Horticultural Lighting Conference chronicles LED impact on food supply (MAGAZINE)

MAURY WRIGHT reports that the inaugural Horticultural Lighting Conference packed the house and featured experts from the research, grower, and SSL manufacturing sectors sharing the latest knowledge on the use of LED technology in boosting crop production.

LEDs Magazine's inaugural Horticultural Lighting Conference took place on Oct. 12 in Chicago with a full day of presentations to a packed room. In the evening an equally-crowded exhibit area provided quality networking time. The program focused on the history, present, and future of LED usage in horticultural applications, and the roles of solid-state lighting (SSL) to speed crop cycles, impact flavor, and control pathogens, all while saving energy relative to legacy sources. Here we will review the messages from three of the featured speakers.

Purdue University's Dr. Cary Mitchell.

Interested in articles & announcements on horticultural lighting?

Cary Mitchell presented the opening keynote. Mitchell is head of the horticulture program at Purdue University and has also directed NASA research on the use of LEDs. "It's been a little more than a quarter century since the LED plant growth story began," said Mitchell. Ironically, the work began before the advent of high-power white LEDs. But only in the last few years has the combination of technology development in LEDs and understanding of how plants respond to LED lighting advanced, leading to more widespread deployment of LED-based horticultural lighting or what is also known as CEA (controlled environment agriculture).

NASA and LED horticulture

The original work was NASA driven, seeking ways to grow food for space applications and perhaps a Mars mission. The space agency had realized the enormous energy burden that CEA would place on a mission if legacy lighting were used. Mitchell said, "It wouldn't work. You couldn't get enough energy to do it." The realization led NASA to look for narrow-spectrum sources; as Mitchell said, "You didn't have to use the less-efficient wavelengths or you could do away with the wasteful ones."

Mitchell said at the same time, he and others were researching growing food products in a very-high-density crop stand because space applications would inherently be limited in terms of the usable footprint available for CEA. But ultimately increasing density would lead to yield loss at some point, with the inability to get light through dense upper canopies becoming a problem. Mitchell led a project that showed what he termed "intra-canopy lighting" (often called interlighting today) could solve the problem, using a 15W fluorescent tube between plants. But even that source created other issues, such as generating heat that could potentially harm leaves. And the system was bulky, taking up room where plants could be growing.

To advance CEA, researchers needed a smaller source that did not produce heat and that could produce narrow spectrum. Mitchell said, "I was aware at the time that NASA was sponsoring work with LEDs, and I thought for a number of reasons that LEDs could be really good for this." In addition to solving the issues mentioned previously, he knew that LEDs as solid-state devices would be more reliable and have longer lifespans.

LED lightsicle

Twenty years ago, Mitchell created what he called an "LED lightsicle." The inspiration was a cross between a popsicle and a fluorescent tube. Mitchell intended the linear LED lamps to be hung vertically in a crop stand with the individual LEDs in the lamp controllable. The control enabled only the LEDs that were producing beneficial light to be powered on and use energy. For example, when plants were in an early growth stage the LEDs at the top of the lightsicle were powered off. Moreover, the design included LEDs of varying color so the control included the energy spectra applied to the plants.

Mitchell has also performed significant research in larger-scale applications such as in greenhouses for high-wire tomatoes. Indeed, he scaled the size of his lightsicle design to provide interlighting for tomato plants grown to heights greater than 10 ft. In such commercial tomato growing applications, workers harvest the fruit from the bottom up and then strip off the leaves from the bottom up. The controllable LED lighting at that lower part of the vine would not subsequently be used during that specific crop cycle.

Leafy greens

Closing the keynote, Mitchell discussed overhead lighting for hydroponic crops such as leaf lettuce. Again, the research was funded by NASA with the intent on fast crop cycles and low energy usage. The research yielded lettuce crops in 21 days.

Robert Colangelo of grower Green Sense Farms.

Mitchell moved on to describe how his work in the leafy green area has differed from practices that are prevalent in commercial vertical farms. He said most such farms have constant or even spacing in the layers and specifically between the plants and the overhead lighting. But he said because of the inverse square law that characterizes how light energy decreases with distance from the source, it is clear that you can use less energy by varying the distance between the top of the plants and the overhead lighting. Mitchell termed the technique close-canopy LED lighting and considers it analogous somewhat to intra-canopy lighting. Indeed, he placed lights within 10 cm of the lettuce, achieving power density of 160 W/m².

Mitchell also documented how the lettuce reacts during the crop cycle and how that knowledge can deliver further energy savings. We have regularly discussed evolving theories that suggest different spectra can optimize plant growth during different phases of the cycle. But Mitchell said a crop like lettuce goes through a lag phase of around 15 days where high light levels or different spectrum seem to have little or no effect on the crop. He suggested that lighting be set to minimal levels during that phase and then turned to higher intensity during the exponential growth phase at the latter part of the cycle - again, trying to minimize energy used while still optimizing yield.

Commercial grower

Robert Colangelo was the featured lunch speaker and addressed the state of the vertical farming sector and how what he described as a nascent market is evolving. Colangelo is the CEO and founding farmer at Green Sense Farms; we also covered that farm in our recent feature article on horticultural lighting.

Plant pathologist Dr. Jaimin Patel, LRC.

Colangelo said, "The indoor vertical farming market is emerging. It's new. I see it as the beginning of the beginning." Colangelo believes the market offers a tremendous opportunity, although he also described the market as fragile, adding, "It offers a lot of opportunity and the ability to shape it."

Evaluating a market sector, Colangelo said he likes to track the money flow through the market or business stream and figure out "who is the fish food in the room." He said, "The buyers are at the top of the food chain." In that group he places grocers, produce companies, restaurants, institutional food buyers, and food processing companies. Colangelo doesn't discount the impact of the individual consumer because the consumer does dictate the products that are consumed, but consumer choice is largely dictated by the buyers of large volumes of produce.

Second in the food chain are the growers, including vertical farms such as Green Sense. Colangelo said the second tier covers a broad range of small to large operations and even research farms. He also includes traditional greenhouses in the second tier.

The third tier consists of the suppliers, vendors, and consultants that support the growers. That group would include lighting manufacturers within a myriad of other types of suppliers ranging from fertilizer specialists to vendors offering hydroponic products to electrical product suppliers. The last tier consists of the publications, associations, and academia. These third and fourth tiers are engaged in helping the growers deliver consistent, safe, reliable produce.

Colangelo said growers must understand the value chain to succeed. Moreover, he noted that successful growers will need a broad skillset. Many smaller growers have moved into the sector, seeing it as a low-stress and rewarding way to make a living, but Colangelo warned that it is hard work. And growers need significant business acumen to succeed. At the other end of the spectrum, big business is trying to enter the sector but often lacks the growing skills and passion that are also necessary for success.

Plant pathogens

The last speaker at the Horticultural Lighting Conference was Jaimin Patel, a well-known plant pathologist who recently joined the Lighting Research Center (LRC) at Rensselaer Polytechnic Institute. Patel presented the Closing Plenary on behalf of himself; Mark Rea, the LRC director; and David Gadoury of Cornell University. The trio is working on a US Department of Agriculture-funded project studying the use of light to suppress plant pathogens.

Patel began by echoing a theme that had sounded throughout the day, noting that spectral control inherent in LEDs was delivering tremendous advantages in energy savings for horticulture. And he said the industry was moving beyond accelerating crop cycles to increasing nutritional value, improving or enhancing the flavor of produce, and changing the shape or look of plants.

But he quickly turned his attention to pathogens that challenge crop production and even the safety of the food supply. He said greenhouses and high-tunnel systems provide very favorable environments for epidemics of powdery mildews and other common diseases. He reminded attendees that such diseases can cause catastrophic losses, especially for individual growers.

Fungicides and pesticides

Growers have traditionally turned to chemicals such as fungicides or pesticides to battle pathogens. But application of such chemicals can leave residue on produce. Moreover, the pathogens quickly evolve to be resistant to treatment. Patel believes that light, when applied correctly, can fight the pathogens without any harmful effects.

Patel presented a number of examples of plant types and pathogen challenges, starting with strawberries and powdery mildew. Research showed that application of ultraviolet (UV) light could reduce the severity of a mildew attack from the 20-30% range to well below 5% and approaching zero. In the study, UV impact was tested at different power levels, durations, and frequency of application. In some cases, the UV light was only applied once every three nights, and those tests showed the highest severity. Treatments applied every night reduce severity slightly, although there is no clear indication that higher power levels have an impact and Patel said more work is needed.

Indeed, the challenge moving forward is clearly the research needed. Every plant is different in terms of the specific pathogens that are of concern and the stages of fungal growth in which some sort of treatment is required. But Patel wrapped up the conference saying that although diseases will remain part of the controlled environment, lighting can be an organic alternative to pesticides.