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Growers, researchers learning how, where and when to use supplemental lighting

Before growers invest in supplemental lighting they need to determine the impact of natural light levels on their crops.

One of the things that University of Florida horticulture professor Celina Gómez tries to reinforce with growers when talking about supplemental lighting is the importance of the daily light integral. Daily light integral is the sum of photosynthetic light (photosynthetically active radiation) received by plants in a day. Gómez did a presentation on “Yield Responses to Supplemental Lighting” at the Northeast Greenhouse Conference in November.

“Solar DLI will determine the light intensities that growers need and for how long they will need to run supplemental lights or even if they need supplemental light,” Gómez said. “Growers should be aware of the DLI whether they are growing greenhouse vegetable or ornamental crops. It is one of the most critical factors.

“Fruiting vegetable crops have a fairly high DLI requirement, usually between 20-25 moles of light per square meter per day (mol·m-2·d-1). For most ornamental crops, the DLI won’t likely be more than 12 moles since growers are not trying to develop fruit.”

Celina Gómez, environmental horticulture professor at University of Florida, said knowing the solar DLI will determine a grower’s need for supplemental lighting.
Photos courtesy of Celina Gómez, Univ. of Fla.

Gómez said growers may find it difficult to determine the optimal DLI for various crops.

“This information isn’t the easiest to find and there can be differences between similar species,” she said. “Finding the optimal DLI can be especially difficult to find for uncommon horticultural crops. During my presentation I had one greenhouse grower ask me about the optimal DLI for potato seed production.”

While knowing a plant’s DLI is important, Gómez said it is just as important for growers to know how much light is being delivered by the sun.

“Knowing what a crop is getting from the sun will determine how much a grower is going to need supplemental light or if he even needs supplemental light,” she said. “A grower may benefit from supplemental light for only a few months or for most of the entire year depending on the crop and its DLI.”

More accurate light measurement

Gómez said one area where growers are making progress is how they are measuring light intensity.

“After so many years of talking about the best way to measure light that is useful to plants, growers are realizing how to more accurately measure light,” she said. “They realize the importance of monitoring the light intensity that their plants receive from sunlight.

“I expect that more growers have invested in quantum sensors to measure light intensity and if they are still using light meters they realize they have to be able to figure out how to convert those readings that makes sense in regards to plant growth. The growers are getting it and making the conversions from footcandles to other metrics like moles.”

Still learning about LEDs

Even though growers better understand the importance of DLI, Gómez said growers can still be overwhelmed by the choice of supplemental lights available, including high pressure sodium (HPS) and light emitting diodes (LEDs).

“Most growers don’t know exactly what specific wavelengths or spectrum or what light recipe are best for their crops,” she said. “In the case of LEDs, most growers are choosing white LEDs or a combination of colors like red and blue. When I started my PhD in 2011, most available LED arrays came in combinations of red and blue. More LED light manufacturers are adding wavelengths to their range, but most commercial LED units come with fixed wavelengths.

“Most growers don’t know which specific wavelengths work best for their crops. They are relying on what they are told by the LED manufacturers. If the growers know what they want to do with a crop, then the university researchers working with the LED manufacturers could be able to advise growers on what LED lights they should be using. It’s also going to be cheaper for the light companies to manufacture fixtures with a standard recipe than to try to come up with a specific recipe for every grower.”

Gómez said LEDs have been more widely adapted by controlled environment agriculture growers operating vertical farms and warehouse facilities.

LEDs have been widely adapted by controlled environment agriculture growers operating vertical farms and warehouse facilities.
Photo courtesy of Farmbox Greens

“While an increasing number of greenhouse growers are interested in LEDs, more of these growers are still using high pressure sodium lamps,” she said. “I generally don’t recommend that greenhouse growers switch from HPS to LEDs just yet. There is more information that needs to be determined for LEDs. HPS is the more established technology and greenhouse growers know what they are getting with these lamps in regards to light intensity, light quality and lifespan. When it comes to greenhouse applications, LEDs can still be considered a high risk technology for growers. Most greenhouse growers are still waiting to make the transition from HPS to LEDs.”

Additional LED research

Gómez said many of the research papers published about LEDs have focused on the effect of light quality or spectrum on several different crops.
“A lot of the plant responses are also affected and dependent on the intensity of light or light quantity– high light vs. low light,” she said. “Under different light intensities plants are going to have different responses. There is also the potential for differences in cultivar responses. Most growers are not going to use a specific red, blue, far-red, white, whatever ratio of light quality for one particular cultivar when they have hundreds of different cultivars in their production facilities.”

Another area Gómez said still has to be determined is the lifetime of the LEDs used in production greenhouses.

“This has to do with the greenhouse production environment where there can be high temperatures, high humidity and chemical application residues,” she said. “The life expectancy of a LED installed in a greenhouse in Alaska is not likely to be the same as the life expectancy in a greenhouse in Indiana due to the different environmental conditions within the greenhouses.”

Another area that Gómez said could use more research is the area of LED interlighting or intracanopy lighting.

“This is something that we were interested in when I was a student at Purdue University,” she said. “This use of LEDs even has potential applications in areas that have high light levels.

“There can be a lot of shading within the plant canopies of high wire crops like tomatoes, cucumbers and peppers, even if the light levels overhead are high. Research still needs to be done with intracanopy lighting and with the light quality of intracanopy lighting. The light quality for this intracanopy lighting may need to be different than the light quality for overhead lighting.”

Gómez said the use of intracanopy lighting could potentially provide light to those leaves that are shaded by the upper canopy or by neighboring plants.

Intracanopy or interlighting LEDs could potentially be used to increase fruit number, fruit size and fruit quality of high wire crops like tomato.

“Those leaves may be receiving low levels of light and not photosynthesizing so they are not contributing to the photosynthetic production of the plant,” she said. “There is the potential of using intracanopy lighting to increase the photosynthetic activity. We don’t know yet if that is true or if that is even going to make a difference in terms of production.

“We don’t know if the plants have already reached their maximum genetic potential. We may find out that there is increased photosynthetic activity with intracanopy lighting. The increase in overall production could include number of fruit and size of fruit. Another benefit is that a specific light wavelength could increase fruit quality. That could potentially be done with intracanopy lighting by placing the fixture close to the fruit clusters. In the case of tomatoes the levels of beneficial compounds like lycopene might be able to be increased.”


For more: Celina Gómez, University of Florida, Department of Environmental Horticulture, Gainesville, FL 32611-0670; (352) 273-4568;;

David Kuack is a freelance technical writer in Fort Worth, Texas;

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Algae Production Using LEDs at the University of Kentucky

Algae production could help reduce greenhouse gases

Researchers at the University of Kentucky are using a greenhouse and LED lights to study the feasibility of growing algae with flue gas from coal-burning power plants to reduce greenhouse gas emissions.

By David Kuack

Algae are considered a nuisance by commercial greenhouse growers. The warm, moist conditions that occur in greenhouses provide the ideal environment for algae growth.
Algae can be found anywhere these conditions exist, including floors, walkways, under and on benches, on greenhouse glazings and walls, in irrigation pipes and emitters and misting lines, on the surface of evaporative cooling pads and on the surface of growing media in containers and ground beds. Algae can also be a food source for fungus gnats and shore flies. But algae also hold great potential in the production of value-added products.
Even though algae are a problem for growers, these simple green plants hold great potential in the production of biofuels, fertilizers, cosmetics, fish and animal feed and other value-added products. Members of the algae program at the University of Kentucky in Lexington are looking at the potential of algae production to help lower the emission of greenhouse gases, primarily carbon dioxide, from the burning of fossil fuels, particularly coal.
Andy Placido, an engineer associate with the university’s Center for Applied Energy Research, said the restrictions on greenhouse gas emissions will only increase as environmental issues gain in importance among the public and government and regulatory officials.
Kentucky’s Department of Energy Development and Independence is always looking for ways to make coal cleaner because it is a big part of the state’s economy,” said Placido. “State officials know that there is eventually going to be some type of restrictions or tax on greenhouse gas emissions. Coal produces more carbon dioxide per energy unit than natural gas and other fuels. So officials are trying to evaluate the technology that is available to reduce greenhouse gas emissions.”

Algae Production with LEDs
This culture closet is equipped with LED lights and temperature
control. It is used to grow algae from a few milliliters up to
15-20 liters. The algae is then moved into a greenhouse for further
production under  higher light levels and warmer temperatures.

An ample source of carbon dioxide
While most coal-burning power plants in Kentucky have been equipped with scrubbers to remove sulfur dioxide and nitrogen oxides, Placido said little has been done to restrict the amount of carbon dioxide that is generated in the flue gas.
“We are going to be using post-scrubbed flue gas, which is going to contain about 12 percent carbon dioxide and not a whole lot more,” he said. “There is a minimal amount of sulfur and nitrogen. That is the reason we are looking at using the carbon dioxide because there aren’t any mature technologies for the capture of this gas. Right now, we are basically following the same route that occurred during the 1980s when these power plants were looking for the technology to capture the sulfur and nitrogen.”
If the research is successful in capturing and using the carbon dioxide, there is the potential to use some of the sulfur and nitrogen currently being removed from the flue gas by the scrubbers.
“We know that algae use sulfur and nitrogen in addition to carbon dioxide,” he said. “Algae might eventually allow for the scrubbers to be eliminated altogether.”

LED lights and a greenhouse
Placido said the algae culturing system starts in the laboratory where the algae are allowed to multiply.
“We work with the university’s Department of Biosystems and Agricultural Engineering which maintains the algae strains in beakers,” he said. “The algae are purchased in small vials and then cultured up to a few hundred milliliters.”
Placido said this is when he and the other researchers start to work with the algae in an in-house designed culture closet equipped with Philips LED lights.
“We are growing algae indoors with temperature control,” he said. “We are starting to bubble in 5 percent carbon dioxide to allow the algae to acclimate to a higher percentage of carbon dioxide along with the LED lighting as we prepare to move the algae into the sunlight. When there is enough algae that have acclimated (0.05-0.1 gram of algae per liter of water), they will be taken from the culture closet to the greenhouse. In the greenhouse, it will still be a temperature-controlled environment. We’ll allow the algae to grow in the greenhouse and once they become accustomed to the higher light levels and change in temperature, we will take the algae out to the power plant where it will be exposed to outdoor conditions along with the flue gas. That is our algae process chain.”

Maximizing algae growth
LED lights are being used 24 hours a day in the culture room to provide constant light. Placido said they are also looking at using the LEDs outside as a supplement at night and possibly during winter at the power plant so the algae continue to grow.
“During the night algae start to respire during which they release carbon dioxide and take in oxygen,” he said. “This is the reverse process of what happens during the day. By using the LEDs we can keep the algae growing for 24 hours or at least reduce the respiration process. Because the LEDs are very efficient, we expect more algae will be produced than the energy needed to operate the lights.”
Placido said algae split when they grow so production is judged on doubling time. Under optimum light and temperatures in the lab a doubling time of 12-24 hours is achievable.
“With the outdoor conditions we will have with the flue gas, we are hoping to have a doubling time of two to three days,” he said. “We would like to increase the growth rate, but that is going to take some nutrient work along with optimizing the light and temperature levels. Outside we’re at the mercy of Mother Nature.”
Placido said algae growth is much better with the LEDs in a controlled environment than outside under natural conditions. He said the difference in growth comparing inside and outdoor conditions has not been quantified.
“We have gotten much greater algae growth rates inside in the culture closet equipped with LEDs than outside or in the greenhouse even under the best days in regards to light and temperature,” he said.

Algae Production in Photo Reactors
Algae is produced in photo-reactors that can be placed inside or outside  of a  greenhouse.
 The ultimate goal is to build a large reactor adjacent to a coal-burning  power plant
that  will use the carbon dioxide given off in the plant’s flue gas.

Real world use
Placido said when the system is set up at the power plant, more flue gas will be produced than can be used to grow the algae. The flue gas will be pulled into the photo-reactor, which is a series of glass tubes on a steel frame, as carbon dioxide gas is needed.
“Once the system is saturated with carbon dioxide, the algae will be allowed to grow and then will be harvested. More carbon dioxide will be added as it is needed,” he said. “We know that our reactor isn’t nearly big enough to capture all of the carbon dioxide. The reactor we are using only holds about 2,000 gallons of water. That’s a good size, but nowhere near the size we would need to capture all of the carbon dioxide. We have estimated to capture all of the carbon dioxide from this one power plant would require a reactor that would cover 100 acres and take millions of gallons of water.
Placido said the power plant can provide an unlimited amount of steam to keep the water in the reactor tubes from freezing during the winter.
“During the winter with the sun’s heat during day the water temperature would stay above freezing,” he said. “With the steam from the power plant to heat the water along with keeping the water circulating continuously, that should be enough to keep the system from freezing. Then we would supplement the natural light with the LEDs if it was needed.”

Grower potential
Placido said there are some possibilities for commercial growers to produce algae and use algae in the future.
“That is our goal, to find out how we can improve the process for making fuel and how does that compare with other algae-derived products, such as fertilizers, animal feed, etc.,” he said. “Our end goal is to make biofuel. In the future the ideal situation would be for growers to produce their own energy source.”

For more: Andy Placido is Engineer Associate II, University of Kentucky, Center for Applied Energy Research, (859) 257-0223;
David Kuack is a freelance technical writer in Fort Worth, Texas,

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New Video Shows Hydroponic Greenhouse Tomatoes being Grown with LEDs

New Video on Growing Hydroponic Tomatoes in a Greenhouse with LEDs

In this video you will see first hand how a Ukrainian Glass Greenhouse Tomato Grower uses the Philips GreenPower LED Interlighting Module to increase production on their hydroponically grown crops.

Please notice that the Interlighting Module does not replace HPS lighting.  It simply enhances other light sources by allowing the lower canopy of the crop to continue to be photo-synthetically active.

Please send any questions you may have to

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AJ Both of Rutgers discusses LED Lights for Horticulture and Greenhouses

Best management practices for selecting LED lights

Development of testing guidelines will make it easier for light manufacturers and growers to compare LED systems.

By David Kuack

Growers are always looking at new technology for growing their plants faster, better and cheaper. One of the relatively new technologies that is gaining interest among growers and researchers is light emitting diode (LED) lighting.
So far, much of the research that has been done on LED lighting for plant production has occurred in Europe and Japan. More recently an increasing number of researchers and growers in the United States have begun to look at what benefits the use of LED lighting may have on both vegetable and ornamental plants. This research is focusing on different phases of the production cycle, including seed germination, vegetative propagation, the impact on flowering and increased photosynthesis.
Much of the LED research in the United States is being conducted by plant scientists. One research project, which has received funding from USDA, is a cooperative effort between researchers at Purdue University, Michigan State University, University of Arizona and Rutgers University. While some of this project’s studies are examining plant growth and development, one part of the project is focused on developing best management practices and guidelines for testing and selecting LED lighting.

LED Grow Lights
LED Grow Lights used in Cut Roses

Measuring LED performance
A.J. Both, an agricultural engineer in Rutgers University’s Department of Environmental Sciences, said his part of the research project addresses the challenges that any grower or consumer encounters when they look at LED lighting.
“There are many companies with products on the market today and they all have claims about lifespan, light quality and benefits,” Both said. “It’s very difficult to verify these claims independently. So every manufacturer can pretty much claim what it wants. There is no real standard or baseline that we can relate these statements to and say this makes sense or no this is too outlandish to even consider.”
Both said he and the other project researchers thought it would be worthwhile to come up with a standardized approach or procedure to measure LED lighting systems for greenhouse applications.
“This would be an experimental setup in a controlled environment where measurements would be made of electricity consumption, light output, light intensity and light spectral qualities,” he said. “We would develop a testing procedure to compare manufacturers’ products. We would then come up with some guidelines that would be provided to the industry. This would then enable both manufacturers and greenhouse growers to make comparisons between the lighting systems that are available.”

Making light comparisons easier
Both said the testing design that he is developing will allow manufacturers and growers to bring in light systems on which specific tests can be conducted related to energy consumption and other performance parameters. The tests will enable Both to evaluate the entire product.
He said all of the project’s researchers are planning to do tests on some manufacturers’ lights.
“It’s not going to be feasible to test every single unit that is available,” he said. “We are not like “Consumer Reports” that can do testing on a large scale and publish a lot of data. We will be selective in the number of systems that we will evaluate. We probably won’t test more than a couple dozen lights per year. We’re not planning to be in the business of running a commercial testing lab.”
Both’s goal is to develop a testing bank or testing set up within the next year and to start some initial testing as soon as the components are available.
“We will trial a limited number of lamps because the tests will require some time and some consideration as to what environmental conditions we want to test the lights under and the type of measurements we need to take,” he said. “Initially it will take more time and then as we get used to the testing procedures it will go more quickly.
“The testing that will be done is mostly for our own understanding and the ultimate development of guidelines or standardized measurement procedures. The industry, both manufacturers and growers, can use these standards to verify claims independently. Providing a set of guidelines the industry can follow and base their claims on will make it easier for growers to compare the different systems available.”

LED Interlighting Modules used in Greenhouse Tomatoes
LED Grow Lights used as Interlighting in Greenhouse Tomatoes

Looking at other industries
Both said the project researchers are looking at the lighting industry to see if there have been other guidelines or procedures developed. He said standards are being used in the architectural lighting industry and these will be looked at to determine if they have application to the guidelines being developed for the greenhouse industry.
“Of course, we want to take a look to see how much of those other industries’ standards apply to this particular application and to determine what changes we may have to make to really make it worthwhile for our industry,” he said. “Because we are an independent entity in this whole testing process, whatever we develop is going to be scientifically sound,” he said. “Hopefully the testing process will convince the industry, particularly the manufacturers, to voluntarily adopt these guidelines in their design and manufacturing procedures. They can also be used as a marketing tool for the purpose of gaining the acceptance of growers.”

Combining research results
Both said that by combining the information he collects with the findings of the plant scientists he is working with should provide growers with specific crop information.
“Determining which LED lighting is best for a particular crop is part of what the other project researchers are doing,” he said. “They are looking at it more from a quality aspect. What light wavelengths to provide, where to locate the lights in the crop canopy, what duration, and things like that. I’m looking at it from the standpoint of what type of lights need to be evaluated to make it clear to growers what choices they have and what system might be better for them depending on their operation.”
Both said the researchers plan to trial some of the systems that have potential at several grower operations. He expects to be involved with the grower installations for testing purposes and will likely be taking some measurements at these locations.

A learning process
Both said the history of using LEDs is relatively short and the challenges and benefits associated with their use are not yet fully understood.
“It is going to take some time to figure out for a particular crop what are the benefits and challenges of using LED lighting for photoperiod control or for photosynthesis lighting,” he said. “To expect our four-year project to discover everything there is to know about LED lighting is not realistic. We are going to need a lot more time as a research community to investigate all the issues related to LED lighting before the implementation can be complete.”
For more: A.J. Both, Rutgers University, Department of Environmental Sciences, Bioresource Engineering, (732) 932-9534;
David Kuack is a freelance technical writer in Fort Worth, Texas,

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