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Supplemental Lighting Orientation and Red-to-blue Ratio of Light-emitting Diodes for Greenhouse Tomato Production


Abstract and Figures

Current greenhouse supplemental lighting technology uses broad-spectrum high-pressure sodium lamps (HPS) that, despite being an excellent luminous source, are not the most efficient light source for plant production. Specific light frequencies in the 400- to 700-nm range have been shown to affect photosynthesis more directly than other wavelengths (especially in the red and blue ranges). Light-emitting diodes (LEDs) could diminish lighting costs as a result of their high efficiency, lower operating temperatures, and wavelength specificity. LEDs can be selected to target the wavelengths used by plants, enabling growers to customize the light produced, to enable maximum plant production and limit wavelengths that do not significantly impact plant growth. In our experiment, hydroponically grown tomato plants (Solanum lycopersicum L.) were grown using a full factorial design with three light intensities (high: 135 μmol·m-2·s-1, medium: 115 μmol·m-2·s-1, and low: 100 μmol·m-2·s-1) at three red (661 nm) to blue (449 nm) ratio levels (5:1, 10:1, and 19:1). Secondary treatments for comparison were 100% HPS, 100% red LED light supplied from above the plant, 100% red LED light supplied below the plant, a 50%:50%LED:HPS mixture, and a control (no supplemental lighting). Both runs of the experiment lasted 120 days during the Summer-Fall 2011 and the Winter-Spring 2011-12. The highest biomass production (excluding fruit) occurred with the 19:1 ratio (red to blue) with increasing intensity resulting in more growth, whereas a higher fruit production was obtained using the 5:1 ratio. The highestmarketable fruit production (fruit over 90 g) was obtained with the 50%:50%LED:HPS followed by 5:1 high and 19:1 high. Consistently the 5:1 high performed well in every category. LEDs have been shown to be superior in fruit production over HPS alone, and LEDs can improve tomato fruit production when mixed with HPS. LEDs provide a promising mechanism to enhance greenhouse artificial lighting systems.
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HORTSCIENCE 49(4):448–452. 2014.
Supplemental Lighting Orientation
and Red-to-blue Ratio of Light-emitting
Diodes for Greenhouse Tomato
Paul Deram
Department of Bioresource Engineering, Macdonald Campus of McGill
University, 21111 Lakeshore Road, Ste-Anne-de-Bellevue, Quebec, H9X
3V9, Canada
Mark G. Lefsrud
and Vale
´rie Orsat
Department of Bioresource Engineering, Macdonald Campus of McGill
Additional index words. high-pressure sodium, intercanopy lighting, photosynthesis, supple-
mental lighting
Abstract. Current greenhouse supplemental lighting technology uses broad-spectrum
high-pressure sodium lamps (HPS) that, despite being an excellent luminous source, are
not the most efficient light source for plant production. Specific light frequencies in the
400- to 700-nm range have been shown to affect photosynthesis more directly than other
wavelengths (especially in the red and blue ranges). Light-emitting diodes (LEDs) could
diminish lighting costs as a result of their high efficiency, lower operating temperatures,
and wavelength specificity. LEDs can be selected to target the wavelengths used by plants,
enabling growers to customize the light produced, to enable maximum plant production
and limit wavelengths that do not significantly impact plant growth. In our experiment,
hydroponically grown tomato plants (Solanum lycopersicum L.) were grown using
a full factorial design with three light intensities (high: 135 mmol·m
115 mmol·m
, and low: 100 mmol·m
) at three red (661 nm) to blue (449 nm)
ratio levels (5:1, 10:1, and 19:1). Secondary treatments for comparison were 100%
HPS, 100% red LED light supplied from above the plant, 100% red LED light supplied
below the plant, a 50%:50% LED:HPS mixture, and a control (no supplemental lighting).
Both runs of the experiment lasted 120 days during the Summer–Fall 2011 and the Winter–
Spring 2011–12. The highest biomass production (excluding fruit) occurred with the 19:1
ratio (red to blue) with increasing intensity resulting in more growth, whereas a higher
fruit production was obtained using the 5:1 ratio. The highest marketable fruit production
(fruit over 90 g) was obtained with the 50%:50% LED:HPS followed by 5:1 high and 19:1
high. Consistently the 5:1 high performed well in every category. LEDs have been shown
to be superior in fruit production over HPS alone, and LEDs can improve tomato fruit
production when mixed with HPS. LEDs provide a promising mechanism to enhance
greenhouse artificial lighting systems.
Tomatoes are one of the most important
horticultural crops in the world. According to
Statistics Canada, tomato sales accounted for
close to 50% of the total fruit and vegetable
sales in the country in 2011 (Statistics Canada,
2011). Tomato sales in Canada reached
$496 million, an increase of 5.5% since 2010
(Statistics Canada, 2011). Greenhouseproduc-
tion exceeded field-grown tomatoes in 1997,
and in 2003, the greenhouse production was
more than nine times that of field-grown
tomatoes (Cook and Calvin, 2005). Today
there are 23 million m
allocated to green-
house fruit and vegetable production in
Canada with sales exceeding $1.1 billion
annually (Statistics Canada, 2011). Accord-
ing to Brazaityt_
e et al. (2009), in countries
of high latitude (e.g., Canada), tomatoes are
almost exclusively grown in greenhouses.
Light irradiance is the limiting factor for in-
creasing production in greenhouses, when
all other factors (temperature, nutrient levels,
and water availability) are adequately main-
tained (Smith, 1982). Ohashi-Kaneko et al.
(2007) state that artificial lighting permits
stable vegetable crop production no matter
the environmental conditions (with a favor-
able temperature in the greenhouse). Green-
houses in northern latitudes must compensate
for the attenuation in total light availability
(from prolonged winter with short daylight
hours), and supplemental artificial lighting
is required to maintain a consistent crop
yield throughout the Canadian winters. Con-
ventional greenhouse lighting systems use
broad-spectrum light sources such as HPS or
fluorescent lamps. LEDs have been shown to
decrease artificial lighting costs to less than
25% of the cost of traditional artificial light-
ing as a result of their 75% higher electrical
conversion efficiency (Gomez et al., 2013).
HPS lamps were tailored for human vision
and therefore are not ideally suited for plant
growth (Bula et al., 1991).
Earlier research has shown that the most
important wavelengths for photosynthesis are
in the blue and red wavelengths; peaks in
photosynthetic efficiency are found at 440
(blue), 620 (red), and 670 (red) nm (± 10 nm)
(McCree, 1972). The rapid improvement in
LED technology has been driving research in
plant production in recent years (Brazaity_
et al., 2009). Xiaoying et al. (2012) reported
new LEDs with a bandwidth of ± 15 nm,
permitting for much better focus on the most
efficient wavelengths for photosynthesis. The
wavelength specificity, small mass (less than
1 g each), small volume, relatively cool emit-
ting temperature, longevity of over 100,000 h,
and linear photon output are all characteris-
tics that make LEDs better suited for crop
production than earlier greenhouse lighting
systems (Folta et al., 2005).
Different wavelengths of the light spec-
trum have been found to have specific effects
on plant morphology, physiology, photosyn-
thesis efficacy, and flowering capabilities
(Menard et al., 2006). Although light is the
primary source of energy for photosynthesis,
it is also a vital regulator of many photo-
sensory circuits in plants. Blue light and red
light trigger different circuits and gene ex-
pression, which can have both positive and
negative effects on the growth and develop-
ment of plants (O’Carrigan et al., 2014). Thus,
research is focusing more on proper combi-
nations of light (Massa et al., 2008). Okamoto
et al. (1996) reported that both red and blue
light can be used by chlorophyll during photo-
synthesis and explained that blue light is
beneficial to plant morphology and overall
health. Blue light (450 nm) has been shown to
heavily suppress stem elongation in multiple
plant species (Okamoto et al., 1996) but also
increases plant biomass and fruit yield in
tomato and cucumber plants (Menard et al.,
2006). Herna´ndez and Kubota (2012) reported
that at the tomato seedling stage, red light is
sufficient to grow tomato seedlings and that
the addition of blue light is unnecessary. Over-
all, blue light is not as effective for photosyn-
thesis as red light, because it inhibits leaf
growth by reducing cell expansion and re-
duces the total amount of chlorophyll in the
leaves (Goto, 2003). As a result of this lower
efficiency, researchers tend to undervalue the
use of blue light and not consider it in high
proportions for plant growth (Goto, 2003).
A lack of blue light has been shown to have
adverse effects on plant morphology: low
number of chloroplasts, lower thickness of
cell walls, and low spongy mesophyll tissues
Received for publication 30 Aug. 2013. Accepted
for publication 8 Jan. 2014.
This work was supported by General Electric Light-
ing Solutions Canada and the Natural Sciences and
Engineering Research Council of Canada (NSERC)
(CRDPJ project no. 418919-11). We thank Claire
Boivin for her tomato growing expertise.
Associate Professors.
To whom reprint requests should be addressed;
(Goto, 2003). Boccalandro et al. (2012) show
that blue light promotes leaf expansion, sto-
matal opening, and chloroplast relocation
through phototropin activation in Arabidop-
sis and other higher plants. Blue light was
shown to stimulate stomata opening and in-
crease the rate of photosynthesis by up to
30% in some species (Menard et al., 2006).
Blue light from LED sources was also shown
to be highly efficient at protecting crop plants
from many pathogens as well as increasing
antioxidants and osmoprotectant produc-
tion (Kim et al., 2013). Plant response to
light from the red and the blue spectra has
been documented extensively (Menard et al.,
2006). The ratio of blue to red light is shown
to be the most important factor when using
LEDs, because having both blue light and red
light increases plant biomass growth and fruit
production by over 20% when compared with
having only one of the wavelengths (Brazaityt_
et al., 2009; Goto, 2003; Lefsrud et al., 2008;
Xiaoying et al., 2011, 2012).
This experiment used LED prototypes from
General Electric Lighting Solutions Canada
(Lachine, Quebec, Canada), where the over-
all goal of the project was to determine which
ratio and intensity combinations best suit to-
mato plants for fruit production under green-
house applications. Previous studies performed
at McGill University (Martineau et al., 2012;
Schwalb, 2013) have shown that the ratios
of red to blue light used for this experiment
increased plant photosynthetic rate at the
seedling stage and this research would con-
firm that these same ratios result in improved
fruit and biomass production for mature
Materials and Methods
Tomato plants (S. esculentum cv. Trust
were grafted onto S.hirsutum cv. Maxifort)
(Ontario Plant Propagation, St. Thomas,
Ontario, Canada) were obtained 55 d after
seeding and were hydroponically grown in
a greenhouse setting following similar cul-
ture methods to the industrial practices of
Savoura (Les Serres Du St-Laurent Inc.,
Portneuf, Quebec, Canada) using a modified
full-strength Hoagland nutrient solution
(Savoura proprietary information) (Deram,
The air temperature ranged from 21.8 ±
2.4 C during the day and 16.9 ± 3.4 C
during the night (average of both experimen-
tal runs). The LED light arrays were turned
on from 0600 to 2200 HR for a total photo-
period of 16 h. The nutrient solution was
supplied through drip irrigation (14257 Bio-
floral, Montreal, Quebec, Canada) for 3 min
out of every 20 min (19 L·h
) for a total ir-
rigation of 6 L per plant per day (based
on 1 mL per 1 J of irradiance). The plants
were pollinated by hand, shaking the flowers
with a cotton-tipped swab three times a week.
A central computer in the greenhouse controlled
the lights, irrigation, and ventilation coupled
with a misting system for cooling. Relative
humidity was monitored but was not controlled.
Average daily relative humidity reached a
high of 82% ± 5% and a low of 30% ± 10%
(average of both experimental runs).
The LED light arrays were prototypes
(1.78 m ·8cm·2 cm) with wavelengths
of 449 nm for blue light and 665 nm for red
light. Twelve ratio and intensity-specific LED
prototypes were used, nine of which were
used to set up a full factorial with three ratios
of red to blue (5:1, 10:1, and 19:1) and three
intensities (high: 135 mmol·m
, medium:
115 mmol·m
, and low: 100 mmol·m
measured and confirmed at the beginning and
end of each replicate with less than 2% drift
during replicates. The light sensor used was
the underwater spherical quantum sensor
(LI-193; Li-COR, Lincoln, NE); an explana-
tion on why this sensor was chosen can be
found in the ‘‘Results and Discussion’’ sec-
tion. The remaining prototypes, used for further
experimental treatments, were two 100% red
light arrays (red top and red bottom at the
high intensity of 135 mmol·m
) and a 10:1
medium (for use in the 50%:50% LED:HPS,
combined irradiance at 135 mmol·m
Three HPS lamps (Philips SON-T Master
600W, Amsterdam, The Netherlands) were
used, one for the 50%:50% LED:HPS and two
for the 100% HPS section (135 mmol·m
The control section did not have any supple-
mental lighting. The red bottom treatment
lights were placed at the bottom of the section
(at the level of the first leaves) and shone
upward into the plant canopy, whereas the red
top LEDs were placed at the top, similar to all
other treatments.
A greenhouse section (7.6 m ·12 m set
in a north–south orientation) with long wire
mesh tables (1.2 m in height) was used. The
tables were separated into 14 sections (2 m ·
1 m), each one for a specific light treatment.
Three lamps were installed per section, mak-
ing space for two rows of plants between
them. The lamps were set at an intercanopy
level (10 cm below the top of the plants) and
raised weekly to maintain relative height,
except for the red bottom treatment, where
the lamps were kept at the height of the first
double layer of 2.44 m high (8 feet) 80%
shadecloth (8MK808; Harnois, St-Thomas,
Quebec, Canada), preventing 96% of light
from passing through. A single layer of
2.44 m (8 feet) 60% shadecloth (8MK608;
Harnois) was installed above all of the sections
during the first replicate (summer months) to
simulate winter conditions.
Two experimental replicates, summer (July
to Oct. 2011) and winter (Jan. to Apr. 2012),
were performed with two harvest times, one
at 70 d and one at 120 d. Half the plants were
randomly selected and harvested at 70 d, and
the remaining plants continued the experi-
ment for the full 120 d. A 2-month period was
allotted between the experimental replicates
to minimize the risk of pathogens carrying
over. The location of each light treatment in
the greenhouse was randomly allotted at the
beginning of each experimental replicate.
Eight plants (six during the second experi-
mental replicate, because the Savoura plants
were larger and the same plant density was
kept) were placed in each section, in two
rows, between the lamps. The individual
plants were measured as individual replicates
between seasons. The change in plant number
(from eight to six) did not have any effect on
the statistical analysis of the reported values.
At harvest, fresh weight was determined
by separating and weighing both aerial plant
biomass (the rooting system was discarded)
and fruit biomass. All fruit greater than 2 g
were counted and weighed (fruit under 2 g
were included as plant biomass). Ripe fruit
was harvested throughout the experiment at
the first observed red pigmentation (consid-
ered ripe), counted, and individually weighed.
Plants were pruned according to Savoura’s
methods (every 2 weeks, Savoura unpublished
data) with fresh and dry biomass measured
for each plant. The marketable fruit value
was set at 90 g and is an internal standard for
Savoura signifying marketable fruit. The
fresh biomass harvested (aerial and fruit)
was dried according to the ASABE (2007)
standard with a temperature of 65 C for no
less than 72 h and subsequently weighed.
Main effects were analyzed by one-way
analysis of variance with the standard Tukey-
Kramer test (a#0.05) applied to determine
significant differences between treatments.
The relationship between the experiment’s
dependent variables and treatments was de-
termined by regression analysis. As a result
of the strong constraints of the experiment
(large plant variability, limited space, limited
time, large number of different factors need-
ing testing), the power of the statistical anal-
ysis was calculated post hoc to be between
10% and 38% depending on the quantity being
Results and Discussion
The point source nature of the LED arrays
makes it difficult to measure the light in-
tensity with conventional light-measuring
devices. Typical spectroradiometers and light-
measuring devices are built to measure light
levels from the sun or other light sources that
disperse light in every direction (such as HPS
lighting) and therefore are not as compatible
with the LED arrays. A series of irradiance
tests were performed with a range of different
light measuring devices to find the most ap-
propriate solution for measuring the LED
point source arrays. All light measurements
were taken at horizontal, vertical, and 45at
three different heights and three points along
the length of each light fixture. The first test
was performed using a pyranometer (total
solar radiation) (MP-100; Apogee Instruments,
Logan UT) and a quantum meter (measures
only the photosynthetically active radiation)
(MQ-100; Apogee Instruments). It was found
that the light measurement from both devices
was variable (30% differences in readings)
under weighing blue light and over weighing
red light (Apogee Instruments Inc., 2012a,
2012b); they may not properly report wave-
lengths outside the 460- to 660-nm range, and
therefore they could not be used for the exper-
iment. A spectroradiometer (BLACK-Comet
Concave Grating Spectrometer; StellarNet
Inc., Tampa, FL) was then tested. The spec-
troradiometer was much more reliable than
the quantum meter and pyranometer, but the
same problem with variability resulting from
spatial position was found. The spectroradi-
ometer was designed for conventional over-
head light sources and only records light
coming from directly above the sensor. The
field of view of a typical spectroradiometer
was shown to be 10(MacArthur et al., 2007).
With adjustments to the positioning (directly
facing the LED for the measurements), a light
map could be created using the spectroradi-
ometer, but it was still not as reliable as
expected for measurements of the light re-
ceived by the plants.
An underwater spherical quantum sensor
(LI-193; Li-COR) was tested. The spherical
quantum sensor was developed to capture
light dispersion in underwater biological ex-
periments by measuring the photon flux com-
ing from all directions. This sensor was chosen
as a result of its ability to record the photon
flux coming from all directions, which was
well suited for measuring the LED lighting in
this experiment (because the LED arrays do
not result in a wide dispersion of light). The
measurements of the light from all angles
above a theoretical horizontal surface resulted
in no significant reduction in reported values.
This underwater spherical light sensor was
well adapted to the LED fixtures and gave us
much more accurate measurements of the
lighting with less than 5% variability be-
tween measurements. However, it should be
noted that when the handle of the light sensor
was parallel to the light source (or above the
theoretical horizontal surface), the light mea-
surement was 20% lower than when placed
perpendicular to the light source. Despite the
20% loss in reading light perpendicular to the
sensor, the underwater quantum sensor was
found to be the most accurate sensor for this
research and a well-adapted sensor to LED
testing. No statistical difference was measured
between the initial and final light readings or
between the intensities of treatments at the
same intensity level. The average daily light
integral (solar and artificial) was 21 mol·d
37 mol·d
for the summer run and 42 mol·d
20 mol·d
for the winter run.
Results from the experiment revealed that
the five highest number of fruit-producing
light treatments were 5:1 high (385 fruit), 5:1
medium (358 fruit), 5:1 low (341 fruit), 19:1
high (315 fruit), and 100% LED (310 fruit).
The control was statistically significantly dif-
ferent from all five of the high producing
treatments. The average number of fruit per
plant is shown in Figure 1. The 5:1 ratio was
the highest producing ratio from this exper-
iment with all three intensities leading the
ranking for most fruit produced. The 5:1 ratio
being the highest fruit-producing ratio in this
experiment agrees with research from Goto
(2003) and Menard et al. (2006), who found
that blue light promoted flowering and fruit-
ing, but contradicts Miyashita et al. (1995),
who reported that red light, and not blue light,
would increase flowering. With regard to
fruit mass, 5:1 high (27.2 kg), 5:1 medium
(25.8 kg), 19:1 high (24 kg), 50%:50%
LED:HPS (23.3 kg), and red top (23.2 kg)
were the five highest treatments. No statisti-
cal differences were measured between any
of the treatments with the exception of the
control, which was statistically different from
all five of the high producing treatments. The
average fruit mass per plant is shown in
Figure 2. The highest five treatments for
marketable number of fruit were 50%:50%
LED:HPS (with a total of 118 fruit over 90 g),
red top (115 fruit), 5:1 medium (113 fruit),
19:1 high (109 fruit), and 5:1 high (104 fruit).
The highest five total marketable fruit mass
were the same treatments but in a different
order: 50%:50% LED:HPS with 17.4 kg fol-
lowed by 5:1 high with 16.3 kg, 19:1 high with
16.2 kg, red top with 15.8 kg, and 5:1 medium
with 15.6 kg. Fifty percent:50% LED:HPS
was one of the highest producing treatments
for marketable fruit and agrees with research
from Menard et al. (2006) that shows that
supplementing blue and red light to HPS
creates much higher production than with
HPS alone. The differences between the high-
est treatments were not statistically different,
but all highest producing treatments were
statistically different from the control. The
average marketable fruit mass per plant is
shown in Figure 3.
The high irradiance level was the highest
producer for all ratios, both for vegetative bio-
mass and for fruit production. As expected from
the literature, higher intensities bring forth
more production (McAvoy, 1984; Tennessen
et al., 1994) with all ratios producing more
under higher irradiance levels.
The five highest treatments for both fresh
biomass and dry biomass were 19:1 high and
red bottom and included the other 19:1 treat-
ments (medium and low) and the 100% red
top. For fresh weight, they were 19:1 high had
37.8 kg followed by red bottom with 37.4 kg,
50%:50% LED:HPS with 34.5 kg, and 10:1
medium with 33.9 kg. The average fresh
biomass per plant is shown in Figure 4. For
dry mass, 19:1 high had 2.8 kg followed by
Fig. 1. Average number of fruit per plant per light treatment. The data were separated into three categories.
Best: over 19 fruit (in black). Average: from seven to 19 fruit (in dark gray). Poor: under seven
marketable fruit (in light gray). Statistically significant differences were observed between the best
category and the poor category.
Fig. 2. Average fruit mass per plant (kg) per light treatment. The data were separated into three categories.
Best: over 1.9 kg of fruit (in black). Average: from 0.2 kg to 1.9 kg of fruit (in dark gray). Poor: under
0.2 kg of fruit (in light gray). Statistically significant differences were observed between the best
category and the poor category.
red bottom at 2.7 kg, 5:1 high at 2.5 kg, and
19:1 medium at 2.5 kg. This result is sup-
ported by the literature that shows that red
light produces more biomass (Brown et al.,
1995; Hoenecke et al., 1992), because all
treatments with high red light were found
consistently to be the highest. The largest
fresh and dry vegetative biomass occurred
with the 19:1 high LED.
A fruit mass-to-plant fresh biomass ratio
was calculated as shown in Figure 5. The five
highest ratio treatments were 5:1 low (0.87
fruit to biomass), 5:1 high (0.82), 5:1 medium
(0.79), red top (0.75), and 10:1 high (0.71).
The control ratio was 0.12. All 5:1 intensity
levels as well as 10:1 high, red top, and
50%:50% LED:HPS were found to be statis-
tically different from the control treatment.
The 5:1 ratio treatments (high, medium, and
low) were shown to be statistically different
from treatments 10:1 low and 19:1 low (the
two lowest after control).
For the marketable fruit mass-to-plant
fresh biomass ratio, the five highest treat-
ments were red top (0.49), 5:1 high (0.49),
50%:50% LED:HPS (0.48), 5:1 low (0.49),
and 5:1 medium (0.46). The control ratio
was measured at 0.09. Statistically significant
differences were observed between the red
top and 5:1 high treatments with the control
only. Fruit-to-biomass ratio provides infor-
mation on the amount of vegetative biomass
the plant produced relative to fruit produc-
tion. This ratio is important, because it shows
how efficient the plant was at producing fruit
from the resources given. A higher value is
more desirable, because it shows that a higher
proportion of the plant growth was turned
into the marketable product.
The red top and the red bottom treatments
were directly compared with each other. The
major difference between the two treatments
was the setup with the red bottom treatment
lights placed at the bottom of the section and
shone upward into the plant canopy, whereas
the red top LEDs were placed at the top,
similar to all other treatments. The red bottom
had slightly less light levels than the red top.
Overall, the red bottom section slightly under-
fruiting categories but created more biomass.
No statistical differences were measured be-
tween these two treatments. The differences
between the two treatments are more pro-
nounced toward the end of the run. These
differences could be explained by the lower
light levels or because the plants in the red
bottom section grew more side stems and
suckers close to the LED arrays and did not
grow as tall (observed but not measured).
However, no conclusions can be drawn from
the statistics, and the production results were
similar for both treatments. This result could
suggest that the light coming from below was
at least as beneficial as the light coming from
above (Moss, 1964).
From the regression analysis of the facto-
rial experiment, it can be reported that higher
levels of light increased production, whereas
increased levels of red light (relative to blue)
resulted in less fruit:
Number of Fruit ¼23:9 + Intensity0:12
+ Light Ratio4:5ðÞR2¼0:68
where intensity is the amount of light in the
treatment (100 mmol·m
for low, 115
for medium, 135 mmol·m
for high) and light ratio is the ratio of red light
to blue light (1 for 5:1, 2 for 10:1, and 3 for
19:1, chosen in sequence).
The regression analysis also indicated
that increased levels of light resulted
in increased biomass, and increased red
Fig. 3. Average marketable fruit mass per plant (kg) per light treatment. No statistically significant
differences were observed.
Fig. 4. Average fresh weight of plant biomass (excluding fruit) per light treatment (kg). No statistically
significant differences were observed.
Fig. 5. Total fruit mass-to-plant biomass ratio per light treatment. Statistically significant differences
between the best category and the poor category; also between the highest two (5:1 low and 5:1 high)
and the treatments under 0.4 (10:1 low and 19:1 low).
light (relative to blue) resulted in more
Vegetative Fresh Biomass in gramsðÞ
¼1982:2 + Intensity5:1
+ Light Ratio426:3R
where intensity is the amount of light in the
treatment, in mmol·m
(100 for low, 115
for medium, 135 for high) and light ratio is
the ratio of red light to blue light (1 for 5:1, 2
for 10:1, and 3 for 19:1).
Overall, it was shown that the highest
producing LED treatments (5:1 high, 5:1 me-
dium, 19:1 high, and 5:1 low) and 50%:50%
LED:HPS consistently outperformed the HPS
treatment alone, and thus these treatments
can be considered an improvement over tra-
ditional HPS lighting for greenhouses. Al-
though no significant differences were found
between the higher performing treatments,
5:1 high consistently performed well in every
category. As expected from the literature, it
was found that an increase in light intensity
brought higher production of both fruit mass
and plant biomass, and an increase in red light
increased biomass production and slightly
lowered the amount of fruit production.
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... In greenhouse tomato (Solanum lycopersicum) production, photosynthesis and carbon sequestration may be hindered by cloud cover, shading systems, and variable solar radiation, as well as by plant mutual shading (e.g., when high vertical stem training or increased crop densities are used) (Zhang et al., 2015;Tewolde et al., 2018). Considering the non-uniform distribution of solar radiation around the world, limitations may also occur in cases of high-latitude countries such as Canada, Japan, Norway, as well as in the northern areas of China and the United States, where long winters and low DLIs (daily light integrals) may affect greenhouse production (Garland et al., 2010;Deram et al., 2014;Sun et al., 2015;Tewolde et al., 2016;Paponov et al., 2019). Supplemental artificial lighting can be applied to increase greenhouse yields and ensure stable year-round production regardless of environmental conditions (Ohashi-Kaneko et al., 2007), even in regions with high DLIs, such as the Mediterranean and Jordan Valley (Israel) (Joshi et al., 2019;Paucek et al., 2020). ...
... Greenhouse tomatoes represent one of the most relevant horticultural crops worldwide (Deram et al., 2014;FAO, 2018). In intensive greenhouse tomato production, high-wire single-truss training systems are normally applied to enable labor reductions, multiple harvests and possible automation (Giniger et al., 1988;Okano et al., 2001). ...
... Only observations reporting a control, either with solar or solar + HPS light, were used for the meta-analysis after a second selection phase. In one case (Deram et al., 2014), the comparison between the control and treatment showed extremely high values compared to other results. In this case, the data were considered outliers and were excluded from the meta-analysis. ...
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Intensive growing systems used for greenhouse tomato production, together with light interception by cladding materials or other devices, may induce intracanopy mutual shading and create suboptimal environmental conditions for plant growth. There are a large number of published peer-reviewed studies assessing the effects of supplemental light-emitting diode (LED) lighting on improving light distribution in plant canopies, increasing crop yields and producing qualitative traits. However, the research results are often contradictory, as the lighting parameters (e.g., photoperiod, intensity, and quality) and environmental conditions vary among conducted experiments. This research presents a global overview of supplemental LED lighting applications for greenhouse tomato production deepened by a meta-analysis aimed at answering the following research question: does supplemental LED lighting enhance the yield and qualitative traits of greenhouse truss tomato production? The meta-analysis was based on the differences among independent groups by comparing a control value (featuring either background solar light or solar + HPS light) with a treatment value (solar + supplemental LED light or solar + HPS + supplemental LED light, respectively) and included 31 published papers and 100 total observations. The meta-analysis results revealed the statistically significant positive effects (p-value < 0.001) of supplemental LED lighting on enhancing the yield (+40%), soluble solid (+6%) and ascorbic acid (+11%) contents, leaf chlorophyll content (+31%), photosynthetic capacity (+50%), and leaf area (+9%) compared to the control conditions. In contrast, supplemental LED lighting did not show a statistically significant effect on the leaf stomatal conductance (p-value = 0.171). In conclusion, in addition to some partial inconsistencies among the considered studies, the present research enables us to assert that supplemental LED lighting ameliorates the quantitative and qualitative aspects of greenhouse tomato production.
... In addition, the present results also demonstrate that spectral composition also affected green mass and yield production, resulting in the highest green mass and the lowest yield at low light dominated by the red spectral region. Similar results were found in tomato plants grown at different red/blue ratios, where the biomass production was the highest at a high proportion of red light, whereas the highest fruit production was obtained at a high proportion of blue light (Deram et al., 2014). It appeared that a low amount of blue light (at low light intensity with red dominant spectra) stimulates green mass production, whereas a sufficient amount of blue light can improve yield. ...
... Since leaf numbers did not change significantly (data not shown), the blue and green lights mainly affected the stem elongation. The blue light-induced inhibition of stem elongation was also demonstrated in bell pepper (Claypool and Lieth, 2020), tomato seedlings (Deram et al., 2014), and in chrysanthemum (Kim et al., 2004). The inhibitory effect of blue light on stem elongation was also presented inversely by Runkle and Heins (2001), who reported that environments deficient in blue light promoted internode elongation in several long-day plants as compared to unfiltered sunlight with a similar daily light integral. ...
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Chili is widely used as a food additive and a flavouring and colouring agent and also has great importance in health preservation and therapy due to the abundant presence of many bioactive compounds, such as polyphenols, flavonoids, carotenoids, and capsaicinoids. Most of these secondary metabolites are strong antioxidants. In the present study, the effect of light intensity and spectral composition was studied on the growth, flowering, and yield of chilli together with the accumulation of secondary metabolites in the fruit. Two light intensities (300 and 500 μmol m–2 s–1) were applied in different spectral compositions. A broad white LED spectrum with and without FR application and with blue LED supplement was compared to blue and red LED lightings in different (80/20 and 95/5%) blue/red ratios. High light intensity increased the harvest index (fruit yield vs. biomass production) and reduced the flowering time of the plants. The amount of secondary metabolites in the fruit varied both by light intensity and spectral compositions; phenolic content and the radical scavenging activity were stimulated, whereas capsaicin accumulation was suppressed by blue light. The red colour of the fruit (provided by carotenoids) was inversely correlated with the absolute amount of blue, green, and far-red light. Based on the results, a schematic model was created, representing light-dependent metabolic changes in chilli. The results indicated that the accumulation of secondary metabolites could be modified by the adjustment of light intensity and spectral composition; however, different types of metabolites required different light environments.
... Subsequent declines of LED prices have led to commercial crop cultivation in closed, environmentally controlled facilities known as vertical farms Benke and Tomkins, 2017;O Sullivan et al., 2019 and plant factories with artificial lighting Kozai, 2013;Kozai et al., 2020 , which use numerous LEDs as light sources to drive photosynthesis, resulting in overwhelmingly high planting density, high growth rates, and high crop quality Orsini et al., 2020 . Field and greenhouse cultivations also use LEDs for purposes such as supplemental lighting for photosynthesis support Deram et al., 2014;Hikosaka et al., 2013 , photomorphogenesis modification Cope andBugbee, 2013;Jeong et al., 2014 , metabolite synthesis activation Kitazaki et al., 2018;Kopsell et al., 2014;Piovene et al., 2015 , andpest management Cochard et al., 2019;Stukenberg et al., 2015 . In addition to visible light of the 400 -700 nm wavelength range required for maintenance of the basic physiology of plants, far-red Shibuya et al., 2019;Zhang and Runkle, 2019 for photomorphogenesis and ultraviolet light Huché-Thélier et al., 2016 for metabolite synthesis are wavelength bands that improve crop quality. ...
This study investigated a light sensor function of light-emitting diodes (LEDs), the use of which is expanding in plant cultivations. Unimodal spectral LEDs of four types with respective emission peak wavelengths of 464, 501, 634, and 849 nm, and a white LED with a bimodal spectrum with 455-nm primary and 574-nm secondary peaks were used for this study. Open circuit voltage (VOC) of up to 1-2 V was induced in the LEDs when they were irradiated with sunlight. The VOC value of the 634 nm LED saturated with a low photon flux density can be used for binary discrimination between daylight and night. Each LED had a VOC inducible threshold wavelength of incident light. By virtue of the wavelength threshold feature, existence of a plant leaf between a light source and the LEDs is detectable by comparing the VOC values of blue-green range LEDs (464 nm, 501 nm) and near-infrared (NIR) LEDs (849 nm). Under leaf shadow, the NIR LED VOC exceeded those of the blue-green range LEDs. Under natural incident sunlight, the VOCs of the blue-green range LEDs were greater than that of the NIR LED. Another function of LEDs in agricultural use has been demonstrated.
... Even though highpressure sodium lamps (HPS) are an excellent light source, they are not the most efficient in obtaining high yield. LED lamps can be adjusted to emit only certain wavelengths, to maximize plant yield (Deram et al., 2014). Paucek et al. (2020), demonstrated that supplementing natural light with LED in 'Siranzo' tomatoes grown in hydroponic system in the Mediterranean climate, accelerated fruit maturation with one week during the spring and two weeks during summer. ...
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In this research, biochemical analyses were monitored by determination at the level of tomato plants and fruits, within a protected growing environment (vegetation house), before and after the application of light provided by LEDs in red, blue and monochrome white, in addition to natural light, during the summer (June, 3rd decade-August 3rd decade, 2019). In parallel with the analysis of tomato plants, the substrates from the pots corresponding to the plants were analyzed. Values obtained for tomato plants of the analyzed varieties (Solanum lycopersicum L. cv. ʻSonia de Buzauʼ, cv. ʻCoralinaʼ and cv. ʻHeraʼ) after 2 months of cultivation, regarding the content in mineral elements of non-metabolized forms (nitrates N-NO3, ppm (phosphates P-PO4, ppm, and K + ppm), showed a good supply of them, fact that determined their normal development in the protected cultivation area. The obtained biochemical results were situated within the limits accepted by the scientific literature, but were differentiated in correlation with the tomato genotype, LED light and daily exposure time, compared to control plants (unexposed to additional LED light). The fruits formed at the level of the first fruiting stage, toward the end of the experimental period, were analyzed together with the mineral elements and their contents in acidity %, soluble carbohydrates (%) and vitamin C (mg/100 g fresh product). The response to the applied treatment ensured uniform fruiting yield, after exposure to the treatment for 45 minutes/day with monochrome LEDs for all three colors, in the case of ʻCoralinaʼ tomato assortment, compared to the other 2 study varieties.
... However, the choice of RB ratio depends on the plant and plant parameters of concern. The RB ratio of 2 to 5 is considered apt for most vegetative and medicinal plant growth [19], [20]. Most photoreceptors mainly use the Red and Blue (RB) spectrum. ...
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Healing of various ailments using herbal medicines is gaining much interest. Plants classified as grasses, specifically Cynodon dactylon, are an appreciated group of monocots used in many herbal remedies. In this work, C. dactylon, is grown naturally and also under market available LED Luminaires with different lighting conditions. Until 2010, most of the plants were grown under conventional lamps that are not spectrally tunable. Cynodon dactylon, the grass, was grown under two different light spectrum, two light levels and three photoperiods (9hours, 12 hours, 15 hours) to extend our experiential knowledge. The biomass accumulation was highest when grown under a lower RB ratio-12-hour-163μmol/s, and phenolic content was highest at 92.8 mg/g wt Gallic Acid Equivalents under combined light source at 15-hour photoperiod. A spectrally tunable LED light source with an optimal quantity of LEDs saves cost, space and energy. Considering the light parameters from the light sources used for growing C. dactylon, Levenberg–Marquardt (LM) algorithm is implemented to select an optimal LED quantity that composes the light source. The algorithm simulates the given target spectrum with minimum fitness error. The method applied to model LEDs, its validation against the practical LED spectrum, spectrum matching and computation of Luminous flux, Photosynthetic Photon Flux and efficacy is also presented. Many spectrums were simulated to validate the performance of the algorithm. A solution of optimal LEDs for three Photosynthetic Photon Flux (PPF) levels with LEDs derived, and it is observed that the number of LEDs increased with PPF.
... Las longitudes de onda de los LEDs fueron: azul de 450 a 480 nm con un máximo en 465 nm, roja de 620 a 650 nm con un máximo en 635 nm y blanco con un espectro de luz de 400 a 700 nm, las cuales estaban dentro del rango indicado por Deram et al. (2014) quienes señalaron que la combinación de luz azul (425-490 nm) y luz roja (610-700 nm) son los mejores espectros de luz para la fotosíntesis de las plantas. Las longitudes de onda emitidas por los LEDs se midieron con un espectroradiómetro (CS-2000, Konica Minolta ® , Japón). ...
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La combinación de diodos emisores de luz (LEDs) rojos y azules es una fuente de luz efectiva para el crecimiento y desarrollo de las plantas. Diversas especies del género Lilium son valoradas como flores de corte, pero la información que se tiene del efecto de la calidad de la luz sobre su crecimiento es aún muy escasa y es necesario determinar el espectro de luz óptimo que permita obtener características deseables. El objetivo de este trabajo fue evaluar el crecimiento de Lilium spp. ‘Corvara’, con iluminación LED. La proporción de luces LED roja y azul en cada tratamiento fue: 20:80 (R4B); 40:60 (2R3B); 60:40 (3R2B); 80:20 (4RB) y el testigo (W) con 100% de luz blanca. Todos los tratamientos tuvieron una radiación fotosintéticamente activa de 90 ±10 μmol m-2 s-1 durante un fotoperiodo de 14 h. El trabajo se realizó en Chapingo, México en 2019 y 2020. Los resultados mostraron que con la iluminación del tratamiento 2R3B se registró la menor cantidad de días a madurez de cosecha (91 días) y las plantas de menor altura (83 cm). Respecto al testigo se lograron incrementos en las siguientes variables: con el tratamiento R4B, área foliar 26% y color de tépalos 13% en la variable Croma; con 3R2B la vida en florero 6%, con 4RB, altura de plantas 21%, diámetro de flor 5% y el número de días a madurez fue 16. Se concluye que la proporción de la luz roja y azul modifica el crecimiento y desarrollo de las plantas de Lilium spp. ‘Corvara’.
... Although the role of carotenoids in photosynthesis is well appreciated, wavelengths other than red and blue had rarely been used in academic studies on the effect of LED lightings in tomato production. Consequently, there is a lot of information about the effect of red and blue light used as overhead-lighting, interlighting or hybrid-lighting (LEDs + HPS) on plant growth and yield of tomatoes (Dueck et al., 2011;Hogewoning et al., 2012;Gajc-Wolska et al., 2013;Gomez et al., 2013;Deram et al., 2014;Gómez and Mitchell, 2015;Tewolde et al., 2016;Gilli et al., 2018;Lanoue et al., 2019;Paponov et al., 2019). These studies showed that photosynthesis under a combination of red and blue light tends to be higher than under HPS lighting, but fruit yield is equal. ...
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Light emitting diodes (LEDs) are an energy efficient alternative to high-pressure sodium (HPS) lighting in tomato cultivation. In the past years, we have learned a lot about the effect of red and blue LEDs on plant growth and yield of tomatoes. From previous studies, we know that plants absorb and utilize most of the visible spectrum for photosynthesis. This part of the spectrum is referred to as the photosynthetically active radiation (PAR). We designed a LED fixture with an emission spectrum that partially matches the range of 400 to 700 nm and thus partially covers the absorption spectrum of photosynthetic pigments in tomato leaves. Tomato plants grown under this fixture were significantly taller and produced a higher fruit yield (14%) than plants grown under HPS lighting. There was no difference in the number of leaves and trusses, leaf area, stem diameter, the electron transport rate, and the normalized difference vegetation index. Lycopene and lutein contents in tomatoes were 18% and 142% higher when they were exposed to the LED fixture. However, the ß-carotene content was not different between the light treatments. Transpiration rate under LED was significantly lower (40%), while the light use efficiency (LUE) was significantly higher (19%) compared to HPS lighting. These data show that an LED fixture with an emission spectrum covering the entire PAR range can improve LUE, yields, and content of secondary metabolites in tomatoes compared to HPS lighting.
... Variuos studies have shown a species-depending plant response to LED lighting in comparison to HPS or fluorescence lamps (FL). Positive effect of blue and red LED light was determined for tomato biomass at higher light intensity (Deram et al., 2014), fresh and dry mass of lamb's lettuce (Wojciechowska et al., 2015), leaf and root mass of Petunia (Currey and Lopez, 2013). However, some few studies also reported no difference for growth response, e.g., with Chinese cabbage (Avercheva et al., 2009), Boston lettuce (Martineau et al., 2012), lettuce (Shen et al., 2014), Impatiens or Pelargonium (Currey and Lopez, 2013), or rose (Bergstrand et al., 2016) when comparing LED lighting to high intensity discharge (HID) lighting. ...
The objective of our studies was to determine changes of growth and quality of red pak choi microgreens depending on different irradiance level of LED and HPS lighting under indoor and greenhouse conditions. Microgreens of red pak choi (Brassica rapa var. chinensis 'Rubi F1') were grown in a peat substrate (pH 5-6) in 0.5 L plastic vessels for 10 days, from sowing to harvest. Day/night temperatures of 21±2/17±2°C in growth chambers and 20±3/16±3°C were established with a 16-h photoperiod and relative humidity of 50-60%. LED lighting equipment was composed of 20 units of custom-made lamps. Each lamp was designed using red LEDs (spectrum peak wavelength ' 662 nm) and blue LEDs (spectrum peak wavelength ' 451 nm). Reference microgreens were grown under HPS lamps. The photosynthetic photon flux density (PPFD) of LEDs and HPS lamps was 150, 200, 250 and 300 µmol m‑2 s‑1. For the LED lamps, red to blue light ratio was 91:9. ICP-OES method was used for determination of mineral elements, potentiometric method for nitrate content, and spectrophotometric for total anthocyanins and phenols, ascorbic acid, and DPPH. Our results revealed different effects of HPS and LED lamp illuminations under indoor and greenhouse conditions. LED lamps resulted in decrease of elongation of red pak choi microgreens under all PPFD in greenhouse, but opposite results were obtained under indoor conditions. LED lamps illumination decreased nitrate content under both growing conditions. PPFD had no effect on fresh weight, however higher PPFD of LED lamps increased it indoors. It was determined that all irradiance levels of LED lamps no effect on ascorbic acid, total phenols, DDPH; however, an increase in total anthocyanins and a decrease in macro elements were determined indoors. The opposite effect was observed in greenhouse grown plants.
... Its role has also been introduced as somehow similar to far-red light (Bernier and Périlleux, 2005). Therefore, with the sensitivity of plant phytochromes to red light, it can be said that they stimulate or stop flowering, which influences the rate of flowering in plants (Deram et al., 2014). ...
Plant growth and development under natural conditions are affected by genetic and environmental factors. In the absence of genetic constraints, growth and development of the plants are determined by environmental factors such as nutrition, planting date, and lighting conditions. Among the factors mentioned, light is not the only necessary element; however, it plays an essential role in plant metabolism. The effects of light quality can be very different; therefore, a change in that can have a huge effect on plant growth, especially on photosynthesis. Nowadays, in this new age, due to significant technological advances and the increasing demand of human societies for the production of healthy and high quality products, the use of light-emitting diodes (LEDs) as an influential factor in the production of horticultural products, especially in greenhouses, is increasing rapidly. Furthermore, lighting systems play an important role in commercial greenhouse production, particularly in the commercial vegetable production sector and in reducing electricity costs. It should be noted that red and blue lights are of great importance for plant growth. There has been a lot of research done on the effects of light spectra on plant growth and development over the past years, which shows the significance of both blue and red spectra; nevertheless, what combination with what percentage works best, is still being investigated. Nonetheless, as it has been shown so far, the effects of the combined application of these two spectra on growth parameters such as height, surface and the number of leaves, fresh and dry weight of plant body and biomass, flowering, photosynthesis, transpiration, stomatal conductance, carbohydrates and starch have been proven in most plants including vegetables, medicinal herbs, and ornamental plants. Therefore, with the proper use of blue and red spectra combination, the production efficiency can be significantly increased.
The chloroplast structural alteration and the photosynthetic apparatus activity of cherry tomato seedlings were investigated under dysprosium lamp [white light control (C)] and six light-emitting diode (LED) light treatments designated as red (R), blue (B), orange (O), green (G), red and blue (RB), and red, blue, and green (RBG) with the same photosynthetic photon flux density (PPFD) (≈320 μmol·m-2·s-1) for 30 days. Compared with C treatment, net photosynthesis of cherry tomato leaves was increased significantly under the light treatments of B, RB, and RBG and reduced under R, O, and G. Chloroplasts of the leaves under the RB treatment were rich in grana and starch granules. Moreover, chloroplasts in leaves under RB seemed to be a distinct boundary between granathylakoid and stromathylakoid. Granathylakoid under treatment B developed normally, but the chloroplasts had few starch granules. Chloroplasts under RBG were similar to those under C. Chloroplasts under R and G were relatively rich in starch granules. However, the distinction between granathylakoid and stromathylakoid under R and G was obscure. Chloroplasts under O were dysplastic. Palisade tissue cells in leaves under RB were especially well-developed and spongy tissue cells under the same treatment were localized in an orderly fashion. However, palisade and spongy tissue cells in leaves under R, O, and G were dysplastic. Stomatal numbers per mm2 were significantly increased under B, RB, and RBG. The current results suggested blue light seemed to be an essential factor for the growth of cherry tomato plants.
Recent irradiance level improvements in light-emitting diode (LED) technology has allowed this equipment to compete as suitable replacements to traditional highpressure sodium (HPS) lamps in hydroponics growth environments. The current study compares LED and HPS lighting technologies for supplemental lighting in a greenhouse at HydroSerre Mirabel (Mirabel, Quebec, Canada) for the growth of Boston lettuce (Lactuca sativa var. capitata). The light treatments were applied for 2 hours before sunset and 8.5 hours after sunset to extend the photoperiod to 18 hours. An average total light irradiance (natural and supplemental) of 71.3 mol·m-2 for HPS and 35.8 mol·m-2 for LED were recorded over the 4 weeks of each experimental run. Wet and dry biomass of the shoots was recorded. On average, HPS light treatments produced significantly similar shoot biomass compared with LED light treatment, although the LED lamps provided roughly half the amount of supplemental light compared with the HPS lamps during the 4 weeks of the experimental treatment. Analysis of the lettuce samples showed no significant difference in concentrations of β-carotene, chlorophyll a, chlorophyll b, neoxanthin, lutein, and antheraxanthin among the light treatments; however, violaxanthin concentrations showed a statistical difference resulting from light treatment. When measured on an energy basis, the LED lamps provide an energy savings of at least 33.8% and the minimal "regular" HPS provided an energy savings of 77.8% over the HPS treatment.
Red light emitting diodes (LEDs, peak wavelength: 660 nm) and white fluorescent lamps were used as light sources for growth of potato plantlets in vitro. Red (630-690 nm) photon flux (R-PF) on the empty culture shelf were adjusted at 11, 15, 28, 47 or 64 μ.mol m-2 s-1. Photosynthetic photon flux (PPF) on the empty culture shelf was adjusted at 100 μ.mol m-2 s-1 in all the treatments. Potato plantlets were cultured on Murashige &Skoog (1962) medium with or without sugar at an air temperature of 25°C and a photoperiod of 16 h. Shoot length and chlorophyll concentration of the plantlets increased with increasing R-PF, while there were no significant differences in dry weight and leaf area of the plantlets regardless of R-PF levels. Red light affected the morphology rather than the growth rate of potato plantlets in vitro. Red LEDs can be used for controlling plantlet morphology in micropropagation.
Electric supplemental lighting can account for a significant proportion of total greenhouse energy costs. Thus, the objectives of this study were to compare high-wire tomato (Solanum lycopersicum) production with and without supplemental lighting and to evaluate two different lighting positions + light sources [traditional high-pressure sodium (HPS) overhead lighting (OHL) lamps vs. lightemitting diode (LED) intracanopy lighting (ICL) towers] on several production and energy-consumption parameters for two commercial tomato cultivars. Results indicated that regardless of the lighting position + source, supplemental lighting induced early fruit production and increased node number, fruit number (FN), and total fruit fresh weight (FW) for both cultivars compared with unsupplemented controls for a winter-to-summer production period. Furthermore, no productivity differences were measured between the two supplemental lighting treatments. The energy-consumption metrics indicated that the electrical conversion efficiency for light-emitting intracanopy lighting (LED-ICL) into fruit biomass was 75% higher than that for HPS-OHL. Thus, the lighting cost per average fruit grown under the HPS-OHL lamps was 403% more than that of using LED-ICL towers. Although no increase in yield was measured using LED-ICL, significant energy savings for lighting occurred without compromising fruit yield.
Light-emitting diodes (LEDs) have tremendous potential as supplemental or sole-source lighting systems for crop production both on and off earth. Their small size, durability, long operating lifetime, wavelength specificity, relatively cool emitting surfaces, and linear photon output with electrical input current make these solid-state light sources ideal for use in plant lighting designs. Because the output waveband of LEDs (single color, nonphosphor-coated) is much narrower than that of traditional sources of electric lighting used for plant growth, one challenge in designing an optimum plant lighting system is to determine wavelengths essential for specific crops. Work at NASA's Kennedy Space Center has focused on the proportion of blue light required for normal plant growth as well as the optimum wavelength of red and the red/far-red ratio. The addition of green wavelengths for improved plant growth as well as for visual monitoring of plant status has been addressed. Like with other light sources, spectral quality of LEDs can have dramatic effects on crop anatomy and morphology as well as nutrient uptake and pathogen development. Work at Purdue University has focused on geometry of light delivery to improve energy use efficiency of a crop lighting system. Additionally, foliar intumescence developing in the absence of ultraviolet light or other less understood stimuli could become a serious limitation for some crops lighted solely by narrow-band LEDs. Ways to prevent this condition are being investigated. Potential LED benefits to the controlled environment agriculture industry are numerous and more work needs to be done to position horticulture at the forefront of this promising technology.
Supplemental lighting is proven to increase transplant growth and quality in vegetable nursery greenhouses. To evaluate plant responses to supplemental LED light quality, tomato seedlings ('Komeett') were grown in a greenhouse (Tucson, AZ, USA) until the second true leaf stage with 55.5±1.4 μmol m-2 s-1 photosynthetic photon flux of supplemental LED lighting (18-hour photoperiod). Treatments consisted of different red:blue photon flux ratios (1) 100% red:0% blue, (2) 96% red:4% blue, (3) 84% red:16% blue and a control without supplemental lighting. These ratios were evaluated under low and high daily solar light integrals (DLI) (8.9±0.9 and 19.4±1.9 mol m-2 d-1, respectively) created by different shade screens deployed in the greenhouse. Growth and morphological parameters including dry shoot mass, leaf count, stem diameter, hypocotyl length, leaf area, and chlorophyll concentration indicated the benefit of supplemental light, especially under low DLI, but there were no significant differences among different red:blue ratios regardless of DLI. The seedlings also exhibited the same high photosynthetic capacity measured under 1000 μmol m-2 s-1 PPF, ambient temperature and CO2 concentration regardless of the red:blue ratios. From this preliminary study it seems that for 'Komeett' tomato seedlings grown in greenhouse, use of 100% red LED supplemental lighting was sufficient and no additional blue light was required regardless of DLI.
In the last 15 years, extensive studies on supplemental lighting of greenhouse crops have been realized. HPS lamps are the most commonly used type of light source in greenhouse production, and PPF and photoperiod recommendations for different species have been proposed. While they have an appropriate light spectrum for photosynthesis and a high efficiency, HPS lamps are relatively poor in blue and far-red compared to the solar PPF radiation. Moreover, extended or continuous lighting provided by HPS lamps may lead to physiological disorders for some species such as tomato. It is well known that spectral quality influences plant growth and development. For example, high ratios of red to far-red can stimulate phytochrome response (stem elongation, flowering, stomatal conductance or plant anatomy), while blue light is important in the formation of Chl, chloroplast development, activation of the circadian rhythm of photosynthesis, enzyme synthesis, and photomorphogenesis. The primary objective of this study was to compare the developmental and physiological changes in tomato and cucumber plants grown under HPS with different levels of blue light, and to evaluate the use of blue LEDs for extended and inner canopy lighting. Tomato (Lycopersicon esculentum 'Trust') and cucumber (Cucumis sativus 'Bodega') plants were grown under HPS lamps with or without blue LEDs (455 nm) for 12 or 20-h photoperiods. Plant development and biomass, gas exchange measurements (ACO2, gs, Ci), light (A/Q) and CO2 (A/Ci) response curves, and Chl a fluorescence parameters have been measured weekly (cucumber) or bimonthly (tomato). Results showed that adding blue light inside the canopy increased plant biomass and fruit yield but did not offset the negative effect of extended photoperiod. Inner canopy lighting with high level of blue light was useful for cucumber but not for tomato.
The effects of light quality on biomass and internal quality of leaf lettuce, spinach and komatsuna were examined. The plants were grown hydroponically in an environmentally controlled room with a 12-h light period and under a light/dark temperature of 20 ± 1°C/18 ± 1°C and a photosynthetic photon flux density (PPFD) of 300 μmol m-2 s-1 under four light quality treatments, i.e., red light from red fluorescent lamps (R) or blue light from blue fluorescent lamps (B) or a mixture of R and B (RB) or white light from white fluorescent lamps (W). The irradiation of R compared with W increased shoot dry weight in komatsuna and decreased the nitrate content in spinach. Irradiation of B or RB compared with W increased the L-ascorbic acid content in leaf lettuce and komatsuna and decreased the nitrate content in leaf lettuce. Irradiation of B was not suitable for the spinach cultivation due to an extremely decreased shoot dry weight although the carotenoid content was slightly increased. Our data show that controlling light quality is useful to achieve higher productivity or higher nutritional quality of the commercial crops even under limited light intensity in controlled-environment agricultural facilities although the effective light quality treatment differs depending on the plant species.