KEY ASPECTS ABOUT THE USE AND MANAGEMENT OF

LED LIGHTING IN CROP PRODUCTION

OUTLINE
- Response to light quality
- Response to light quantity
- Light requirements (Light quality/ light quantity) for
most common crops
• Leafy greens
• Vine crops
• Cannabis
• Strawberry
• Ornamentals: Orchids
- How to select the best fixture?
- Lighting options for indoor farming
- Lighting option for supplemental lighting applications
- Questions to ask when selecting a light manufacturer
- How to request a light plan

As LED grow lights continue to become more affordable, an increasing number of greenhouse growers
and vertical farmers are considering whether the lights would benefit their production systems. Several
studies and growers applications have demonstrated the development of new lighting technologies
such as light-emitting diodes (LEDs) can increase the capability to provide ideal light conditions to
crops, making possible the improvement of crop performance and product quality.

In order to understand how light can improve production, we need to learn how plants respond to
light, which options of lighting are available, how to select the best technology, and apply the best light
management.

RESPONSE TO LIGHT QUALITY

Light quality refers to the specific light spectrum received by plants. Light itself can occupy a large
fraction of the electromagnetic spectrum. But just a fraction of the spectrum is utilized by plants to
make photosynthesis. This section of the light spectrum from 400 nm to 700 nm is called Photosynthetic
Active Radiation (PAR) and can be measured in μmol m-2 s-1 (Photosynthetic Photon Flux Density,
PPFD). PAR will provide us the number of light particles that plants are receiving per area in a fraction
of one second within the photosynthetic active spectrum of light. The process of photosynthesis starts
with the absorption of light with the help of a molecule called chlorophyll. Chlorophyll has peaks of
absorption on specific wavelengths: From 640 to 680 nm where we find the red color of light and 430

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to 450 nm where we can find blue light.

The development of new lighting technologies such as light-emitting diodes (LEDs), increases our
capability to provide ideal light conditions to our crops, making it possible to improve crop performance
and product quality.

Each crop has a particular response to light quality. By providing a particular light spectrum to plants, plant
growth, development, and photomorphogenesis reactions can be controlled. Photomorphogenesis is a
process by which plants produce phytochemicals in response to light signals. Phytochemicals present
in vegetables have an impact on people’s health. The biosynthesis, metabolism, and accumulation of
phytochemicals can depend on light quality. This means providing a specific light spectrum to plants can
control plant shape, growth and also have an impact on taste, aroma, chemical compounds, nutrition
quality, etc.

RESPONSE TO LIGHT QUANTITY

All crops have specific light requirements. By knowing minimum and optimum levels of light for our crop
we can manage our environment to improve crop performance. When the ambient light exposure is
below the minimum requirements we need to apply supplemental lighting in order to maintain our crop
production at a healthy and consistent pace.

On the other hand, when our ambient light levels are optimal we can regulate the light to influence other
aspects of our environment such as air temperature and humidity by applying specific products to
reduce heat exposure in our greenhouse.

Light management will always be a key factor in our crop performance. But, how can you be sure that
your plants are receiving enough light? There is a way to measure the light intensity received by your
plants.

Light occupies a large portion of the electromagnetic spectrum. But just a fraction of the spectrum is
utilized by plants for photosynthesis. The wavelengths of the light spectrum from 400 nm to 700 nm are

3
called photosynthetically active radiation (PAR). PAR can be measured in μmol m-2 s-1 and is referred
to as photosynthetic photon flux density (PPFD). PAR provides the number of light photons that plants
receive per area in a fraction of one second. This measurement can be monitored by a photosynthetically
active radiation sensor.

Daily light integral (DLI) is used to understand and evaluate the quantity of light plants are receiving. DLI
is a cumulative version of PAR that measures the quantity of light received by plants per area per day
(mol m-2 d-1).

Many studies have been done evaluating crop performance under different DLI levels. This information
allows growers to determine if light levels in their greenhouses or indoor farms are high enough to ensure
good crop production. DLI is calculated using PPFD and photoperiod (hours of light) in the formula:

DLI= (PPFD) (Photoperiod) (3600)

1,000,000

LIGHT REQUIREMENTS FOR MOST COMMON CROPS

LEAFY GREENS

Production of leafy greens inside greenhouses and plant factory systems are great options to produce
high marketable products distinguished by uniform and consistent quality.

Leafy greens including lettuce, herbs, and microgreens are products where customers look for: color,
texture, taste, shelf life, variety, and even they compare nutritional content. The increasing demand
for quality for leafy greens creates a real competitive advantage for growers using hydroponic indoor
systems.

Lettuce and herbs are crops that can be grown in both greenhouse and indoor vertical farming. Artificial
lighting can be implemented in any of these two food production systems in order to improve quality and
yield in leafy greens production. But in order to get expected results, we must learn to manage lighting.

LETTUCE
DLI - Minimum 10 mol/ m2/ day, Optimum 20 mol/ m2/ day

Lettuce is a crop that can be grown either in greenhouses or vertical indoor farming systems. Light
Specifications for these growing systems have some variations. Recommendations for indoor vertical
farming systems include the use of artificial lighting creating an ambient of light with a maximum DLI
of 17 mol/ m2/ day. Based on research conducted by Cornell University an exposure of more than
three days to a DLI of 17 mol/ m2/ day in lettuce can trigger morphological problems such as tip burn.
Ambients inside plant factories are very different from a greenhouse, usually, the volume of air and its

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friction over the plant canopy facilitates the development of the “boundary layer”: A layer of heavy air
sitting over the stomata which can reduce gas exchange and uptake of water and nutrients. On the
other hand greenhouse, lettuce production can tolerate more light without showing any physiological
problems. When spotting tip burn inside of greenhouses the main source of the issue most of the time
is lack of proper air ventilation.

BASIL

DLI - Minimum 10 mol/ m2/ day, Optimum 20 mol/ m2/ day

Basil is by far the most popular herb on the market. There are a lot of different recommendations for
optimal basil growing conditions. In general in comparison to other leafy greens such as lettuce Basil can
tolerate higher ranges in some environmental variables like light, humidity, temperature, and nutrients.
Basil can grow under low light intensities (12 mol/ m2/ d), but it thrives under high intensity (17+ mol/
m2/ d). The lighting quality (spectrum) selection depends on how the crop is sold. Plants that are sold as
a living plant in a sleeve may need to reach a minimum height before they are sellable, for this situation
growers might want a light with a heavy red spectrum and maybe even some far-red to encourage stem
elongation. Growers will then plant at a high density to get a good thick canopy of basil in the sleeve. If
growers are selling cut basil in a clamshell, or maybe just basil leaves with no stem, they might prefer
to have a compact plant with thicker leaves so the weight is focused on the leaves. These growers may
want a spectrum with more blue to encourage compact growth and thicker leaves.

MICROGREENS

DLI - Minimum 10 mol/ m2/ day, Optimum 12 mol/ m2/ day

Microgreens are the seedlings of vegetables and herbs harvested just after the cotyledon leaves have
developed. Several studies have demonstrated the use of blue and red light for growing microgreens
significantly improves quality: Including speed of growth, color, texture, nutrition quality.

Recommended DLI for the common leafy green crop is as follows:

Indoors DLI Greenhouse DLI

Microgreens 6 mol/m /d
2
10- 20 mol/m2/d
Lettuce 12-17 mol/m2/d 10- 20 mol/m2/d
Basil 12-17 mol/m /d
2
10- 20 mol/m2/d

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LEAFY GREENS RESPONSE TO LIGHT QUALITY
LIGHT QUALITY PLANT RESPONSE
FAR- RED Increase total biomass and leaf elongation (Stutte et al., 2009)
(700- 750 nm) Decrease anthocyanin concentration (Stutte et al., 2009; Li and Kubota, 2009)
Pre-harvest exposure reduces nitrate concentration (Wanlai et al., 2013; Ohasi-Kaneko et al.,
2007; Samouliene et al., 2009; Samouliene et al., 2011)
RED LIGHT
Increase phenolic (Li and Kubota, 2009; Zakauskas et al., 2011) and carotenoid (Brazaityte et al.,
(640 - 680 nm) 2014) concentration.
Stimulates leaf and stem elongation
High light intensity promotes growth compared to fluorescent lamps (Johkan et al., 2012),
GREEN LIGHT reduces nitrate concentration, and increases ascorbic, tocopherol, and anthocyanin content
(500 - 550 nm) (Samuoliene et al., 2012).
Can penetrate canopy and leaf tissue to promote photosynthesis
Increase ascorbic acid (Ohashi-Kaneko et al., 2007), B- carotene (Lefsrud et al., 2008),
anthocyanin (Ohashi-Kaneko et al., 2007) content and root growth (Johkan et al., 2010).
BLUE LIGHT
Decrease nitrate concentration (Ohashi-Kaneko et al., 2007)
(430- 450 nm)
Promotes compact growth
Increase anthocyanin concentration. Important for red/purple leafy greens coloration
UV-LIGHT Increase anthocyanin concentration (Li and Kubota, 2009). Important for red/purple leafy
(10 - 400 nm) greens coloration

*Much of this research was conducted in germination or growth chambers. Greenhouse growers should
consider this data useful but remember that the selection of glazings, shade materials, and age of
greenhouse will have equal if not more significant impacts on light than their supplemental light sources.

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VINE CROPS

TOMATO- DLI - Minimum 20 mol/ m2/ day, Optimum 30 mol/ m2/ day

PEPPER- DLI - Minimum 10 mol/ m2/ day, Optimum 30 mol/ m2/ day

CUCUMBER- DLI - Minimum 15 mol/ m2/ day, Optimum 30 mol/ m2/ day

Greenhouse production of hydroponic tomatoes is increasing worldwide every year. The reason? All
the advantages provided by these growing systems! The principal advantages of hydroponic controlled
environment agriculture (CEA) include high-density maximum crop yield, year-round production, more
efficient use of water and fertilizers, consistent crop quality, minimal use of the land area, and suitability
for mechanization, disease, and pest control. The major advantage of hydroponic (CEA) compared to
field-grown produce is the isolation of the crop from the soil, which often has problems of diseases,
pests, salinity, poor structure, and/or drainage. Research has demonstrated tomato yield can be
significantly increased when implementing hydroponic greenhouse production. This is the reason why
every year we have more growers making large investments in hydroponic greenhouses systems for
tomato production.

Technology is improving and its application in greenhouses systems can help to maximize benefits in
hydroponic controlled environment agriculture. But how can we decide where to invest when managing
a hydroponic tomato greenhouse? This article has the purpose to guide you on the key aspects to
improve management in hydroponic tomato production. By understanding, crop management and
operational needs growers can take better decisions to run a greenhouse more efficiently and with
better results.

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ADVANTAGES OF SUPPLEMENTAL LIGHTING IN VINE CROPS
Sunlight is the main source of light when growing tomatoes inside greenhouses. Natural light can vary
widely depending on greenhouse structure, location, and time of the year, providing sometimes lower
light levels than required by a tomato plant. Supplemental lighting can help to improve light levels inside
the greenhouse system and also can be used to regulate stem elongation and flower development.

VINE CROP RESPONSE TO LIGHT QUALITY

There is now plenty of research demonstrating the benefits of applying specific light quality to tomato
plants. The table below shows some results on how different “colors” of light can affect tomato
development and quality.

LIGHT QUALITY IN VINE CROPS

TOMATO

Light quality Plant response

By lowering R:FR ratio, tomato seedling stem elongation was significantly increased (Chia and
Far-Red LIGHT
Kubota, 2010).
The use of supplemental red light increased tomato fruit yield by 14 percent (Lu et al., 2012) and
Red light
chlorophyll content compared to the control treatments (Yang et al., 2018).
Partial replacement of blue and red light with green light increased growth of plants in dense
Green light
canopies improving yield, chlorophyll, and carotenoid concentration (Kaiser et al., 2019).
Proved to be required for normal chloroplast structure (Lu et al., 2012) and reduced internode
Blue light length (Menard et al., 2006; Nanya et al., 2012). Used alone blue light tends to reduce yield and
photosynthesis efficiency compared to red light (Lu et al., 2012; Menard et al., 2006).
There was a significant increase in carotene concentration when plants were exposed to UV light
Ultraviolet light
before harvest.

CUCUMBER

Light quality Plant response

Far-Red light Stimulated stem elongation and leaf expansion at lower R:FR (Shibuya et al., 2019). Increased stem
dry weight and sugar content (Cu et al., 2009).
Red light Increased number of leaves, root, and shoot growth (Marques da Silva et al., 2016).
Green light Increased growth, leaf area fresh and dry weight (Brazaityte et al., 2009; Samuoliene et al., 2011;
Novickovas et al., 2012) compared to high-pressure sodium (HPS) lamps.
Blue light Increased leaf area, fresh and dry weight, and photosynthetic pigments compared to natural light
and HPS lamps (Samuoliene et al., 2012). Decreased hypocotyl elongation (Novickovas et al., 2012;
Hernandez and Kubota, 2016).
UltraViolet light Positive results controlling powdery mildew (Suthaparan et al., 2017).

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PEPPER

Light quality Plant response

Far-Red light Increased plant height and stem mass compared to red light alone (Brown et al., 1995).
Red light Increased number of leaves per plant and shoot length (Marques da Silva et al; 2016; Tang et al., 2019).
Green light Increased leaf area (Samouliene et al., 2012), growth, yield phenolic and carotenoid content compared
to HPS lamps (Guo et al., 2016).
Blue light Suppressed plant growth and biomass formation compared to cool white fluorescent lamps when used
in high amounts (Hoffmann et al., 2015).

*Much of this research was conducted in germination or growth chambers. Greenhouse growers should
consider this data useful but remember that the selection of glazings, shade materials, and age of
greenhouse will have equal if not more significant impacts on light than their supplemental light sources.
Light quality can be affected by greenhouse glazing. By implementing artificial lighting we can provide a
better light recipe to improve yield and fruit quality.

LIGHT QUALITY IN VINE CROPS:

The optimal light intensity for vine crops will depend on the cultivar, environmental conditions, and stage
of development. Seedlings and young plants have different light requirements than mature crops.

Minimum DLI: 12 mol m-2 d-1

Optimum DLI for mature plants: 30 mol m-2 d-1

Photoperiod: 16 to 18 hours

* Greenhouse growers need to think about outside light levels vs inside light levels and understand
the light loss from glazing and structure. All growers need to understand that light is only one of nine
variables that impact plant growth. While the plant may be able to use high (or low) light levels, if the
other climate conditions are not in balance then crop production will not be optimal.

In order to create the perfect ambient to promote photosynthesis within artificial lighting, CO2 injection
can also be applied. Research has demonstrated CO2 enrichment can increase yield from 14% to 20%
in tomatoes (Kimball, 2000) under good light levels. When increasing CO2 levels inside of a greenhouse
environment it is necessary to consider increased levels significantly. A small increase e.g., 600 to 700
ppm does not contribute a lot to increase photosynthesis levels. In tomato is recommended to increase
CO2 levels to 800- 1200 ppm in order to see a significant increase in photosynthesis and yield.

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PHOTOPERIOD RESPONSE IN VINE CROPS
Prolonging photoperiods with supplemental light results in
increases in growth and yield for many horticultural species and
is a widely used technique in greenhouse production (Dorais
et al., 2010). Daylength also has an important influence on
rates of translocation and respiration, on the accumulation of
photosynthates, and on carbon partitioning between soluble
sugars and starch. Previous studies have shown long photoperiods
(16 h) can substantially increase leaf area, dry weight per unit leaf
area, plant height, dry weight per unit height, plant spread, and
flower-bud numbers in tomato plants.

Is important to mention, more light will not always translate to

better production. Fruiting crops require at least 4 to 6 hours of
darkness or physiological disorders such as chlorosis, reduced
plant size, and yield can occur.

CANNABIS

Cannabis is a crop that differs from other horticultural crops. This

is primarily because its yield cannot be evaluated based solely
on the weight or number of flowers or leaves. The chemical
compounds produced by Cannabis are a very important product of
this crop. In order to produce high-value Cannabis it is necessary
to understand how environmental factors can be manipulated to
enhance final product quality.

Consistent yields and quality uniformity between production cycles are important to Cannabis growers.
This has resulted in more Cannabis growers operating in controlled environment facilities. CEA
production in which temperature, humidity, light intensity, the light spectrum, and carbon dioxide (CO2)
levels can be controlled offers the ability to grow Cannabis year-round. Under stable environmental
conditions, growers can produce up to six harvests per year. This makes indoor cropping 15-30 times
more productive than outdoor cultivation (Magagnini et al., 2018).
There are several environmental factors that play key roles in controlling yield, flowering, sex of the
plants, and cannabidiol (CBD) and tetrahydrocannabinol (THC) concentrations in Cannabis. These
factors include photoperiod, light intensity, and light quality.

PHOTOPERIOD RESPONSE IN CANNABIS

Tournois (1912) was the first researcher to demonstrate that Cannabis flowering is hastened by short
days and delayed under long days. Hall (2013) also concluded that environmental factors, including
temperature and photoperiod, can influence Cannabis’ reproductive abilities. In many plants, flowering
occurs when the meristematic tissue receives signals produced by changes in temperature and/or light
duration and/or quality.

10
Sexual expression in Cannabis is largely genetic (Flachowsky et al. 2001), but can be altered by
environmental influences. Tournois was the first to report sexual reversal in the Cannabaceae family
when he observed the effects of short photoperiods on Cannabis. Tournois reported a tendency toward
maleness in Cannabis despite most dioecious plants showing a female tendency under similar light
conditions.

Many factors contribute to the sexuality of flowering Cannabis plants. Under average conditions with
a normal inductive photoperiod, Cannabis plants flower and produce approximately equal numbers of
pure male and female plants with a few hermaphrodites (both sexes on the same plant).

Under conditions of extreme stress, such as nutrient excess or deficiency, mutilation, and altered light
cycles, Cannabis plant populations have been shown to depart greatly from the expected one-to-one
male to female plant ratio (Clarke, 1999). Clarke (1999) also found that photoperiods of less than 14-16
hours can promote premature floral transition concluding Cannabis displays a quantitative short-day
response.

There are three distinct phases in Cannabis cultivation: propagation, vegetative growth, and flowering.
Recent applications for research of production purposes recommend the use of long photoperiods (18
hours) for the propagation and vegetative phases and short photoperiods (12 hours) for the flowering
phase when using artificial lighting (Magagnini et al., 2018).

LIGHT QUANTITY IN CANNABIS

Several studies with Cannabis have demonstrated that increasing the light intensity can have a positive
effect on plant photosynthesis and/or growth (Chandra et al. 2008; Potter and Duncombe, 2012;
Vanhove et al., 2011).

However, there is not always a correlation between a higher photosynthesis rate and more vegetative
growth with higher flower yields. For example, Potter and Duncombe, (2012) using different light intensity
treatments, concluded no significant difference in mass foliage or total THC levels within the foliage.
However, the same researchers reported an increase in flower yield and THC present in flowers with
increasing light intensity.

In addition, Vanhove et al (2011) demonstrated that a higher light intensity with a plant density of 16
plants per square meter can increase yield and THC concentration in comparison to lower light intensity
levels. This research also showed that the use of the same high light intensity, but under a higher planting
density (20 plants per square meter), can affect yield. Chandra et al., (2008) also reported greater net
photosynthetic and transpiration rates when the light intensity increased.

11
LIGHT QUALITY IN CANNABIS
Plant growth, morphology, and metabolism can be manipulated by changing light quality. For example,
it is known that blue light decreases internode length making plants more compact (Dong et al., 2014).
Also, several studies have demonstrated that far-red and green wavelengths induce stem and leaf
elongation (Franklin et al., 2005).

The same responses have been confirmed in a high number of crops including Cannabis. Lalge et al.
(2017) concluded that in general, red and blue light spectrums cause shorter internodes, smaller leaf
area, and more compact morphology compared to a white light source. In addition, Hawley et al. (2018),
reported a significant increase in yield and concentration of total THC when using intra canopy red and
blue lighting compared to the sunlight control treatment.

Livadariu et al. (2018) tested the use of green or blue light in Cannabis production compared to sunlight.
Results showed a significant increase in yield and THC content when using green light and an increase
in polyphenols, flavonoids, and protein under blue light treatments compared to the control sunlight
treatment.

Lyndon et al. (1987) demonstrated that THC content of some Cannabis plants can be increased by
irradiating them with UV-B light. Marti et al. (2014) also corroborated the same response in a more recent
study. However, no other Cannabis chemical compounds have been confirmed to increase under UV
treatments.

Light Quality Plant Response

Red light Significantly increased yield, tetrahydrocannabinol (THC) (Hawley et al., 2018), and
cannabidiol (CBD) (Magagnini et al., 2018) content in bud tissue.
Green light Significantly increased α-pinene, borneol (Hawley et al., 2018), and THC in bud tissue,
and antioxidant capacity compared to sunlight (Livadariu et al., 2018).
Blue light Increased polyphenols, flavonoids, fresh weight, and protein compared to sunlight
(Livadariu et al., 2018).

COMPARING LEDS AND HPS LAMPS IN CANNABIS PRODUCTION

For many years Cannabis production was done mainly with high-pressure sodium (HPS) lamps. It is now
possible to control and improve Cannabis quality using LED lamps. A recent study by Magagnini et al.
(2018) compared the production of Cannabis using HPS lamps and two different LEDs lamps (LED lamp
1: 12 percent blue, 19 percent green, 61 percent red, and 8 percent far-red. LED lamp 2:1 percent UV
light, 20 percent blue, 39 percent green, 35 percent red and 5 percent far-red). The same light intensity
of 450 μmol m-2 s-1 was used under all treatments.

Study results showed HPS lamps produced taller and higher stem dry weight compared to LED
treatments. However, HPS treatments resulted in a significant decline in THC concentration in flowers
compared to both LED treatments. Under LED light treatments plants were shorter and compact, but
showed higher CBD and THC content. This shows that the optimized light spectrum improves the value
and quality of Cannabis.

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In Hort Americas we can offer different solutions for indoor Cannabis production. The best option to
meet light quality and efficiency is the PKR L1000 LED Grow Light from Current by GE.

As mentioned previously the Arize Element L1000 is the industry’s first one-for-one LED replacement
for a double-ended 1000-watt high-pressure sodium (HPS) fixture. This lamp is the most advanced,
flexible greenhouse grow light on the market. Current worked closely with its customers to design a top
light with efficacy levels up to 3.5 micromoles per joule – making it the most efficient grow light on the
market. In addition, it supports universal installation, enabling growers to grow more and consume less
in any region.

STRAWBERRIES

Strawberry is now the crop on the spot of current research

when speaking about LED lighting for crop production.
Greenhouse production and the interest in indoor production
for strawberries are expanding every day. Therefore now
researchers are looking to learn more about the best light
quantity and quality.

LIGHT QUANTITY IN STRAWBERRY

Speaking about light intensity most updated research has
shown light intensity around 200 to 250 μmol m-2 s-1 can
have good results food indoor and supplemental lighting
on strawberries. This crop seems to be more sensitive to
high light intensity than other common crops. In greenhouse
applications we know recommended DLI levels can go from
17 to 20 mol m-2 d-1. However light intensity used in research
done in indoor facilities can point to maintaining low DLI levels
in order to have better overall results and better benefits from
the light quality provided.

LIGHT QUALITY IN STRAWBERRY

Research done by the research foundation Proefcentrum
Hoogstraten in Belgium demonstrated the importance of
Far-red light for strawberries. This research suggests that the
addition of 5% of Far- Red light to the light spectrum can be
a real advantage for strawberry plant development. A fuller,
more elongated crop is created. In this research, the best
light quality for strawberry was reported using 7% Blue, 16%
Green, 72% Red, and 5% Far-Red. More recent research has
also concluded far-red can have a good impact on yield, plant
morphology, and fruit quality.

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Light Quality Strawberry cultivar Treatment Response Reference
Far-red (700- 740 Zahedi and Sa-
Paros 735 nm / 15 μmol m-2 s-1 Increased flower number
nm) rikhani, 2016
436 nm / Light intensity: Yield increased in compar-
Blue Light (400 - Nadalini et al.,
Elsanta 100 μmol m-2 s-1 / Tem- ison to neon tubes and red
500 nm) 2017
perature 25ºC light treatments
UV Light (315 18 - 29 min per 3 days /
Albion Increased Anthocyanin Xu et al., 2017
-380 nm) 20 C
450 nm + 660 nm/ Ratio
Akihime Increased yield Nhut et al., 2003
3:7/ 60 μmol m-2 s-1 / 25ºC
Increase in yield, flavour, Hanenberg
88% red + 12% Blue / 90
Elsanta / Sonata refraction, titratable acid And Verkerke,
μmol m-2 s-1
Purple light and vitamin C content 2016
(Red + Blue) Higher fresh mass accu-
Red (661 nm) + Blue (449
mulation / 19: 1 - higher in
nm)/ 10:1 and 19:1 / Pho-
Albion inflorescences and crown
toperiod 16 h/ 120 μmol
number than the
m-2 s-1
other treatments
Light quality more suitable
Orange, red, blue/ 3:2:1
Full spectrum for strawberry’s vegetative Li et al., 2008
ratio/ 19ºC
growth

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ORNAMENTALS: ORCHIDS

Management of light inside a growing system is not only applicable to food production. Floriculture, a
discipline of horticulture, is also benefited by the application of environmental control inside growing
systems. Even though ornamentals are only used for decoration and landscaping purposes there is a
very good market in this field. With the correct preparation and investment in greenhouse-controlled
environment technologies, there is definitely an advantage when speaking about production and
quality in ornamentals, the reason why at least in the United States most ornamental production takes
place inside of greenhouses, where important environmental variables such as light can be controlled.
Ornamentals include some plants that can be very sensitive to environmental variables. A clear example
is Orchids.

Orchids are a highly valuable product recognized by their

demand in terms of light and temperature during the
vegetative and generative phases of development. Like
many ornamentals, Orchids do not like direct sunlight.
Usually, Orchids need high light levels in the dormant
phase, but during the rest of the cycle, shade must be
applied in greenhouses to reduce light intensity. Artificial
lighting can be a solution in order to provide better
lighting conditions inside growing systems. Application
of supplemental lighting treatments in Orchids has
shown that a gradual increase in light intensity can show
good results in terms of flower diameter and abortion
reduction. Research has demonstrated an increase from
40 to 160 μmol m-2 s-1 during the propagation phase
using supplemental lighting (up to 300 μmol m-2 s-1 in
flowering plants) can reduce harvest time, reduce bud
abortion, increase shoot development and increase
flower diameter from 10 to 20%.

HOW TO SELECT THE

BEST FIXTURE?
Lamp selection when speaking about plant production
in the horticulture or floriculture field is a very important
decision. Lamps can be a good investment when we
ask ourselves the correct questions. When working with
artificial lighting we first need to analyze the requirements
of our growing system and our crop.

A clear example is the different needs from an indoor

vertical farming system in comparison with top lighting
inside a plant factory or a greenhouse. Vertical farming
is mostly used for leafy greens production. In a vertical
farm, indoor system plants are grown in a multi-layer

15
system where height between plants and lamps allow the use of multiple lamps with a lower photon
flux in comparison with the ones required at the top of greenhouses or plant factories where photon flux
should be way higher in order to reach plant canopy levels at a higher distance and provide enough light
per day to optimize plant growth.

Another use of artificial lighting is the use of photoperiodic lighting. In some plants, flowering can be
triggered by short or long-day conditions. Therefore some growers can be interested in the use of
artificial lighting to create an artificial photoperiod to promote or delay flowering in different crops. Plants
can have a response to photoperiod from very low light intensity levels. Meaning not a lot of light is
required in order to promote a photoperiodic response. When your objective is mainly to create an
artificial photoperiod for your plants you can go for a more simple lamp that can provide low light
intensity levels. This kind of lamp will not have a strong impact on plant growth but will provide enough
lighting to induce a photoperiodic response.

Lamps used for indoor vertical farm systems, top lighting, and photoperiodic lighting can have very
different characteristics and prices. Therefore it is crucial to define which lamp will be the one necessary
for you based on the lighting necessities for your plants and your growing system.

Vertical farming Top lighting Photoperiodic lighting

Once you define the type of lamp required then comes to the most difficult decision. You will encounter
several options for vertical farming, top lighting, and photoperiodic lighting. How can you decide which
is the best option? What should you be looking for in a good lighting system?
A lamp with a good design can definitely mark the difference in energy savings and overall plant growth
and health. But where can you look for information in order to compare different lighting options?

DLC (Design Light Consortium) is a third-party verifier of light specs. DLC is a non-profit organization
whose mission is to achieve energy optimization by enabling interconnected solutions with a focus
on quality for people and the environment. By visiting the DLC website (https://www.designlights.
org/horticultural-lighting/technical-requirements/) you can learn the minimum technical requirements
for horticultural lighting. Also, DLC has tested and reported different LED lamps used in Horticultural
lighting and has provided a list of reliable and efficient lighting options for Horticultural lighting included
in their DLC Horticultural Lighting Qualified Products List (QPL).

Technical requirements for horticultural lighting include information about: Photosynthetic photon
flux, spectral quantum distribution, photosynthetic photon intensity distribution, efficacy, long-term
performance, warranty, electrical performance, and safety.

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Let’s explain why each of these parameters listed by DLC is important and which are minimum
requirements stated by DLC:

Photosynthetic photon flux (µmol/s): Will provide you information about the “lamp power”, meaning
how is the total output of the product per time including the light within the spectrum that is recognized
to be used by plants in photosynthesis (Defined by ANSI/ASABE S640 for PPF: 400-700nm).

Spectral Quantum Distribution (µmol/s•nm): Provides information about how much light are you
getting from a lamp but is now linked to light quality. Specifically provides information about how photon
flux is distributed across the wavelengths used by the plant for photosynthesis (400-700 nm) and the
far-red wavelength (400-800nm) which can also have an impact on plant metabolism.

Efficacy (µmol/J): Is calculated using data about the lamp output (Output of the fixture over the specific
range of wavelengths defined by ANSI/ASABE S640) and electrical input. Efficacy will basically tell you
how efficiently your lamp is performing. DLC states that in order to consider a lamp reliable and efficient
efficacy levels should be 1.81 μmol/J or higher.

Long-term performance: Can be measured by evaluating the ability of the device to maintain its output
(Measured in quanta of photons, Q) within the given ranges over time. This can be also called: Flux
Maintenance. DLC set a standard to consider a lamp reliable based on their long-term performance
evaluation: Q 90 of ≥36,000 hours within the PPF range (400-700nm).

Warranty: Provides a guarantee from the manufacturer regarding the condition of its product and can
state the reparation or replacement of product during the warranty period. DLC states a good lamp
manufacturer should provide at least a warranty of 5 years, including terms and conditions excluding
key components such as the LED, driver, or optics.

ELECTRICAL PERFORMANCE
• Power factor: Defined as the cosine of an angle between current and voltage of an Ac circuit At
lower power factor, higher is the load current and vice-versa. The power factor is important because
you may be paying for reactive power that you cannot use to power equipment. DLC states LED
lighting for horticulture use must have a measured power factor of ≥0.90 at any rated input voltage
and maximum designed output power.

• Total Harmonic Distortion, current (THDi): This is a measurement that tells you how much of
the distortion of a voltage or current is due to harmonics in the signal. Is considered an important
aspect of power systems and it should be kept as low as possible. Lower THD in power systems
means higher power factor, lower peak currents, and higher efficiency. Based on DLC technical
requirements LED lighting for horticultural practices must have a measured THDi of ≤20% at any
rated input voltage and maximum designed output power.

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 LIGHTING OPTIONS FOR INDOOR FARMING
The use of artificial lighting will be essential when growing indoor crops. In indoor production, the
whole source of light will be artificial. Therefore we must select the best lamp to promote plant growth,
development, and quality with high quality and uniform lighting. There are a lot of options when choosing
a source for artificial lighting. However, as we previously mentioned we highly recommend always looking
for a cost-effective long-last product, with enough light output for your crop and a good warranty.

Current by GE is the digital engine for intelligent environments with advanced LED technology to develop
more energy-efficient and productive lighting products.

Current by GE is working diligently to develop the best light quality options for indoor growers. The
newest lighting options for vertical farming offered by the company are the different models of GE
Arize Life 2 LED Growing System. GE Arize Life 2 is a fluorescent replacement for vertical farming
systems with all the benefits of LED technology including longer product life, energy savings, and lower
maintenance while providing optimal colors on the spectrum for plant growth. GE Arize Life 2 lamps
are designed for dense, multi-layer applications, the Arize Life 2 illuminates leafy green, microgreen, and
propagation-stage crops from seed to harvest. Offered in two lengths with nine spectral options with a
50% longer lifespan, doubled run lengths, and efficacy levels peaking at 3.2 μmol/J. The customer can
select from different light quality options based on the crop and characteristics wanted for their product.

Indoor farming includes more than just vertical farming systems. Research has demonstrated that
indoor farming production for some crops like Cannabis can improve yield and quality consistency in
comparison to open field and greenhouse production.

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Connected
Extensive work by the team at Current by GE resulted in the creation of the first true 1:1 HPS replacement:
GE Arize Element L1000. This option for top lighting has efficacy levels up to 3.5 micromoles per joule,
making it the most efficient grow light on the market, enabling growers to grow more and consume less
in any region. The L1000 will soon be available with a reproductive and balanced spectrum.

Of course, artificial lighting was not only developed for indoor production, this technology can also be
applied as Supplemental Lighting inside greenhouses.

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LIGHTING OPTIONS FOR SUPPLEMENTAL LIGHTING
APPLICATIONS
Top lighting is highly recommended for use in greenhouses located in zones with a low Daily Light
Integral (DLI). Improving the amount of light your plants are receiving in zones with a low DLI will help to
keep the normal speed of growth and improve yield in comparison to plants grown only under natural
light. Research has demonstrated that the addition of crop-specific light spectrum to the ambient
natural light that is enough to achieve optimum levels of DLI can positively affect crop quality and yield
ultimately resulting in a more valuable product. An example is a recent study was done at Michigan
State University which demonstrated that Basil grown under high light intensity has a better bitter flavor.
Furthermore, the addition of a specific light spectrum in greenhouse environments can improve the
color and texture of leafy greens.

Adding blue and red supplemental light increases biomass and yield of greenhouse-grown tomatoes
(Kaiser et al., 2019). Supplemental lighting can also improve flavor and more importantly, can help to
provide optimum light levels when natural light is lower than recommended.

Previous studies also showed, increasing 10 to 11 units of DLI (Summer-Winter) with supplemental
lighting can increase hydroponic tomato yield by 30% (Celina & Mitchell, 2016).

There are different types of light sources when speaking about supplemental lighting: High-pressure
sodium lamps, metal halide lamps, and light-emitting diodes (LEDs). LED lighting offers the option to
create light recipes to meet specific crop necessities at the highest efficiency. When selecting a lamp for
supplemental lighting in a tomato greenhouse it is important to consider the light spectrum. White light
can be a great source of light for your crop. However, let’s focus on efficiency and light intensity. When
speaking about how plants will react to light, we need to remember most light used for photosynthesis
will be located in the blue and red spectrum. Natural light present inside greenhouses is already providing
a full spectrum of light. Therefore, the advice will be to focus on the light “colors” where we know plants
will work the most when selecting a lamp for supplemental lighting purposes.

In Hort Americas we can offer different solutions for greenhouse supplemental lighting. Usually, smart
growers want to go with the most efficient spectrum. The best recommendation we can offer to meet
light spectrum, intensity, and efficiency is the PPR L1000 LED Grow Light from Current by GE. PPR
stands for Purple type R This is a red (+/-90%) blue (=/-10%) fixture. That is our most efficient spectrum
at over 3.0 umols/j and 599w.

The Arize Element L1000 is the industry’s first one-for-one LED replacement for a double-ended 1000-
watt high-pressure sodium (HPS) fixture. This lamp is the most advanced, flexible greenhouse grow light
on the market. Current worked closely with its customers to design a top light with efficacy levels up to
3.5 micromoles per joule – making it the most efficient grow light on the market. In addition, it supports
universal installation, enabling growers to grow more and consume less in any region.

FEATURES
• Efficacy of up to 3.5 μmol/J
• Dimmable (dimming switch sold separately)
• Operating temperature of up to +50°C
• Lifetime: L90 >36,000 hours
• Remote mount driver options
• UL Wet Rated & IP66
• 5-year limited warranty

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SELECTING THE BEST LIGHT
Fixtures and spectrum recommended for common horticulture crops:

Crop Stage Spectrum

Leafy greens Germination/ Propagation PPB or PKB as Blue promotes root creation. If you
want to maximize your electrical efficacy (µmol/j),
your choice is PPB. PKB will be more comfortable
to the workers’ eyes.
Leafy greens Reproductive PPR or PKR as red promotes biomass and
flowering. If you want to maximize your electrical
efficacy (µmol/j), your choice is PPB. PKB will be
more comfortable to the workers’ eyes.
Cannabis Propagation PPB or PKB because more Blue tends to keep the
crop in a vegetative state and shorter in size.
Cannabis Flowering PKR because cannabis secondary metabolite
seems to be stimulated by the green portion
of light while the low blue to red ratio seems to
promote flowering in biomass development.
Ornamentals/ Flowers PPB or PKB will work well and allow growers to
reduce plant growth regulators.
Microgreens Any spectrum will work, but high blue will keep the
seedlings from stretching.
Strawberry PKR and PKF is very safe for all berry crops.
Intensity will be most important.
Vine crops/ PPR for supplemental lighting in the greenhouse.
Academic studies (University of Arizona &
Supplemental lighting Michigan) tend to agree that the best spectrum
for greenhouse lighting is the most efficient one
in efficacy thus higher micromols/joule should be
considered. Tomatoes: PPR - Bell Peppers: PKB
(Harrow research center) - Cucumber should be
PKR. If in doubt choose PKR. It will work in every
situation.

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 QUESTIONS TO ASK WHEN SELECTING A LIGHT MANUFACTURER
Another important aspect when selecting an option for LED lighting for horticulture is the specific
information about the manufacturer: How much experience do they have? How long have been in the
lighting business? This information can be linked to how efficient and complete the service they can
provide. Horticulture lighting can be a high investment, always look for a manufacturer that can provide
enough information about their lighting system and can assist you with light spectrum selection and light
plans. Light plans will always be a good tool to understand your lighting systems, the number of fixtures,
and light uniformity over your plants. In Hort Americas we offer you a complete service starting from our
advice on the best light system from your project, recommendations on light quality, light plans along all
the technical services to support your success.

HOW TO REQUEST A LIGHT PLAN

As we mentioned, a light plan can be a very useful tool to manage lighting inside our growing system.
By requesting a light plan you can get exact information about the number of fixtures required and how
to place lamps in order to provide uniform lighting to your crop. In order to create a good and accurate
light plan, specific information about your growing system will be required. This section of the article has
the purpose to guide you on how to provide the best information in order to request a light plan with us.

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Atlantic Grown Organics
When requesting a light plan you first will need to specify the growing system used. We will provide two
options: A light plan for supplemental lighting inside a greenhouse or a light plant for a plant factory with
sole-source lighting.

SUPPLEMENTAL LIGHTING INSIDE A GREENHOUSE SYSTEM

As we learned, supplemental lighting can be a good option when natural DLI levels are below the needs
of the crops. Also can be applied to provide more uniform light to different crops and when direct
sunlight can affect our crop development. In order to create a light plan for supplemental lighting, we
will require to know about the greenhouse dimensions. Below you can learn about specific dimensions
requested from your greenhouse: Bay width, Gutter height, Section size truss spacing, total length, and
total width.

Once we have the general information about your greenhouse structure we will need to know about the
inside. When growing crops inside a greenhouse we can have different systems: Bench crops or floor
crops. We will need to know how your plants are located inside the greenhouse. Once you select a type
of system we will request specific information about your setup.

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After getting information about greenhouse dimension and
plant distribution we need to work with lighting. We will be
happy to assist you by providing advice on the type of lamp
and light quality recommended for your specific crop. The
specification required to generate light are the following:

• Light level: Provide the ideal light intensity requested by

the crop to provide the desired quantity of supplemental
lighting inside your greenhouse.

• Desired Light Source: You can select LED and HPS

lamp options. In terms of efficiency and light quality, we
recommend going for LED lamps.

• Light spectrum: This will be probably the hardest aspect

to select. The selection of light quality will be totally crop-
specific and we can provide advice in case you need it.
For example, the best recommendation we can offer for
supplemental lighting in tomato meeting light spectrum,
intensity, and efficiency is the PPR L1000 LED Grow Light
from Current by GE. PPR stands for Purple type R This
is a red (+/-90%) blue (=/-10%) fixture. That is our most
efficient spectrum at over 3.0 umols/j and 599w.

• Voltage required: It is very important to check electrical

needs for your system.

• Track/truss mounting preference: We offer different

installation options.

• Shade: Specify where your shade cloth is located Top of

the truss/ Bottom of the truss

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 PLANT FACTORY WITH SOLE-SOURCE LIGHTING
Indoor systems such as plant factories require very
different light ambient in comparison to a greenhouse
with supplemental lighting. When working with a plant
factory we will need to know what kind of system you will
be using: Vertical farming or floor production.

Different lamps are designed in order to provide better

lighting ambient in vertical farming and floor production
systems.

VERTICAL FARMING SYSTEMS

When requesting a light plan for a vertical farming system
we will first ask you to provide the following information:

• Crop: Most vertical farming systems are used for

leafy greens production or propagation. Is important
to specify the types of crop you will be growing so we
can prove full advice in the light customization.

• Light level: Provide the ideal light intensity requested by your crop. For example, Some leafy greens
like microgreens can grow in low light conditions under a DLI from 10 to 12.

• Light spectrum: We offer a variety of light spectrums that can work for vertical farming crops. Most
leafy greens can grow great under a balanced spectrum. On the other hand transplant for example
can grow better under conditions with more blue light. This will provide conditions to create more
compact and strong transplants.

• Presence of reflecting material: Reflecting material can affect light ambient. Is important to know
if your grow room is wrapped in reflective material.

Dimensions for your vertical farm are also important. We will request you to provide as much information
as possible about your setup and plant distribution.

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Farmbox Greens
INDOOR FARMING - FLOOR PRODUCTION
Indoor farming facilities with floor crops are usually used for crops like cannabis.
Light intensity and quality are very important to improve production under indoor
farming. As learned before, the best option we have for indoor production with
floor crops is L1000. We order to provide the best light plant to get uniform light
to your plants we will request the following information:

• Light level: Crops like cannabis love light. So be aware that light levels
for these crops should be high enough to push growth and development.
Crops like cannabis can tolerate from 400 μmol m-2 s-1 to even 2000
μmol m-2 s-1. In order to achieve the DLI recommended for this crop high
intensity will be required from the light source. This is why L1000 can be a
great option to provide high light intensity in the most efficient way.

• Desired Light Source: You can select LED and HPS lamp options. In
terms of efficiency and light quality, we recommend going for LED lamps.
In addition, HPS lamps can create an environment where temperature and
humidity can be more complicated to manage.

• Light spectrum: This will be probably the hardest aspect to select. For crops
like cannabis grown in indoor facilities we recommend to use in production
areas in flowering stage PKR L1000 LED Grow Light from Current by GE to
optimize plant growth, photosynthesis and by consequence yield. For the
propagation phase, we recommend PPB or PKB in order to keep plants
vegetative and more compact.

• Voltage required: It is very important to check electrical needs for your

system.

The dimension of the room, plant distribution, and height is also important to
develop a light plant. You will be asked to share the following information about
your grow room including plant distribution.

Every day we learn more about the benefits of lighting applications in horticulture. New
technologies in LED lighting now allow us to provide ideal light quality and intensity in the most
efficient way. Demonstrating improvements in our growing systems can be achieved with the
correct application. In Hort Americas we compromise to guide in every step to get the best
quality, intensity, and uniformity in light with the most efficient lamps on the market.

H O R T A M E R I C A S , L L C • 2 8 0 1 R E N E E S T. B E D F O R D , T X 7 6 0 2 1 • 4 6 9 - 5 3 2 - 2 3 8 3

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