Temperature, humidity and plant nutrition are among the environmental parameters that must be evaluated and potentially accommodated. Many lighting manufacturers, such as Fluence by OSRAM, work with growers to help them manage their grow rooms to adjust for LEDs.
Retrofitting with LEDs
Abhay Thosar, Fluence’s director of horticultural services, says he often sees growers who grapple with temperature and humidity changes when converting from HPS to LED lighting. HPS fixtures give off more heat than LEDs, he says, and cultivators who switch to LEDs could see a drop of up to 8 degrees Fahrenheit in temperature, which in turn affects humidity.
“The humidity needs to be adjusted because, remember, when using the HPS, it has so much of the radiant heat,” Thosar says. “Most of the time, you don’t have a high humidity in the room, and the reason for that is the heat from the HPS . . . was usually drying out that humidity, and you might have 50% or 55% humidity, and that was easy. But, now, switching over to LEDs, it’s a spectrum that optimizes the photosynthetic activity . . . and the plant is going to have higher transpiration and . . . that’s going to increase the humidity in the room.”
Thosar says growers need to ramp up their dehumidification and airflow to avoid bacterial and fungal diseases that can affect plants which are exposed to higher-than-ideal humidity levels. “You need to have much better air movement in the room—around the crop—in order to maintain that transpiration rate and also have a better airflow to avoid any spots where there’s a bit of humidity, again, in order to avoid some of the fungal or bacterial diseases that could happen within the plant.”
Temperature and humidity are also closely tied to vapor pressure deficit (VPD)—the difference between the amount of moisture in the air and how much moisture the air can hold when it is saturated. Thosar says many cultivators use VPD to optimize plant growth.
“Most of the growers like to steer the crop with the VPD,” he says. “They try to be in a sweet spot, and that’s why it’s important to maintain the temperature and humidity.”
Higher photosynthetic activity also means that the plants will have increased metabolic activity, he adds, which leads to an uptick in water and nutrients.
Growing media may also have to be evaluated and adjusted, Thosar says, as the plants more actively use irrigation and fertilizer. For example, if a cultivator uses rockwool, the size of the rockwool block may need to be increased.
Thosar and the rest of Fluence’s horticultural services team work with growers to help fine-tune their environmental parameters after installing LED lighting to optimize their crops based on their unique cultivars, growing media, light intensity, infrastructure, and more.
“We work very closely with the growers through the first two or three flowering cycles, so they can get a handle on how to optimize their use of LEDs and get the optimal plant production,” Thosar says.
Fluence also conducts trials with growers using side-by-side comparisons of HPS and LED lighting to help them decide whether LEDs are right for them—and which environmental parameters will need to be adjusted when making the switch at full scale.
Overall, Thosar says the biggest mistake he sees growers make with LEDs is maintaining the same environmental parameters that they used with their HPS fixtures.
“They are used to growing under the HPS, and that’s exactly where these mistakes come into play, just because sometimes they still keep managing the crop as if it were grown under HPS,” he says. “Those are the pitfalls that they need to avoid . . . Now they have changed the light source, [and] they need to change their thinking and make sure that they acknowledge the fact that this is not grown under HPS. If they keep that in mind, I think they can avoid most of the pitfalls.”
On the flip side, one of the biggest opportunities for growers when using LEDs is having better control of their environment overall.
“It gives us a much better control on how we want to ramp up the light, and not worry about the heat portion,” he says. “You can dial in the crop as you want.”
The HPS fixture emits a lot more radiant heat compared to the LED fixture. This would be to the tune of 50-55% radiant heat, compared to 15-20% radiant heat from the LEDs. Hence when we separate the heat and light component of the lights, we can steer the environmental or climatic conditions to optimize the crop productivity. During certain crop stages, if we can manipulate the environmental conditions but still would like to provide high light intensity, this would be feasible working with the LEDs and not with the HPS.
Designed with LEDs in Mind
Growers who choose to install LED fixtures from the start when building out their cultivation facilities also need to adjust their environmental parameters to accommodate the lighting.
Michael Ward, CEO and founder of Michigan-based Harbor Farmz, built out his 11,000-square-foot vertical grow with LED lighting because he says “the benefits outweigh the costs” when considering energy efficiencies and the rebates available through many electrical providers.
Ward and his team worked with mechanical, electrical, and plumbing (MEP) experts, who were able to do load calculations based on Harbor Farmz’s decision to use LEDs.
“All of those calculations should be made prior to even purchasing the HVAC,” he says. “If you’re late to the party and you’ve already got your HVAC put in, it’s going to be a lesser load on your equipment if you go LEDs versus HPS.”
Ward decided to build his facility around LED lighting due to the fixtures’ lower energy consumption, as well as improved yields and terpene profiles in the crop. Harbor Farmz usually achieves between 2.5% and 4.5% terpenes on all the flower it grows under its LEDs, Ward says. In addition, the company usually yields between 50 grams and 65 grams per square foot in its facility, with yields increasing each harvest.
After selecting the LED lighting, the Harbor Farmz team put its HVAC and dehumidification in place based on plant count and transpiration rate.
“We’re different than others when it comes to growing because of the fact that we’re vertical farmers,” Ward says. “We grow 22 feet in the air, we have three tiers, [and] we’re not just one big room. We’re small, tight rooms, and I can grow up to 324 plants per room on three tiers, so 108 plants per level on three racks . . . The actual configuration of the room will decide which HVAC you’re going to have to use.”
Once Harbor Farmz’s facility was up and running, ongoing adjustments were made to temperature setpoints as the team pushed the lights to the maximum intensity.
“As you dial up the [photosynthetic photon flux density] (PPFD) and the parameters in the room and push the lights and push the plants, you’re going to drive them in a direction that’s going to maximize your yields, maximize your potency and maximize your terpene levels,” Ward says.
Harbor Farmz is a success story when it comes to implementing LEDs and adjusting for the many variables throughout the grow process. Fluence continues to work closely with similar growers who wish to push the limits on what is possible with plants.
