7 strategies to improve cannabis lighting

Whether growers are cultivating indoors or in greenhouses, intensity Is key to boosting yield.

According to the 2020 "State of the Cannabis Lighting Market" study conducted by Cannabis Business Times and made possible by Fluence by OSRAM, most cannabis cultivators are growing indoors, as 85% of participants said they operated this type of facility. However, an increasing number of growers also are running year-round greenhouses, as nearly a third (29%) indicated they grow in greenhouses with supplemental lighting.

Taylor Kirk, horticulture service specialist with Fluence by OSRAM, says while there are lighting fundamentals that apply no matter what type of facility growers are operating, there are certain strategies that indoor growers must use to be successful that are different than approaches greenhouse growers take.

"When you're in a greenhouse supplementing with LEDs or another source, you are basically working with what you have from Mother Nature with sunlight, and then figuring out what you could add to offset low light levels at certain times, like cloudy days or certain times of the year where you just don't get as much sunlight. And that becomes a lot more challenging because you have to take a holistic approach to how much light the plant receives in a given day," Kirk says. "With sunlight, you have sunrise and sunsets and this natural bell-shape curve of light intensity throughout the day, and there are a lot of different ways to manage it."

While most growers consider light spectra, or the quality of light, light intensity and photoperiod when planning lighting strategies, Kirk says one of the most important inputs for boosting yield whether growing indoors or in greenhouses is light intensity. Growers who dial up this parameter carefully can see higher yields and other benefits.

Here, Kirk shares seven lighting tips and strategies for cannabis cultivators, whether they are growing indoors or in greenhouses.

1. Optimal lighting spectrum varies by facility type.

While indoor growers rely on lighting fixtures exclusively, greenhouse growers receive some of their power from the sun. Because sunlight provides a wider spectrum naturally, greenhouse growers are often interested in options other than broad-spectrum light-emitting diodes (LEDs), Kirk says.

"There are very efficient fixtures that you can run in a greenhouse that are more red/blue leaning, giving you that pink light source," he says. "But since you're supplementing sunlight [in a greenhouse,] that works out. But we know for sure from all of [Fluence's] research that the best light spectrum for indoor cultivation is a broad spectrum, as white light is the best suited for indoor cannabis growth."

Broad spectrum lights provide a balance of blue, green and red light, mimicking the sun, with the exception of far red and UV light. "We've done some trials on far red and UV as well, and we just haven't seen the benefit that outweighs some of the downsides of it," Kirk says.

2. Lighting intensity plays a large role in maximizing production and yields.

As cannabis ages, it can take a higher amount of light, Kirk says. According to a recent light intensity study conducted by Fluence in partnership with Texas Original Compassionate Cultivation, research suggests growers can in some cases double the intensity traditionally used.

"We have some early successful data, and we have ideas of how much light this plant can take. It's pretty remarkable compared to other crops," Kirk says. "It's way more light than anything else can take."

"If you're really interested in pushing ultra-high light intensities to see this maximum yield potential from cannabis, you better be ready because everything that you're doing impacts that performance and that yield potential. It's not just how much light you're giving them." — Taylor Kirk, horticulture service specialist, Fluence by OSRAM

3. When increasing light intensity, take a cautious, steady approach, and remember to factor in genetics.

While some growers keep a constant light level in propagation, Kirk says cultivators can experiment with starting at a low intensity in this stage and increasing light gradually to better acclimate and prepare plants for more intensity in the vegetative and flower phases.

"We recommend 50 micromoles a day of increase in veg and about 100 micromoles a day in flower, but all of this is cultivar-dependent. And I do like to emphasize that because cannabis genetics are so diverse," Kirk says. "You have to be careful not to do it too fast because you can stress the plant and set yourself back and lower your yields. Some cannabis [cultivars] can handle a higher light intensity than others." 

4. Greenhouse growers must factor in DLI when increasing intensity.

All of this is cultivar-dependent. And I do like to emphasize that because cannabis genetics are so diverse." —Taylor Kirk, horticulture service specialist, Fluence by OSRAM

Daily light integral, or DLI, is a measure of how much light plants have received within the entire photoperiod, and it is measured in moles per day. Greenhouse growers use this measurement to supplement cloudy days and account for the natural cycles of the sun.

"The plant doesn't really care how the light is given, as long as that photoperiod isn't interrupted too much and they are getting a certain amount of light required for growth," Kirk says. "Indoor growers don't focus on DLI as much because typically they will provide the same amount of light for the entire photoperiod." (Although some growers use controls to mimic sunrises and sunsets, more research is needed to determine the efficacy of this approach, Kirk adds.)

Greenhouse growers need to factor in DLI when dialing up intensity. "If you have the same amount of light intensity given to the plant throughout that entire photo period, they're going to get more light in veg than they are going to be getting in flower at the same light intensity" because the photoperiod is 12 hours in flower versus 18 in veg, he says. "We typically increase the light intensity day one of flower a little bit, and that way, we're still decreasing DLI. Using an example here, say you're leaving the veg room at 500 PPFD, you would need to start at 750 in flower."

5. For growers using tiers, veg time is important.

Growers can adjust the time plants spend in the vegetative phase to help control plant size. While cultivators using tiered systems can also increase intensity, they must be careful not to let the plants spend too long in that lifecycle stage, Kirk says.

"You want to keep smaller plants, otherwise they are going to outgrow the space that you provide them," he says. "If you veg for too long, your plant is going to be pretty large when you initiate flowering and stretch even more. They always go through a growth spurt when the photoperiods change, so you need to keep plants shorter on a rack system."

6. Consider growing environment parameters when adjusting light intensity.

When dialing up intensity, growers must account and control for other factors, like temperature, humidity, irrigation and nutrients.

"The last thing we want to do is to tell a grower to use light intensity that's twice as much as they are historically used to using because we know we can get a lot more yield with that, but we're going to cause that grower to fail if we don't guide them through other factors that need to be adjusted, as well," Kirk cautions. "There are many factors that need to be managed carefully when you push the plant in this way."

The potential benefits are massive, as Kirk says growers can yield up to twice as much as commercial growers have historically yielded. That's why he and the horticulture service team at Fluence spend so much time coaching growers through the process of increasing intensity.

For example, vapor-pressure deficit, or VPD, is a metric they watch closely to be sure that intensity isn't negatively impacting the relationship between temperature and humidity. He suggests keeping the VPD in the "less stressful" ranges of .9 to 1.3 kPa. 

7. There's a direct correlation between increasing intensity and the need for increased nutrients and water. Be sure to feed and irrigate plants more.

Growing environment isn't the only parameter that must be considered when adjusting light intensity, however.

"The program that [growers] run, all the cultural practices, what kind of media they are using and fertilizer and concentration of fertilizer—all of these things need to be looked at if you're thinking about increasing light intensity," Kirk adds.

When growers provide the plant with more energy from light, they must supplement nutrients and water as well. However, each cultivar has different needs.

"I like to compare it to a bodybuilder. Normally, humans need probably 2,000 calories a day, and that's your average diet, but if you're a bodybuilder, you're not going to be able to see the results that you're after with 2,000 calories a day," he says. "So you're going to need to increase your concentration of calories and nutrients." Kirk says the same goes for plants, as they need increased inputs when receiving more light.

Although the "meat, potatoes and vegetable" nutrients plants need like potassium, magnesium and calcium are key, nonessential plant nutrients also are important to help plants tolerate more intensity.

"Earlier research was done with soilless mix that had quite a bit of organic amendments and biostimulant additions. It wasn't just fertilizer and water in a sterile environment [but also] the plant and microbial relationship as well, and there's a lot of benefits in there that reduce stress," Kirk says. "I definitely encourage the use of biostimulants."

Amino acid and fulvic acid may be non-essential additives, for example, but they can be beneficial, especially when increasing intensity.

"If you're really interested in pushing ultra-high light intensities to see this maximum yield potential from cannabis, you better be ready because everything that you're doing impacts that performance and that yield potential," he says. "It's not just how much light you're giving them."

Source and Photo Courtesy of Agritech Tomorrow

Source: Agritech Tomorrow