Supplemental lighting latest

Photo: © xiaoliangge & Tasphong | Adobestock

In an August 2022 webinar, GLASE hosted a roundtable featuring the latest in lighting for CEA operations. Moderated by Haley Rylander, the director of the CEA group at Cornell University, the panel featured Cornell’s Neil Mattson, a professor at Cornell University, and GLASE director Erico Mattos. It also featured insight from five representatives of different lighting companies: Woody Smith, CTO at Vertaag; Louis Brun, CEO of Sollum Technologies; Brian Harris, technical sales rep for Hort Americas; Colin Brice, a horticulture plant specialist at Signify; and Sanaz Jarolmasjed, director of biological and machine vision systems at Agnetix.

Here are three takeaways from the webinar. The full webinar is available on GLASE’s YouTube page (bit.ly/GLASE-webinars).

What to know about light spectrum vs. light intensity

Mattson started off the webinar by asking the panel by asking each panelist to consider light spectrum vs. lighting intensity. Jarolmasjed answered the question first, noting that spectrum is especially important for growers in an indoor setting vs. a more traditional greenhouse setup.

“We are trying to copy what sun is providing to our plants,” she said. “In indoor settings, we want the full spectrum plus far red, which recent studies are saying we need to provide for our plants as well. Plants need that. Plants utilize that.”

The next question to ask, she continued, is how much of each part of the lighting spectrum is needed and at what intensity.

“When we come up with the correct spectrum for plants, we need to provide the right intensity based on the plants,” Jarolmasjed said. “Plants have a limit. But I think traditionally, we focus on how much light a plant can take.”

Brun, Sollum’s CEO, spoke next.

“I think [light] intensity is something that’s pretty well understood today,” he said. “The time is now to move fully to understand the impact of the different spectrums. We’ve seen the impact of the far red, for instance, on stem elongation. But we foresee learning more and how it affects plant quality and shelf life.”

Measuring light correctly helps maximize efficiency

Mattos asked the second question: What is the best way to measure light in an indoor/greenhouse setting?

Smith, the CTO at Verstaag, answered first, noting that his company’s technology uses five different sensors at five different frequencies to properly measure lighting.

“The ideal is to be in an open greenhouse setting where you can measure the sun’s impact on overall lighting levels vs. what is optimum for plant growth,” he said. “And then dynamically adjust that. So about every second, we adjust the sensors vs. what we are looking for in terms of spectrum and intensity. That varies over the course of the day. It does also depend on what stage a plant is in its growth cycle. There are spectrums that are optimized for the seedling stage vs. a more developed growth phase. That’s been the most efficient approach that we’ve found to this point.”

As for placing the sensors, Smith said the key is placing them where they can “see what the plants are going to see.”

“It’s a lot of data, but it works well,” he said.

Know your DLI and outputs

Mattson asked a question regarding lighting different crops. He noted that different crops have different requirements, so he asked if anyone is using any specific metrics/calculations for specific crops and how to work with growers to determine the amount of light they need.

Hort Americas’ Harris answered first. He said it’s important to start with the daily light integral (DLI) and work from there.

“When we start looking at yield per light, definitely know that different crops require different light,” he said. “That’s where we have to start. We have to look at crops being grown, the region they are being grown in. We start by looking at the lowest light levels and see what kind of light we need to efficiently grow through this low light periods.” Growers in Texas and Ohio, he said, will have different needs based on the time of the year even if they are growing the same crop in similar systems.

“It all comes down to the variables we have to control,” he said. “... It also comes down to cost effectiveness. Where do we draw the line between the capital expense to get more light and the operational expense of running those lights? And how efficient are the lights in general?”

Signify’s Brice said he was “lit up” to answer the question, noting that it’s the “bread and butter” of what he does on a day-to-day basis.

“What we see is that grams per mol is a powerful metric in terms of how much product you can produce per quantifiable mol of light,” he said, saying that metric is called “light use efficiency” among plant specialists. “It ranges widely not only by crop, but within different species and different areas.”

In North America, he said, there’s been a trend towards higher light intensity over low maturity lettuce crops. Growers, though, have to be careful.

“You just have to be careful to not overspend and not exceed what a plant can take in,” Brice said. “This metric sounds really scientific and heady, but it’s really important to understand the efficiency of your production.”