EDITORIAL DIGEST LED-based horticultural lighting plants ... · EDITORIAL DIGEST LED-based horticultural lighting plants

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EDITORIAL DIGEST

LED-based horticultural lighting plants the seeds for successful grow operationsSolid-state lighting (SSL) technology delivers

control and tunable spectrum benefits that

can enhance and improve plant growing

operations, especially in new operations

outside of the typical farming community.

This editorial digest combines the latest

information on science-backed horticultural

studies, a close look at photometrics and

energy-efficiency criteria for horticultural

lighting, and a detailed insider’s guide to

comparing and selecting appropriate fixtures

for project specification.

2 LED efficacy, UV, and plant feedback highlight horticulture presentations

12 Understand energy efficiency of LED horticultural lighting systems

21 Buyers benefit from LED grow light guidance

Reprinted with revisions to format from LEDs Magazine. Copyright 2018 by PennWell Corporation

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LEDs Magazine :: EDITORIAL DIGEST :: sponsored by

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* This article was published in the February 2018 issue of LEDs Magazine.

LED efficacy, UV, and plant feedback highlight horticulture presentations

The second US Horticultural Lighting Conference was packed with informative presentations, reports MAURY WRIGHT, with prevailing themes including SSL comparisons with legacy lighting, the use of ultraviolet spectrum to boost secondary metabolites, and the future of horticultural lighting.

IN DENVER, CO on Oct. 17, 2017, many of the foremost experts in the area

of horticultural lighting gathered at LEDs Magazine’s second annual US

conference on the topic. The day was packed with informative talks and

the networking in the tabletop exhibits and at the evening reception was

fast and furious. Here we will highlight a few presentations that looked at LED

lighting relative to alternative light sources for plants, ultraviolet (UV) lighting as

a way to sculpt the flavor or potency of cultivars, and future efforts that might

take feedback directly from plants to control the lighting applied.

Before we get started,

we will suggest that you

peruse some past content

if you aren’t familiar with

the concepts that underlie

FIG. 1. Petunias exhibit differences when grown in a greenhouse under no supplemental lighting (left), HPS supplemental lighting (middle), and LED lighting (right).



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LED-based horticultural lighting. An article that we ran last year examined solid-

state lighting (SSL) in the horticultural role, and contemplated key metrics that differ

from those used in lighting for humans. And coverage of our 2016 Horticultural

Lighting Conference provides insight into many issues surrounding the burgeoning

application. Moreover, Philip Smallwood, director of research at our Strategies

Unlimited market research business, opened the conference looking at the challenges

of the application and at

market data. For a limited

time, a webcast that reprised

that presentation is viewable

on demand.

The keynote presentation in

the opening session at the

conference came from Steven

Newman, the greenhouse

crops extension specialist

and professor of floriculture

at Colorado State University

(CSU). Newman had been

given a unique opportunity

to oversee construction of the

new CSU Horticulture Center

a few years back when the university built a new football stadium on the site of the

old facility. The project included more than 21,000 ft2 of greenhouse space, more

than 6000 ft2 of classroom space and a 6-acre outdoor gardening area.

As the new facility was being planned, Newman described how a chance meeting

with Philips Lighting led to the greenhouse facility being equipped with LED-

based Philips GreenPower Toplight luminaires despite the fact that Newman had

no prior SSL experience.

In spite of objections from the university engineering department that also had

no experience with LED lighting, Newman went forward with the SSL installation

based on the economics. Newman offered the data in the nearby table at the

conference, where the projections indicated that LED lighting would cost a half-

FIG. 2. Peter Barber of SETi explained how UV lighting can impact the production of secondary metabolites in plants, affecting flavor and other qualities.


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cent per day per square foot to operate and the high-pressure sodium (HPS)

alternative would cost more than a cent and a half. Newman said, “That tells me

the return on investment is faster than you think.”

LEDS AND FLORICULTURE

Newman said he welcomed

the next phase of his career

as a chance to learn about

working with LEDs and set

about to study “What could

we do with floriculture plants

to speed the production?”

Newman said he has already

studied a number of bedding

plants, but described one set of

tests in particular that directly

compared 600W LED lighting

with 1000W HPS lighting. He

said the HPS lighting delivered

PAR (photosynthetically

active radiation)-band PPFD (photosynthetic photon flux density) of 65 μmol/m2/

sec compared to 84 μmol/m2/sec for the LED lighting - with variables such as bench

height, temperature, and on/off cycles for the lighting held constant. Newman took

measurements at night to ensure that the PPFD levels were accurate with only a

security light providing in the range of 0.47 μmol/m2/sec in stray light.

The cultivar studied was the Bada Bing Scarlet variety of begonia. Newman

showed side-by-side photos of plants grown with no supplemental light, with the

HPS supplemental light, and with LED supplemental light. The plant that was

grown with HPS light was considerably smaller than the other two. Newman

classified it as suffering from “stunting.” He said he could not explain the

impact for sure, but speculated that it may have been due to the spectral power

distribution (SPD) of the HPS lighting.

The plants grown with no supplemental lighting and with LEDs appeared about

equal in height. But the plants grown under the LED lighting appeared more dense.

FIG. 3. LESA’s Tessa Pocock projected a future in which sensors would enable a closed-loop system for horticultural lighting where plants would tell the system what they need.



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Next, Newman showed similar photos of TriTunia Pink Veined petunias (Fig. 1).

In this case, the plant grown with no supplemental lighting was clearly taller

than the one grown under LED lighting, but Newman cautioned that a closer

look was required to discern the superior plant. Newman said in this case, the

compactness of the plant grown under LED lighting compared to the stringiness

of the plant grown with no supplemental lighting means that the more compact

plant is more likely to survive the trip through big-box retail to successful

transplant into a consumer’s garden. Meanwhile, the plant grown under HPS had

no evident flowering whereas the other two each had nice flowering.

NAPA VALLEY OF BEER

Newman then described another surprising crop being grown in the facility. Early

on in his talk, he had touted the Fort Collins area (home to CSU) as a great place

to visit with one reason being the prevalence of 23 craft breweries. He called the

region “the Napa Valley of beer.” We will let others debate that characterization,

but Newman’s CSU colleague Bill Bauerle is growing hops hydroponically for the

local brewing community.

Newman rhetorically asked, “Why grow hops in a controlled environment?” He

immediately admitted that it could not be as economical as outdoor growing

operations in Oregon and Washington that are using 25-ft-high trellis systems

with machine harvesting and an automated drying process.

But Newman said every time hops are touched by a person or equipment, the

quality goes down and the essential oils of the selected plant are compromised.

He said brewers cherish the flavor profile of the minimally-processed fresh or wet

hops and will pay a premium for that product to differentiate their beer. Moreover,

Newman said the economics work out better than you might think with the LED

lighting enabling continuous production and as many as five crop cycles per year.

UV LEDS IN HORTICULTURAL LIGHTING

Among the most compelling of presentations at the conference was a talk

focused on the use of UV spectrum in horticulture. Peter Barber (Fig. 2), director

of product marketing and business development at SETi, presented “The myriad

ways that UV LEDs will impact society through horticultural lighting.” SETi

is a UV technology specialist that was acquired by Seoul Viosys in early 2016.



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Seoul Viosys is focused on UV LEDs and is a sister business to visible-light LED

manufacturer Seoul Semiconductor.

Barber briefly discussed lighting in the PAR region before jumping into the UV

topic with the proclamation that UV energy has applicability over the complete

cycle of vegetable growth and consumption, or what he termed “seed to belly”

with the farmer of course in the middle of the cycle. Seedlings can benefit from

UV energy in two ways, according to Barber - UV treatments can strengthen root

systems and can prevent or suppress mold.

For the farmer, mold suppression remains a UV benefit, but there are many

additional benefits. As we have covered previously, UV energy can influence

the appearance, smell, and taste of plants. Indeed, UV energy can increase

nutritional value or perhaps potency in the case of a cultivar such as cannabis,

according to Barber.

There are secondary uses for UV lighting in a farm as well. For example, it can be

used to disinfect hydroponic lines that feed water and nutrients to plant roots. We

covered such a usage in a shipping-container-based vertical farm. UV exposure can

also increase the shelf life of products after harvest, benefitting the farmer and the

consumer. Barber said UV light can even be used to treat mold spots on produce.

SECONDARY METABOLITES

Still, it’s the impact on the look, flavor, and potency of a plant that may be the

most interesting result of UV light in horticulture, and Barber explained some

of the details of plant physiology relative to UV exposure. In response to UV-B

spectral energy (UV-B is the middle UV band spanning 280-315 nm), a plant reacts

through a stress mechanism to protect itself. The Mitogen-Activated Protein

Kinase signaling - MKP1/MPK3/MPK6 - initiates the response.

A molecular signaling pathway called UVR8 then is responsible for increased

secondary plant metabolites such as flavonoids in vegetables or THC in cannabis.

But the plants are very selective in terms of the spectra to which they react.

Barber used the analogy of an arcade skee ball game where the inner targets

deliver more points to the player than the outer targets.


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Barber said UV emission in the range of 280-300 nm only requires a fluence

rate of 0.1 μmol/m2/sec to achieve the desired boost for secondary metabolite

production. A plant would need ten times more energy from emission in the 301-

310-nm band. Barber said, “That’s why LEDs are so preferred. You can provide

that targeted region.” That statement could apply to LEDs in the PAR and other

bands as well as to the UV energy that Barber was discussing.

The mechanism by which the plant reaction occurs is due to a plant’s epigenetic

memory, according to Barber. As an example, he said cannabis grown at high

altitude in Colorado has higher concentrations of THC and terpenes than do

plants grown at sea level. The plants grown at higher altitude get more UV.

Barber likened the plant reaction to a natural sunscreen. And he pointed out that

sporadic exposure can trigger the reaction. Conversely, too much exposure can

lead to cell death. Barer said the closer you get to 280 nm, the greater the risk for

permanent damage, noting that “UV-C is unbiased when it comes to DNA” and

that it would destroy cells.

CLOSING PLENARY

The final talk at the conference was the Closing Plenary and it included some

data from studies on effective spectra, but more importantly it looked into the

future of horticulture. The speaker, Tessa Pocock, is certainly equipped with the

knowledge and experience to provide a forward look. Pocock is a senior research

scientist at the Center for Lighting Enabled Systems and Applications (LESA) at

Rensselaer Polytechnic Institute. LESA is a National Science Foundation (NSF) lab

with US government funding, and as such is charged with looking at technologies

that might come to fruition as much as a decade in the future.

Pocock opened by saying, “I’m a plant physiologist and my main concern is the

plant.” She said there have been around 400,000 species of plants characterized

in nature, yet only around 30 species are cultivated for food. In contrast, she said

around 21,000 taxa are used in pharmaceutical applications, so the horticultural

lighting application may be far larger than the food supply.

Lighting is critical in more ways than you might think for plants. Pocock said,

“Lighting is the primary information source for the plant. It tells the plant what to do

and when.” Moreover, she said light cues the plant as to what to expect and do next.



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Pocock said there are more than 100 plant genes and 26 biochemical pathways

that are regulated by light. She explained that photoreceptors in plants are quite

often discussed but the chloroplasts are elements in plant physiology for which

the details are often ignored.

PLANT’S SENSOR NETWORKS

Photoreceptor control has mainly a developmental impact on plants including

things such as flowering, photoperiodism, leaf expansion, and stomatal opening.

Chloroplasts are critical to

photosynthetic control and the

operation elements of plant

growth including light capture,

photosynthesis efficiency, CO2

assimilation, and protection

mechanisms and memory.

There are also elements of

plant growth that are shared in

terms of impact by the separate

photoreceptor and chloroplast

networks. Examples include

circadian rhythm, height, pigments, immunity, and defense. And Pocock said

the separate networks could in some cases combine favorably in terms of such

impact or in other cases oppose one another in terms of impact on the plant.

Pocock quickly got back to a detailed look at some plants that would make the

complexity of lighting impact clear. First, she showed the red lettuce called

Rouxai grown under four different types of lighting - a commercial LED fixture

with red, blue, and white LEDs (R/B/W), a phosphor-converted white LED (PC

LED), the lab’s basic reference cool-white fluorescent lamp (CWF), and a fixture

with red and blue LEDs (R/B LED).

The lettuce grown under the PC LED spectrum was essentially green. Pocock

said her students called it “green red lettuce.” It had the lowest level of

anthocyanin pigment concentration, which has antioxidant properties along

with providing the attractive red color. The lettuce grown under CWF light

A comparison of HPS and LED lighting in a greenhouse at Colorado State University.

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had the highest concentration of anthocyanin, although the other LED lighting

performed reasonably well also. We didn’t know it at the time, but we would

learn more about Pocock’s Rouxai research later in 2017 and we published a

news article on that work.

Unfortunately, there is no one spectral recipe that is beneficial for all plants, and

Pocock made that clear on her next slide. A red butter lettuce Pocock tested did

not respond well to CWF and did much better under PC LED, although the red

coloration was missing with that cultivar and also with another called Salanova

that is in the red oakleaf family to which Rouxai also belongs. Referring to the PC

LED lighting, Pocock said, “Under this there is no photochemistry going on with

respect to secondary metabolites.”

CLOSING THE LOOP ON HORTICULTURAL LIGHTING

“The future is knowledge-based controlled environment agriculture,

understanding these metabolic pathways,” said Pocock. Rather than just

experimenting with different light recipes, Pocock said we need to “get inside the

plant cell and go from there with the lighting.” She said for the past seven years,

she has been working on remote detection of plant health through reflection of

light from plant leaves along with chlorophyll fluorescence emitted from foliage.

In her LESA lab, Pocock has been working to develop a low-cost reliable sensor that

can be used in a grow facility. She said that “the chlorophyll molecule intrinsically

fluoresces.” She added that this known property has been used since the 1950s

by plant physiologists to determine if a plant is stressed. Pocock has what she

described as a very-expensive Heinz Walz pulse amplitude modulation (PAM)

fluorometer in her lab that allows her and her students to see how every photon

is being used on a research basis. She showed images from a stress test done on

basil where temperature was lowered. The results can be expressed as the effective

quantum yield or the probability that a photon will be utilized by the plant.

Of course, such a PAM fluorometer isn’t usable on a scalable basis in a production

grow facility. So Pocock and students have been pursuing a sensor design, albeit

in a project that is not presently funded. The second-generation prototype used

an LED emitting at 470 nm and a nearby photodetector, both located 40 cm above


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a plant with a field of view diameter of about 5 in. The prototype proved accurate

at detecting stress in basil.

The project has since moved to a third-generation prototype that is housed in a

more reliable and robust growing chamber with a larger field of view, which feeds

data continuously to a computer. The system can accurately detect day and night,

when a plant is undergoing photosynthesis, and conditions such as drought,

simply by monitoring the response from the plant.

“Our future is self-regulating light control,” said Pocock. She acknowledged

that there is much research to be done. But she asked, “Why should I impose a

spectrum on a plant when it can tell me how it is doing?” She believes that we

will ultimately “use the physiological state of the plant to control the light.”

Of course, such a future would be good for the world of LEDs and SSL. LEDs with

tunable spectrum would still be a perfect match for such a closed-loop system.

The attendees at the conference may not have expected to learn such a lesson

about the future, but their positive reaction to the Closing Plenary made it clear

that they greatly valued the insight as well as the rest of the knowledge imparted

by a stellar lineup of informed speakers. Stay tuned for more details and updates

on our Europe and US conferences for 2018 (horticulturelightingconference.com).


http://horticulturelightingconference.com/


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* This article was published in the April 2017 issue of LEDs Magazine.

Understand energy efficiency of LED horticultural lighting systems

The true efficacy of LED fixtures for horticultural lighting depends on many factors, explains JOSH GEROVAC, and lighting manufacturers and growers need to take a broad view to ensure optimal yields and energy efficiency.

THERE ARE MULTIPLE considerations that a business faces when

evaluating light sources to use for horticultural lighting, including

but not limited to: light intensity, spectrum, uniformity of light

distribution, energy efficiency, and fixture lifespan. Horticultural

lighting systems convert electrical energy into light that plants use to drive

photosynthesis for growth and development, and LED-based sources can offer a

spectrum tuned for the application. Still, ascertaining the efficiency or efficacy

of such solid-state lighting (SSL) systems is a challenge. There are several factors

that impact the overall efficiency of a lighting system, relative to the specific

application at hand. This article will discuss how the design of a lighting fixture

FIG. 1. The ability to deploy lighting solutions within inches of a crop canopy is a breakthrough for vertical farming applications. Properly designed LED solutions enable higher yields per square foot compared to poorly designed LED solutions and other lighting technologies such as HPS and fluorescent.



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influences energy efficiency and how in turn this reality can influence the overall

profitability of a controlled-environment plant growth facility.

Indeed, the efficacy with which a horticultural light fixture converts electrical

energy into usable light for plant growth is critical to the success of any controlled

environment plant growth facility - often called CEA (controlled environment

agriculture). Fig. 1 shows a vertical farm that is one example of CEA. Realize that

the efficacy consideration

is necessarily far different

for lighting tuned for plants

compared to lighting tuned

for humans.

Metrics for horticulture

We will start by defining

the proper metrics used

for horticultural lighting

applications to add context

for the rest of the article.

Plants primarily use

wavelengths of light within

the visible range of 400-

700 nm to drive photosynthesis (Fig. 2), which is why this range is also called

photosynthetically active radiation (PAR). Photosynthetic photon flux (PPF)

measures the total amount of PAR that is produced by a lighting system each

second. This measurement is taken using a specialized instrument called an

integrating sphere that captures and measures essentially all photons emitted by

a lighting system. The unit used to express PPF is micromoles per second (μmol/s).

Photosynthetic photon flux density (PPFD) measures the amount of PAR that arrives

at the plant canopy. PPFD is a spot measurement of a specific location on your plant

canopy, and it is measured in micromoles per square meter per second (μmol/m2/s).

Last, we will discuss photon efficacy, which refers to how efficient a horticultural

lighting system is at converting electrical energy into photons of PAR. If the PPF of

the light is known along with the input wattage, you can easily calculate photon

FIG. 2. The graph depicts the average plant response to photosynthetically active radiation (PAR).



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efficacy for a horticultural lighting system. Given the unit for PPF is μmol/s, and

the unit to measure watts is joules per second (J/s), the seconds in the numerator

and denominator cancel out, and the resulting unit becomes μmol/J, which is the

unit of measure used to represent efficacy. The higher this number is, the more

efficient a lighting system is at converting electrical energy into photons of PAR.

Common approaches to horticultural lighting

Now that we have covered the proper metrics to characterize horticultural

systems, we can dive into the nuances of fixture design and what makes

a horticultural lighting system energy efficient. The most commonly used

horticultural lighting systems worldwide are based on high-intensity discharge

(HID) lighting and mainly high-pressure sodium (HPS) lamps. HPS fixtures were

not designed specifically to grow plants. They were designed to light roadways

and parking garages. Ready availability and high output levels, however, led to

deployment in horticulture and subsequently their popularity in the application

can be attributed to the fact that they deliver very high light intensities and most

of the light emitted is in the 565-700-nm range - effective wavebands that can

drive photosynthesis.

One drawback to using HPS fixtures for horticultural lighting is the large amount

of radiant heat that is produced. The surface temperature of HPS bulbs can reach

temperatures above 800°F, which necessitates adequate distances between the

plant canopy and the fixture to avoid damage to plant tissues. The inverse square

law comes into play as you increase the mounting height of a fixture, which can

reduce the coefficient of utilization (CU), a term used by lighting professionals

to describe how effective a luminaire is at delivering light to a target plane. The

energy efficacy of HPS fixtures has increased over the years and with the advent

of double-ended HPS fixtures that are now capable of achieving photon efficacies

of 1.7 μmol/J.

Moving toward LEDs

Let’s consider the chronology of the application leading to LED use in horticultural

lighting. In 2014 the most efficient LED-based horticultural lighting systems were

as efficient as double-ended HPS fixtures. The long lifespan (L70 ≥50,000 hours)

compared to that of an HPS bulb intrigued several growers to switch to LEDs.

However, the relatively high cost of LED-based horticultural lighting systems


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compared to HPS fixtures limited the transition

to SSL despite comparable efficacy.

LED chip manufacturers have improved the

efficacy of components available to horticultural

lighting manufacturers over the last several

years, which has enabled them to significantly

improve photon efficacies that now surpass HPS

fixtures, and they continue to improve every

year. Indeed, LED-based horticultural lighting

systems are now capable of achieving photon efficacies 45% greater than double-

ended HPS fixtures. While the improved efficacy of individual components has

improved the efficiency of LED-based horticultural lighting, it is also just one

variable responsible for the improvement over HPS technology.

LED system thermals

There is a common misconception surrounding LED lighting when it comes

to heat produced by the fixture. Many growers believe that LEDs produce less

FIG. 3. Harsh and dirty environments such as those in greenhouses can quickly cause active cooling systems to fail, and in turn, cause the entire lighting system to fail. In addition to improved energy efficiency, passive cooling systems do not require moving components prone to breaking and clogging.



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heat than HPS fixtures, which is only true if the LED fixture is driven at a lower

wattage. If you have a 600W LED fixture and a 600W double-ended HPS, they will

produce heat in the same general range from a magnitude perspective.

The major difference between LED and HPS systems is how much PAR energy is

produced from those 600W (goes back to efficacy), and how the heat is radiated

from the fixture. Most heat from HPS lamps is radiated down towards the crop

canopy, whereas LEDs produce most of their heat at the connection site of the

component where it is assembled to a printed circuit board (PCB). And the heat

is typically conducted to the PCB and maybe a heat sink, and removed via

upward convection.

So the proximity at which a fixture can be placed near plants without damaging

tissue from radiant heat is one of the major benefits of LEDs as a source for

horticultural lighting systems. However, if this heat is not removed effectively

from the PCB with an appropriate thermal management system, the longevity of

the LED components will decrease significantly.

There are two ways to cool lighting systems in commercial horticultural

environments that will impact the photon efficacy of the fixture. Passively

cooled fixtures utilize heat sinks to dissipate heat from the circuit board, while

actively cooled fixtures rely on fans or water to dissipate heat. Fans that are used

to cool fixtures consume energy and will decrease the overall photon efficacy

of a fixture. Additionally, if a fan fails during the operation of the fixture, the

LEDs on the PCB are likely to overheat and burn out. Even if they don’t fail

catastrophically, reduced power output will dramatically reduce the usable life

of the LED fixture. This is a very important feature that growers need to consider

when comparing horticultural lighting systems.

Spectrum and efficacy

Another important feature that will influence the photon efficacy of a

horticultural lighting system is the spectrum of light emitted. The most efficient

wavelengths that are used for horticultural lighting systems are red (660 nm)

and blue (450 nm). Traditional LED-based horticultural lighting technology uses

mainly red LEDs with smaller proportions of blue to achieve the highest photon

efficacy possible.



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While red LEDs have the highest photon efficacy,

plants did not evolve in nature under narrowband

wavelengths. So red LEDs alone don’t produce the

most efficient spectra with regard to optimizing plant

growth and development. This is especially true in

situations where lighting systems are used for sole-

source lighting as in vertical farms, as compared to

supplemental greenhouse lighting (Fig. 3).

Several horticultural lighting manufacturers

market their products’ “special spectrum” based

on the absorption peaks of chlorophyll a and b;

however, they fail to mention that those chlorophyll pigments are extracted

from plant leaves and measured in vitro. The action spectra of light quality on

photosynthesis (Fig. 2) was created from research that was conducted in the 1970s

by Drs. McCree and Inada, which showed while there is a correlation between

photosynthesis rates and the action spectra of chlorophyll a and b, they are not

FIG. 4. The spectrum (i.e., color) of light emitted from a horticultural lighting solution has a significant impact on both energy efficiency and overall plant growth and development. While red and blue light is more energy efficient to produce, a broad spectrum achieved with a light engine such as the one pictured will target more photoreceptors for improved cultivation.



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the only wavelengths responsible for photosynthesis. Prior to this research, it was

a common misconception that since chlorophyll absorbs light mainly in the red

and blue portions of the visible light spectrum (leading to the green color of plant

leaves), green light was not used by plants for photosynthesis.

The work conducted by Drs. McCree and Inada was fundamental in understanding

the influence of spectral light quality on photosynthesis; however, they developed

their action spectra based on single leaf measurements of photosynthesis at low

light intensities. Over the past 30 years, several studies conducted on whole plant

photosynthesis with higher light intensities indicate that spectral light quality has a

much smaller effect on growth rate than light intensity.

Spectral light quality does strongly influence plant developmental responses,

such as: seed germination, stem elongation, and flowering; along with secondary

metabolites and flavonoids, which influence the taste, look, and smell of plants.

Therefore, LED manufacturers need to find a balance between using the

most electrically-efficient LEDs and ones that elicit optimal plant growth and

development habits that growers desire. The exciting thing about LED technology

for horticultural lighting is that researchers finally have the tools available to

stand on the shoulders of Drs. McCree and Inada and explore photobiology even

further, developing light recipes for optimal growing.

Form factor and beam control

The last topic we will cover has to do with the form factor of a fixture, beam

optics, and light intensity. When you are thinking about the overall efficiency of

a horticultural lighting system, PPFD and CU need to be considered. But while

photon efficacy of the fixture itself is very important for horticultural lighting, if

the light being produced in an actual application is not landing on a crop evenly

and efficiently, the true energy efficiency of that solution is greatly reduced.

HPS fixtures rely on reflectors to spread light evenly over a crop canopy since

there is only a single light source (360° light bulb) per fixture. Another advantage

LEDs have over HPS is the ability to have hundreds of light sources spread across

a fixture with custom beam optics that can create very uniform light patterns

without the use of reflectors. Fig. 4 depicts a typical LED light engine.



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When designed appropriately, this flexibility in form allows solutions with

very high CUs where the majority of the light generated is landing on the plant

canopy and not wasted on aisles or walls in controlled-environment plant growth

facilities. After all, any light generated that doesn’t reach a crop canopy is wasted

energy (and money). This is critical for growers to consider when choosing a

horticultural lighting system.

Takeaways

Not all LED lighting systems are created equally, so it is important for growers

to get lighting designs from manufacturers that show average PPFD at defined

mounting heights and the light distribution pattern for their plant growth facility.

The form factor and light distribution of a horticultural lighting system will

influence the number of fixtures needed in a facility, which is another factor that

will impact the overall energy efficiency of a plant growth facility.

The take-home message is that the energy efficiency of horticultural lighting

systems is based on several factors, not just one. Using the correct metrics and

understanding the factors that influence the energy efficiency of a horticultural

lighting system will influence the overall profitability of a controlled-environment

plant growth facility.

For more information on this topic, please see “How to compare grow lights” at

http://bit.ly/2lkXDGD.

JOSH GEROVAC is a horticulture scientist at Fluence Bioengineering (https://

fluence.science/) and has spent the last decade working in controlled environment

agriculture, ranging from growth chambers to commercial greenhouses. He has

a Bachelor of Science in Horticulture Production and Marketing, and a Master of

Science in Horticulture, both from Purdue University.



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* This article was published in the June 2017 issue of LEDs Magazine.

Buyers benefit from LED grow light guidance

With LED-based horticultural lighting on the rise, specifiers and end users need education to select the optimal fixtures for projects. RYAN MITCHELL and CHARLIE SZORADI deliver a guide to navigating spec sheets and performance calculations for best results.

THE EARTH’S POPULATION is projected to reach 10 billion by 2050, and

there are growing concerns about water, energy, and food availability

for such a high number of people. To maintain our current water

supply and produce enough food to feed our fellow human residents,

several different practices must

be adopted within the agricultural

sector. One potential solution to

the problem is growing vegetables

in water through hydroponics,

aquaponics, or aeroponics. LED-based

horticultural lighting works as an

excellent companion technology to

enhance crop production for indoor

applications, especially in warehouses

- in what is known as vertical or

urban farming - versus greenhouses.

The three water systems are soil-

less methods of agriculture that

can produce 5× the amount of food

in the same space as typical outdoor agricultural methods. Furthermore, these

practices utilize at least 90% less water than the irrigation practices used in

FIG. 1. Sample linear LED grow light modules with different color diodes on each module.



22


outdoor agriculture. With food and water availability possibly being the greatest

future challenge facing humankind, these systems will provide significant relief

to those concerns.

One common question with such agricultural systems is how the yields compare

to soil-grown harvests. As stated earlier, these systems provide the ability to

grow roughly 5× the amount of food in the same space compared to outdoor

agriculture. The ability to stack the water and lighting systems in shelves allows

for a condensed and efficient use of space. Along with that, utilizing LED grow

lights designed to deliver appropriate light spectra for each crop, provides more

photosynthetic active radiation (PAR) than what most plants receive from the

sun (Fig. 1). For instance, Mount Vernon, which is one of the most notable farm

towns in Iowa, receives a maximum of about 14 hours of photosynthetic light a

day in the summer, but in the winter it can drop to as low as eight hours of light.

When equipped with horticultural solid-state lighting (SSL), plants reach their

maximum photosynthetic potential every day. Growers just need to be careful

about giving their crop too much of the heat energy that comes with the any light

source. Therefore, periods of no light exposure must be set aside each day for

plants. The reduced heat and the lower electricity operating costs of LEDs have

opened a whole new chapter in agriculture.

Reaping the economic benefits

With greater yields than the common outdoor methods of agriculture, the next

concern is whether these horticultural systems are economically efficient. The

quick answer is “yes” - with an asterisk - based on three key factors: type of plant;

sales region; and cost of electricity

People outside of the agriculture industry might assume that cannabis, with

medical and recreational marijuana, is the only “cash crop.” Since cannabis takes

multiple months to grow and grows multiple feet tall prior to harvest, it uses up

more real estate - horizontally and vertically - than other crops like lettuce and

micro-greens. Indoor farmers can “rack and stack” leafy greens four or five high

and turn the crops more than once a month. California lettuce is shipped all over

the US, and the cost at wholesale is often about $1.50 per head of romaine. The

trans-continental cost of each head of lettuce with diesel fuel is about $0.30, while



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horticultural SSL can grow the same head of lettuce for less than $0.15. Fresh,

local, and organic vegetables are now more affordable than ever with LEDs.

For building illumination, LED manufacturers and solution providers often look

to retrofit existing buildings in regions that have higher-than-average electricity

costs. The savings payback comes faster with higher cost/kWh. For indoor

farming, the opposite is true, because the lower the cost/kWh the lower the

FIG. 2. Sample wavelength for an LED-based horticultural fixture engineered to grow flowering plants from tomatoes to licensed medical marijuana.



24


cost of goods sold for each plant in the harvest. Given that off-peak electricity

(typically late night to early morning) is in less demand and lower cost than

peak power (during the day and evening), next-generation indoor farmers will

be able to power their LEDs using off-peak electricity and supplement as needed

with skylights and clearstory natural light during the day. Using remnant

warehouses with LEDs and any of the water-saving systems is a cost-effective

way to overcome the challenges of the water, energy, and food security nexus.

A guide to buying grow lights

Finding the right grow light for your horticulture project can be a difficult and

daunting task. Units of measurement such as wattage, wavelength, lumens,

PAR, micromoles (μmol), and photosynthetic photon flux density (PPFD)

commonly lead to misconceptions over the quality and efficiency of a grow

light. So how can a buyer select the right grow light to fulfill their needs?

This buyers guide includes two key parts: navigating specification sheets and

performance calculations.

Navigating specification sheets. First, let’s look at what is not important. Lumens

are a common unit of measurement in lighting spec sheets. The issue with

lumens is that they are measure of responsivity by the human eye to various

energy wavelengths (visible light output). If a lighting company’s representatives

are promoting lumens for its grow lights, then they are unqualified and a waste of

the buyer’s precious time.

Understanding the correct color of the lighting is a crucial aspect for any

horticulture venture. Whether you are looking for full spectrum, a wavelength

combination, or a specific wavelength, having the right color is essential for

optimal growth in plants. You should ask a lighting expert at the company

from which you may purchase the products, or do some scholarly research on

what wavelengths are best for certain plants. This will assist in high yields and

optimal growth.

Comparing wattage is another way many users decide on horticultural lighting.

The issue with looking at just the wattage is that radiometric lighting efficiency

can vary greatly through different brands of products. Some companies’ grow

lights may be higher in wattage than others, however, the efficiency may be



25


STEM factors into leading-edge agriculture

The educational benefits when using advanced agriculture systems with grow

lights are immense. Science, technology, engineering, and math (STEM) is

a focus point of many K-12 schools and universities in the US and beyond.

Hydroponics, along with other systems like it, incorporates all aspects of

STEM, which makes it a highly

effective tool to utilize in schools.

With the lighting, students

can learn about how different

wavelengths are optimal for

photosynthesis for different plants.

They can also build their own

systems from scratch, which forces

them to understand how the water

will flow, maintaining pH and

water temperature, and monitoring

the electrical conductivity (EC)

rating which reveals how much

fertilizer salts are in the water.

These experiments will be

highly engaging for students and

provide an excellent way to better

understand the science behind

these agricultural systems.

Another major benefit for

utilizing hydroponic, aquaponic,

and aeroponic systems in

combination with horticultural lighting in school is the potential nutritional

value - especially in inner-city schools. In many cultures, children are

becoming more susceptible to becoming overweight and obese, and it is

crucial for students to have better nutritional options available. By having

an agricultural system placed in a school, fresh vegetables can be readily

available to students. Furthermore, the vegetables being consumed would

come directly from the hands of the students. This will make it much more

Produce grown in-house at educational facilities using indoor agricultural systems that leverage LED horticultural lighting could deliver both a learning opportunity and improved nutrition on campus for students.



26


likely for adolescents to include vegetables in their daily diets since they could

be working directly with them in a consistent manner. The combination of

better nutrition and a more engaged science curriculum is an example of why

these systems need to be put to use in schools.

With so many benefits to fully-integrated horticultural systems, the tipping

point for next-generation agriculture may arrive sooner than many expect.

The lighting is one of the major equipment costs. Buyers often look at price and

wattage as their gauge for effectiveness. The guidelines explained in the article

may help steer testing and purchase decisions.

weaker in comparison to the output of photosynthetic light. Therefore, a fixture

with a higher wattage does not necessarily mean it is more powerful and

beneficial when used for horticulture applications.

Let’s explore the indicators of performance and efficiency relative to micromoles,

PPFD, and PAR.

Micromoles indicate how many photons of lights are emitted. PPFD is the

number of micromoles emitted in a certain area per second. PAR is the amount

of photosynthetic light emitted in the visible range of 400-700 nm; this drives

photosynthesis. Now these all sound like equally great metrics to consider when

searching for a grow light; however, PPFD includes both photosynthetic light and

area. This makes it a very efficient comparison tool when looking at different

horticultural lighting products.

One aspect to note with PPFD is the area used in the measurement. Look for a

peak PPFD number (PPFD = μmol/m2/s) and an average PPFD. These metrics will

reveal how much photosynthetic light is emitted directly under the grow light

along with the surrounding area. This is because some lights have an extremely

high PAR rating directly under the light but a drastic decrease in PAR in the

surrounding area. So it is crucial to determine the PPFD average for the area in

which you are hoping to grow plants for each individual grow light (PPFD = PAR/

m2). Even distribution of PPFD will help create more even growth of the plants.





27


Performance calculations. To compare the cost and performance of two or more

grow lights, follow these steps to make sure the comparison is apples to apples.

Step 1: Ask your contact at the lighting manufacturer, supplier, or the

representatives to provide information on their technology based on meeting

the specific needs of a given scenario, such as the one in the table, given sample

specs for comparing fixtures.

Step 2: Do the quick math. First, divide the cost of the solution by the square

footage of the solution coverage area at the average PPFD level to get grow light

equipment cost/ft2. Next, divide the wattage of the solution by the square footage

of the solution coverage area to get W/ft2. Finally, compare the technology - the

lowest cost and W/ft2 are the winners.

Following is a frame of reference on cost based on an example from Independence

LED Lighting (Fig. 2) with similar specs as in the table. The LED grow light GS1250

is a 4×8-ft linear module rack system with a coverage area of 60 ft (6×10 ft) and

1250W power consumption. Note that this system is designed to replace two

1000W metal-halide (MH) fixtures or four 400W fixtures that typically have a

ballast factor greater than 450W each. To meet the needs of the targeted 240 ft2,

the grow light system would need four racks. The cost per rack will vary based on

wavelength/diode selection but is often between $1750 and $2500.

For this exercise, four racks at $2000 each adds up to $8000. The wattage of

1250W per rack × 4 = 5000W for the horticultural lighting solution area. So

then calculate the racks as $8000/240 ft2 = $33.33 per ft2 for the LED grow light

equipment. And electricity consumption would be calculated as 5000W/240 ft2 =

20.8W/ft2.

In comparison, the cost and power consumption of an MH horticultural lighting

system for the same area would be calculated as follows. Four MH fixtures at

450W each × 4 (racks) = 16 fixtures using 7200W. The cost of $185 per fixture

× 16 fixtures = $2960 total for the equipment. Take the total of $2960/240 ft2 =

$12.33 per ft2 for the comparable MH grow light equipment. Finally, the electricity

consumption can be determined as 30W/ft2 (by calculating 7200W/240 ft2).



28


The LEDs are more expensive upfront but more efficient with 30% lower ongoing

operating costs. Now, we want to answer the question “How much savings comes

with the more efficient lights?”

We need to set two key variables that you can adjust accordingly. For the purpose

of this calculation, we will use daily hours of illumination - 16 hr (5840 hr/year),

and cost/kWh - $0.12 (US average).

Key square footage data points are:

:: Ongoing energy (30W for LED - 20.8W for MH) = 9.2W saved/ft2

:: The upfront cost difference ($33.33 LED - $12.33 MH) = $11 saved/ft2

The related formulas are:

:: Watts saved/1000 × Annual hours = Annual kWh savings/ft2

:: Annual kWh saved × Cost/kWh = Annual cost savings/ft2

:: Added upfront cost/Added annual cost savings gives the payback time

So, for example, the calculations would result in:

:: 9.2W saved /1000 × 5840 hr = 53.7 Annual kWh savings/ft2

:: 53.7 Annual kWh saved × $0.12 = $6.44 Annual cost savings/ft2

:: $11 Added upfront cost/$6.44 Added annual cost savings = Payback time is 1.7

years

Over the long 100,000-hour life of many LEDs, the payback in just over a year

and a half presents a favorable business advantage. For a facility with 24,000 ft2

of grow area, the annual savings of $6.44 adds up to $154,000 per year and more

than $1.5 million over 10 years. An increasing number of LED manufacturers and

value added resellers (VARs) offer $0 upfront cost financing options. So in your

review of product options, make sure to ask about flex payment and financing

plans; then the monthly energy savings can pick up the cost of the LEDs rather

than your working capital upfront.



29


Step 3: Order samples of the two or three horticultural lighting solutions that

are mathematical winners with the lowest equipment cost/ft2 and the lowest

W/ft2. Ask the manufacturer to refund the cost of the samples if you return the

technology within 90 days.

Step 4: Request refinements to the wavelengths if necessary and review monthly

financing options for all or partial payment of the equipment.

Step 5: Place a purchase order with the company that delivers on the

mathematical promise and on the in-field performance to meet the needs of your

plants and your business.

Conclusion

As we have explored, not all LED horticultural lighting is created equal. Let’s

recap the main points when selecting LED grow lights. Ask manufacturers for



30


photometric layouts to see the PPFD at target elevation levels, and look for the

most even PPFD distribution over hot spots. Line up fixture comparisons based on

apples to apples solutions that cover the same area at the same wavelength and

PPFD levels. You can even out the fixture variables by breaking the performance

down to the square foot. Use the equipment cost per square foot and the electricity

operating cost per square foot to guide your decisions. Test samples before making

a large purchase, and ask the manufacturer in advance to agree to refund the cost

of samples that you don’t keep. Last, financing will allow the monthly savings to

help pay for the lights and maximize your return on investment.

RYAN MITCHELL is account manager and CHARLIE SZORADI is chairman and

CEO at Independence LED Lighting (independenceled.com).


http://independenceled.com/

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Phone: 847-932-3662

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Lake Forest, IL 60045

Phone: 847-367-4378

Homepage: https://www.aptsources.com/

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