you are operating a facility, start by purchasing a few fixtures for one room and learn how to grow with them before embarking on a total conversion of your facility. Education is key, understand you will have to modify your environmental parameters: temperature, humidity, nutrient concentration, and watering rate. You may even want to change the strains you grow to optimize your production under LED lighting. In the end, this will result in energy savings and higher yields of more potency that will help your bottom-line grow.

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Dr. Roger Kern is a scientist and technologist who cares deeply about the cultivation and health of plants in the cannabis industry. With his PhD in microbiology from the University of California, Davis, Plant Growth Laboratory, he solves the most challenging problems in hydroponics, from studying the root microbiome to developing nutrients and lighting systems to ensure plant health and a disease-free lifecycle. He spent 22 years at NASA’s Jet Propulsion Laboratory as a scientist, technologist, and research leader before becoming the President of Agate Biosciences, a consulting firm for project management, systems engineering, and science in CEA for the past eight years. He leads developments to optimize sustainability, consistency, quality, and yield without compromising plant health. Direct correspondence to: [email protected]


How to Cite This Article

R Kern, Cannabis Science and Technology 2(2), 20-24 (2019).