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Basic Science – Research Article
Med Cannabis Cannabinoids 2018;1:19–27
The Effect of Light Spectrum on the
Morphology and Cannabinoid Content of
Cannabis sativa L.
Gianmaria Magagnini
a Gianpaolo Grassi
a Stiina Kotiranta
b
a Council for Agricultural Research and Economics, Research Centre for Cereal and Industrial Crops (CREA-CI),
Rovigo, Italy; b Valoya Oy, Helsinki, Finland
Received: March 14, 2018
Accepted: March 26, 2018
Published online: June 12, 2018
Gianpaolo Grassi
Council for Agricultural Research and Economics
Research Centre for Cereal and Industrial Crops (CREA-CI)
IT–45100 Rovigo (Italy)
E-Mail gianpaolo.grassi @ crea.gov.it
© 2018 The Author(s)
Published by S. Karger AG, Basel
E-Mail karger@karger.com
www.karger.com/mca
DOI: 10.1159/000489030
Keywords
Cannabis sativa L. · LED · Light spectrum · Cannabinoid
content
Abstract
Cannabis sativa L. flowers are the main source of Δ-9-
tetrahydrocannabinol (THC) used in medicine. One of the
most important growth factors in cannabis cultivation is
light; light quality, light intensity, and photoperiod play a big
role in a successful growth protocol. The aim of the present
study was to examine the effect of 3 different light sources
on morphology and cannabinoid production. Cannabis
clones were grown under 3 different light spectra, namely
high-pressure sodium (HPS), AP673L (LED), and NS1 (LED).
Light intensity was set to ∼450 µmol/m2/s measured from
the canopy top. The photoperiod was 18L: 6D/21 days during
the vegetative phase and 12L: 12D/46 days during the gen-
erative phase, respectively. At the end of the experiment,
plant dry weight partition, plant height, and cannabinoid
content (THC, cannabidiol [CBD], tetrahydrocannabivarin
[THCV], cannabigerol [CBG]) were measured under different
light treatments. The experiment was repeated twice. The 3
light treatments (HPS, NS1, AP673L) resulted in differences
in cannabis plant morphology and in cannabinoid content,
but not in total yield of cannabinoids. Plants under HPS treat-
ment were taller and had more flower dry weight than those
under treatments AP673L and NS1. Treatment NS1 had the
highest CBG content. Treatments NS1 and AP673L had high-
er CBD and THC concentrations than the HPS treatment. Re-
sults were similar between experiments 1 and 2. Our results
show that the plant morphology can be manipulated with
the light spectrum. Furthermore, it is possible to affect the
accumulation of different cannabinoids to increase the po-
tential of medicinal grade cannabis. In conclusion, an opti-
mized light spectrum improves the value and quality of can-
nabis. Current LED technology showed significant differenc-
es in growth habit and cannabinoid profile compared to the
traditional HPS light source. Finally, no difference of flower-
ing time was observed under different R:FR (i.e., the ratio be-
tween red and far-red light). © 2018 The Author(s)
Published by S. Karger AG, Basel
Introduction
Cultivating Cannabis sativa L. (Cannabaceae) differs
from other horticultural plants by the end product that is
harvested. The total yield cannot be rated only by the
weight of the flowers; the chemical composition of the
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Magagnini/Grassi/Kotiranta
Med Cannabis Cannabinoids 2018;1:19–27
20
DOI: 10.1159/000489030
end product is also in the interest of the producers and
end users. Different cannabis chemotypes contain nu-
merous chemical compounds, such as cannabinoids,
which are known to exert various pharmacological ef-
fects. Morphology and cannabinoid profile are depen-
dent on genetic and environmental factors. For a medici-
nal cannabis producer, a continuous and uniform yield
and production of a specific cannabinoid compound or a
ratio between the different cannabinoids throughout the
canopy and between growth cycles is important. There-
fore, more and more professional medicinal cannabis
producers are moving from greenhouses to indoors, into
controlled and closed growth chambers. In growth cham-
bers, it is possible to adjust temperature, humidity, light
intensity, light spectrum, and air CO2 concentration. One
of the most important growth factors in cannabis cultiva-
tion is light. Light quality, light intensity, and photope-
riod play a significant role in a successful growth proto-
col. Growing indoors also improves the pest management
and reduces the susceptibility of the crop to natural con-
ditions, such as bad weather. In addition to the environ-
mental factors, the regulatory authorities also increasing-
ly push licensed producers towards producing, packag-
ing, and labeling their products indoors at the producer’s
site. As said, indoor production offers the ability to culti-
vate year round under stable conditions resulting in up to
6 harvests per year. This makes indoor cropping 15–30
times more productive than outdoor cultivation [1]. Also,
the historically illegal nature of cannabis has pushed the
cultivation inside into artificial environments due to the
fear of being caught committing a crime [2]. In addition
to the positive effects of environmental control, indoor
production minimizes the risk of cross-pollination with
other nearby crops, particularly industrial hemp, to guar-
antee flowers without fertilization or seed maturation. On
the other hand, indoor cannabis cultivation is energy in-
tensive due to the high light demand and cooling of the
closed environment. Cannabis is a plant adapted to high
irradiance levels and warm temperatures. Chandra et al.
[3] demonstrated that the highest photosynthetic effi-
ciency was achieved under ∼1,500 PPFD (Photosynthet-
ic Photon Flux Density) and 25–30°C; however, there is
no evidence that a higher photosynthesis rate equals
higher flower yields. It is also questionable whether such
a high light intensity (1,500 PPFD) is economically fea-
sible in terms of energy costs put into lighting and cool-
ing. Indoor cannabis agriculture has in fact been classified
as one of the “most energy intensive industries in the
U.S.” [4]. Lighting alone consumes 79–86% of the total
electricity use [5, 6] in the cannabis farms. It has been cal-
culated that 1% of the total energy consumption in the
USA is for cannabis cultivation, and in top production
states, such as California, the equivalent value is 3% [6].
Often, cannabis production sites have separate facilities
or rooms for each growth phase due to the different pho-
toperiods and other environmental demands. There are
3 distinct phases in cannabis cultivation: propagation
phase, vegetative growth phase, and flowering phase. In
the interview study conducted by Sweet [7], it was noted
that 600–1,000 W high-pressure sodium (HPS) lights
were the most commonly used lighting source in Wash-
ington State during the flowering phase. In contrast, a
wide variety of lighting types were reported to be used in
the vegetative rooms, such as fluorescent light bulbs (CFL
or T5), metal halide bulbs (MH), HPS lamps, induction
bulbs, light-emitting diodes (LED), or a combination of
different lighting types. During the propagation phase,
the most commonly used lighting source is fluorescent
light [8]. When using older technology, such as HPS or
fluorescent light, the spectrum is seldom adjusted accord-
ing to the plants’ needs: the technology has been origi-
nally developed for totally different applications, such as
street or office lighting. In the horticulture and crop sci-
ence industry, it has been long known that one can ma-
nipulate plant morphology and metabolism with the light
spectrum. For example, blue light has been shown to de-
crease internode length and enhance compactness of
various species [9, 11], whereas far-red and green wave-
lengths have been shown to induce shade avoidance syn-
drome symptoms, including stem and leaf elongation
and premature flowering [12]. A recently published paper
from the Czech Republic also concluded that cannabis
plants grown under a red and blue light spectrum had
shorter internodes and a smaller leaf area compared to a
white light source [13]. However, the paper does not give
more specific information about the spectra used. In ad-
dition to morphological changes, light spectrum and ir-
radiance level also have an impact on plant metabolism.
The plant receives signals from the light environment
through photoreceptors. Phytochromes, cryptochromes,
phototropins, and UVR8 are the most well-studied pho-
toreceptor groups found in higher plants. Phytochromes
are the red- and far-red-sensing photoreceptors which
regulate, for example, flowering, shade avoidance syn-
drome behavior, and germination in many species. Cryp-
tochromes and phototropins are regulated mainly by blue
and green wavelengths [14, 15]. UVR8 is responsible for
UV-B-induced responses. Short wavelength irradiation
has been shown to enhance the plant defense mechanism
by inducing metabolic activity, such as phenolic com-
Light Spectrum and Cannabis sativa L.
21
Med Cannabis Cannabinoids 2018;1:19–27
DOI: 10.1159/000489030
pound synthesis. Phenolic compounds, including antho-
cyanins, found especially in red-colored leaves, have been
shown to accumulate in lettuce leaves under short-wave-
length blue and UV light. Many phenolic compounds are
part of the plants’ defense mechanism, which are synthe-
sized under environmental stress. Short-wavelength ir-
radiation and high photon flux irradiance are examples
of light-related environmental stress. Several cannabi-
noids have also been suggested to be involved in the plant
defense mechanism and to have antioxidant properties,
including Δ-9-tetrahydrocannabinol (THC) and canna-
bidiol (CBD) [16] as well as cannabigerol (CBG) [17].
Bouquet [18] hypothesized that cannabis resin has a pro-
tective sunscreen function. However, the glands and the
secreted resin are accumulated on the lower leaf surface
instead of the upper surface and in the perigonial bracts
in the inflorescence which should be more susceptible to
sun light [19]. While light quality may have an effect on
the cannabinoid synthesis, cannabis yields are thought to
strongly correlate with increasing light intensity [3, 20].
However, light intensity did not seem to affect the can-
nabinoid concentration when plants were grown under
different light intensities under HPS light [21, 22]. In the
studies by Vanhove et al. [22] and Potter and Duncombe
[21], it was concluded that THC concentrations of flower
material could be primarily linked to cannabis variety in-
stead of cultivation method. In both studies, an increasing
irradiance level correlated positively with flower dry
weight, which resulted in higher total cannabinoid yield
in the high irradiance treatments. However, the effects of
different light qualities, or spectral composition, on can-
nabinoid synthesis and concentration in floral parts re-
main elusive. There are no recent light-related studies
conducted with cannabis and based on cannabinoid pro-
files. However, already in very early studies in 1983,
Mahlberg and Hemphill [23] concluded that in different
light environments it was possible to manipulate the can-
nabinoid content of C. sativa L. measured in young leaves.
The authors used colored filters to alter the light spectrum
and concluded that the THC content of leaves from plants
grown under shaded daylight and filtered red and blue
light did not differ significantly from the THC content in
daylight controls, while leaves from plants grown under
filtered green light and darkness contained significantly
lower levels of THC than those from plants grown in sun-
light. The research and equipment at that time was not
specific enough to thoroughly explain the effect of wave-
length areas on cannabinoid content and the effect of
lighting conditions on cannabis potency is still not clear.
The first study related to light quality and cannabinoid
content was conducted by Fairbairn and Liebann [24],
who concluded that no increase of cannabinoids was
found in a Nepalese variety grown in a greenhouse with
or without supplemental lighting (HPS or UV lamps).
Cannabis growers have been interested in UV light for a
long time; however, the relationship between cannabi-
noids and UV-B is not as direct as first proposed. In-
creased concentrations of THC, but not of other canna-
binoids, were found with UV-B treatment in both leaf and
floral tissues of drug-type plants [20, 25]. In contrast,
none of the cannabinoids in fiber-type plants were affect-
ed by UV-B radiation. In a more recent study, hemp
leaves were exposed to UV-C radiation and analyzed for
changes in secondary metabolite biosynthesis [26]. While
no remarkable change in the cannabinoid content was
observed, significant increases in dehydrostilbenes and
cinnamic acid amide derivatives were found. The limited
data available on the appropriate light source for cannabis
production underscore the importance of studying tech-
nological developments in horticultural lighting. The ob-
jective of this study was to examine the effects of light-
spectral quality on cannabis morphology and cannabi-
noid content in the female flowers under artificial growing
conditions. Two lighting technologies (HPS and LED)
and 3 different light spectra were used in this study.
Materials and Methods
Unrooted C. sativa L. cuttings, drug chemotype “G-170”
(CREA-CI, Rovigo, Italy), were inserted into rockwool cubes
(Grodan, Roermond, The Netherlands) and grown under T8 fluo-
rescent lights (LUMILUX T8 36/840 and FLUORA T8 36W; Os-
ram GmbH, Munich, Germany) for 2 weeks in a climate-con-
trolled growth chamber. Light intensity during the rooting period
was ∼160 µmol/m²/s measured with UPRTek PAR200 Spectrom-
eter (UPRTek, Miaoli County, Taiwan). The spectral photon dis-
tribution of the fluorescent light source is shown in Figure 1. The
cuttings were kept under 90% relative humidity at 25°C and ex-
posed to 24 h of light. Cuttings were watered with clean tap water
at the start of the rooting period. After 3 days, cuttings were sup-
plemented daily with the complete fertilizer Coco A and B (5%
NO3–, 0.1% NH4+, 4% P2O5, 3% K2O, 7% CaO, 3% MgO, 2% SO3,
0.007% B, 0.001% Cu, 0.02% Fe DTPA, 0.0003% Fe EDTA, 0.01%
Mn, 0.002% Mo, 0.007% Zn, 0.5% fulvic and humic acid; CANNA
International BV, Oosterhout, The Netherlands) with 1.5 mS/cm
of electrical conductivity (EC) and pH 5.8. The adjustment of pH
was done by 40% nitric acid. After rooting, plants were transplant-
ed into 1.6-L pots containing coco peat (Coco Professional Plus,
CANNA International BV) and acclimatized for 8 days in a grow
room under HPS lights. Light intensity during the acclimatization
period at canopy height was 40–50 µmol/m2/s. During acclimati-
zation, plants were irrigated with a fertilization solution of EC 1.8
mS/cm and pH 5.8. After acclimatization period, 16 plants were
placed under each light treatment in the growth boxes, 48 plants
Magagnini/Grassi/Kotiranta
Med Cannabis Cannabinoids 2018;1:19–27
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DOI: 10.1159/000489030
in total. Three different light sources were used in the experiment
as treatments: 2 LED light spectra, AP673L and NS1 (B100, Valoya
Oy; Helsinki, Finland), and 1 HPS light source (Philips Master T-
PIA Greenpower 600 W; Philips, Eindhoven, The Netherlands)
with magnetic ballast (ETI, Madrid, Spain). Light fixtures were
installed in grow tents (1.2 × 1.2 × 2 m) with a Mylar interior
(DR120, Secret Jardin; Manage, Belgium), equipped with an air
exhaust system to maintain the temperature at 26°C during the
light phase and a relative humidity of 60–70% (Vents VK 125,
Vents, Kiev, Ukraine). The light irradiance level was measured to
be 450 μmol/m2/s at canopy height when plants were transferred
into the grow tents. Lamps were raised during the experiment as
plants grew taller to maintain equal light intensities (450 μmol/
m2/s in the range of 400–700 nm) throughout the experiment. Per-
centages of wavelength areas in each spectrum are presented in
Table 1. During the acclimatization and vegetative phases, the pho-
toperiod was set to 18 h of light. The duration of the vegetative
phase was 13 days. Out of the 16 plants in each treatment, 9 plants
were selected for their good condition and uniformity and kept in
the grow tents for another 46 days under a short photoperiod
(12 h light and 12 h darkness) for flower induction. During the
short photoperiod, EC of the nutrient solution was increased from
1.8 to 2.0 mS/cm. The harvested plants were cut from the base and
dried at 30°C by hanging them upside down in a dark room
equipped with a dehumidifier. The plant height, stem weight, stem
diameter, leaf biomass, and flower biomass were recorded from
each plant. The floral cannabinoid concentrations (tetrahydrocan-
nabivarin [THCV], THC, CBD, and CBG) were measured using
gas chromatography (GC) according to the community method
for the quantitative determination of THC content in hemp variet-
ies (Reg. CE 796/2004) with some modifications. 40 mg of cured
and dried flower powder was weighed in a vial tube, and 4 mL of
internal standard/extracting solution (ethanol with 0.01% of praz-
epam) was added. The sample was sonicated for 15 min at 65°C,
and the extract centrifuged at 12,000 rpm for 5 min; a 1-mL aliquot
of the extract was then transferred from the tube to a 2-mL glass
GC vial. GC analyses were performed using a SHIMADZU GC-
2010 PLUS equipped with an autosampler (H-TA srl. model HT
300 series) and a flame ionization detector (FID-2010 PLUS). The
GC column was a 30 m × 0.25 mm I.D. with 0.25-µm film (RESTEK,
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
Relative intensity, %
380 400 500 600 700 780
Wavelenght, nm
AP673L
Fluorescent tubes
HPS
NS1
Table 1. Spectral properties and the light intensities (in PAR, range
400–700 nm) under each light treatment
Light treatment
HPS AP673L NS1
300–400 1% 0% 2%
400–500 8% 14% 24%
500–600 68% 20% 37%
600–700 21% 59% 33%
700–800 3% 7% 4%
400–700 PAR 96% 93% 94%
R:FR 2.80 6.07 10.05
B:G 0.29 1.76 0.74
B:R 0.10 0.26 0.80
NS1 and AP673L are LED lights; HPS, high-pressure sodium.
R:FR and B:G ratios are calculated according to Sellaro et al. [44]:
R:FR (650–670 nm/720–740 nm), B:G (420–490 nm/500–570 nm).
Fig. 1. Relative spectral photon flux of the light sources utilized.
Light Spectrum and Cannabis sativa L.
23
Med Cannabis Cannabinoids 2018;1:19–27
DOI: 10.1159/000489030
model Rxi-5ms). Data were recorded using Labsolutions LC/GC
5.51 (SHIMADZU) software. GC conditions used for the determi-
nation of cannabinoids were: H2 at 30 mL/min as carrier gas and
N2 as make up gas at 40 mL/min, and air at 400 mL/min, respec-
tively. The split flow rate was 15.8 mL/min, split ratio 25: 1, pres-
sure 12.76 psi, and purge flow rate 3 mL/min. 1-µL injections were
used; injector and detector temperatures were 280 and 300°C, re-
spectively. The isothermal oven temperature was 240°C and the
total run time was 15 min. Quantitation was achieved by determin-
ing peak area ratios of the analytes to the internal standard versus
concentrations in the range of 7.8–500 μg/mL. The growth exper-
iment was repeated twice. The first experiment took place in April
and May 2015 and the second experiment was conducted between
February and April in 2016. The average temperature and relative
humidity (mean ± standard deviation) in the first experiment were
23.6 ± 2.8°C and 64.5 ± 14% for treatments AP673L and NS1 or
24.7 ± 4.5°C and 56.1 ± 14.8% for HPS, respectively; during the
second experiment they were 22.8 ± 3.1°C and 61.9 ± 9.9% for
AP673L and NS1 or 23.6 ± 3.8°C and 51.4 ± 9.2% for HPS, respec-
tively. Statistical analysis for comparison of the different light
treatments was done using the Tukey test, with the level of signifi-
cance at 5%, while statistical comparisons between the experi-
ments were performed with one-way analysis of variance (ANO-
VA) in RStudio environment (version 3.3.3, www.rstudio.com).
Results and Discussion
Plant Morphology and Flower Yield
The morphology of the flowering plants after 46 days
of the short-day period differed significantly between the
LED light treatments and the HPS treatment. Plants
0
25
50
75
HPS
aAP673L NS1
***
**
a A b B b B
0
5
10
15
HPS
bAP673L NS1
***
***
***
a A b B b B
0
10
20
40
30
HPS
cAP673L NS1
*
*
a A b A b A
0
10
20
30
HPS
dAP673L NS1
***
*
***
a A b B a B
0
5
10
15
HPS
eAP673L NS1
*
*
b B a A a A
0
0.05
0.10
0.20
0.15
HPS
fAP673L NS1
b B a A a A
0
0.05
0.10
0.20
0.15
HPS
gAP673L NS1
***
***
***
b B a A a B
0
0.2
0.4
0.6
0.8
HPS
hAP673L NS1
***
***
c C b B a A
0
2
4
6
HPS
iAP673L NS1
a A a A a A
Fig. 2. Bar graphs (mean and standard deviation) of plant parameters evaluated. a Height (cm). b Stem (g/plant).
c Flowers (g/plant). d Leaves (g/plant). e THC in flowers (%). f CBD in flowers (%). g THCV in flowers (%).
h CBG in flowers (%). i Yield of cannabinoids (g/plant). Different letters inside the bars show significant differ-
ences (Tukey HSD, p < 0.05). Solid lines and lower case letters are for trial 1, and dashed lines and upper case
letters are for trial 2. Significant differences between trials are represented by asterisks (*p < 0.05, **p < 0.01,
***p < 0.001).
Magagnini/Grassi/Kotiranta
Med Cannabis Cannabinoids 2018;1:19–27
24
DOI: 10.1159/000489030
grown under NS1 and AP673L were shorter and more
compact compared to those grown under the HPS treat-
ment. The plants grown under HPS were significantly
taller and had higher stem dry weight compared to those
grown under the LED light treatments (Fig.2a, b); no sig-
nificant differences were found between the two LED
spectra. Similar results between light treatments were
found in both experiments; however, the differences in
results between experiments were significant. In experi-
ment 1, plant height and dry stem weight ranged from
67.4 cm and 8.2 g/plant in HPS to 58.3 cm and 5.5 g in
AP673L, respectively. In experiment 2, plant height and
dry stem weight ranged from 79.2 cm and 14.2 g in HPS
to 54.5 cm and 7.6 g in AP673L, respectively These results
are consistent with previous studies by Tibbitts et al. [27]
and Wheeler et al. [28], who reported that plants grown
under sole HPS light may suffer from unbalanced mor-
phology expressed by excessive leaf and stem elongation.
This is due to the low R:FR ratio (i.e., the ratio between
red and far-red light) and low blue light emission of the
HPS lamp. The low R:FR ratio increases the activity of
several transcription factors that activate genes involved
in auxin biosynthesis leading to faster stem elongation
[29]. Blue light regulates morphological responses such as
shoot and internode elongation, shoot dry matter, and
leaf area expansion [30]. The flower yield was affected by
the light treatments. HPS plants had higher yields com-
pared to the LED treatments in experiment 1 (Fig.2c). In
the second experiment, the differences between light
treatments in flower yield were not statistically signifi-
cant; however, the same tendency was present (Fig.2c).
The flower yields in the second experiment were 26.6,
23.1, and 22.8 g for HPS, AP673L, and NS1, respectively.
The temperature variation between the two experiments
may have played a role in the case of HPS and NS1 treat-
ments in the yield results. Considering the AP673L treat-
ment, no differences of dry flower weight was observed
between experiments. Yields in the current study are con-
sistent with the recent horticultural studies on cannabis
[22], in which the yield per plant was 20.1 g under similar
lighting conditions to the HPS treatment in this experi-
ment. In experiment 1, the highest leaf dry weight was
measured in treatment NS1, ranging from 21.8 g (NS1) to
16.2 g (AP673L) (Fig.2d). In the second experiment, HPS
had the highest leaf dry weight, while the LED treatments
did not have a significant difference between them. In
experiment 2, the average leaf dry weight ranged from
30.6 g (HPS) to 23.6 g (AP673L). All light treatments
showed significant differences between the two experi-
ments and the experiments did not have a similar trend
between experiments. No differences in flowering time
between treatments were observed during the experi-
ments. This suggests that the fast-growing “G-170” geno-
type is insensitive to changes in the R:FR ratio, a response
commonly seen in long-day plants. No plant pathogens or
nutrient deficiency were found during the experiments.
Cannabinoid Yield
HPS resulted in a significant decline of THC concen-
tration in flowers compared to both LED treatments in
both experiments, while no significant differences be-
tween the two LED types were observed. The amount of
THC (% w/w) was highest in treatment NS1 and lowest
in treatment HPS in both experiments 1 and 2 (Fig.2e).
In experiment 1, HPS had 38% less (9.5%) THC com-
pared to NS1 (15.4%), in experiment 2, the equivalent
number was 26%. One-way ANOVA between the two ex-
periments showed a slight but significant (p < 0.05) dif-
ference in the THC concentration in treatments HPS and
AP673L but not in treatment NS1. The drop in the THC
concentration under HPS led to a corresponding decrease
in CBD, THCV, and especially CBG, which consequently
resulted in a significant increase in the THC proportion
compared to the LED treatments. HPS had a higher pro-
portion of THC in the total cannabinoid content (95.3%
in the first experiment and 96.0% in the second experi-
ment) compared to NS1 (94.3 and 94.9%). Moreover,
comparison between experiments showed a strong differ-
ence in the THC proportion under HPS and a slight but
significant (p < 0.05) difference in NS1, but not in AP673L.
The average CBD concentration showed a similar pattern
to the THC concentration (Fig.2f). The CBD concentra-
tion was highest in the LED treatments and lowest in the
HPS treatment in both experiments. In experiment 1,
HPS had 35% less (0.1%) CBD compared to NS1 (0.2%).
In experiment 2, the equivalent number was 29%. There
were no significant differences in CBD concentrations
between the experiments in any of the light treatments. In
experiment 1, the THCV concentration was significantly
higher in treatments AP673L (0.2%) and NS1 (0.2%)
compared to HPS (0.2%) (Fig.2g). In experiment 2, the
THCV concentrations in all treatments were significant-
ly lower than in experiment 1. AP673L resulted in the
highest concentration of THCV (0.1%), which was 35%
more than in the HPS treatment (0.1%) and 21% more
than in the NS1 treatment (0.1%). In experiment 1, the
average THCV purity showed no significant relationship
between light treatments and ranged from 1.7% under
HPS to 1.2% under NS1. In experiment 2, NS1 treatment
resulted in a lower THCV proportion (0.5%) compared
Light Spectrum and Cannabis sativa L.
25
Med Cannabis Cannabinoids 2018;1:19–27
DOI: 10.1159/000489030
to HPS (0.6%) or AP673L (0.7%) (data not shown). There
was a strong and significant difference in the THCV con-
tent and proportion values between the experiments in all
light treatments. Data obtained from this study indicate
that the light spectrum has an effect on the biosynthesis
of CBG (Fig.2h). The CBG concentration was highest in
the NS1 treatment in both experiments. NS1 had 207 and
107% more CBG compared to the HPS treatment in ex-
periments 1 and 2, respectively, and 63 and 21% more
than AP673L in experiments 1 and 2, respectively. In the
HPS and AP673L treatments, the results differed signifi-
cantly (p < 0.001) between the two experiments. CBG
proportion also showed a similar pattern to CBG content.
The NS1 treatment had the highest CBG purity in both
experiments (3.4 and 3.5%), followed by AP673L (2.6 and
2.9%) and HPS (1.8 and 2.3%). There were significant dif-
ferences in CBG proportion among the experimental tri-
als under the AP673L (p < 0.05) and HPS lamps (p < 0.01),
but not under NS1. There were no significant differences
found in the total yield of cannabinoids between the light
treatments or between the two experiments (Fig.2i). In
experiment 1, the highest cannabinoid yield per plant was
recorded under NS1 (4.3 g/plant) and the lowest under
HPS (3.2 g/plant). In experiment 2, results were following
a similar pattern and the highest cannabinoid yield was in
the NS1 treatment (3.8 g) and the lowest in the HPS treat-
ment (3.3 g).
The first enzyme in the cannabinoid pathway is a type
III PKS, named tetraketide synthase (TKS), which re-
quires the presence of a polyketide cyclase enzyme, named
olivetolic acid cyclase (OAC) to form olivetolic acid (OA)
[31]. OA reacts with geranyl pyrophosphate (GPP) by
GPP:olivetolate geranyltransferase, named CBGA syn-
thase (CBGAS), to form CBGA [32], which is converted
by oxidocyclase enzymes to the major cannabinoids
THCA and CBDA, the biogenic acids of THC and CBD
[33]. Unfortunately, no data are available regarding the
expression regulation of these genes. In higher plants,
the chalcone synthase (CHS) superfamily, a well-studied
plant type III PKS, is substantially light induced, resulting
in a variety of polyphenol scaffold accumulations [34].
Plants have evolved a complex photoreceptor system to
perceive red and far-red (phytochromes), green, blue,
UV-A (cryptochromes, phototropins, ZTL/FKF1/LKP2),
and UV-B light (UVR8) [35]. Photoreceptors activate
various signal transduction cascades to regulate light-de-
pendent responses via transcriptional factors and related
gene expression. For example, shorter wavelengths, in the
range of blue and UV light, are found to be the most ef-
fective in the accumulation of anthocyanins and flavo-
noids, often by increasing the expression of flavonoid
pathway genes or transcription factors [36, 37]. Strawber-
ries treated with blue light showed a significant increase
in anthocyanin content and transcript levels of FaCHS, a
key enzyme in the biosynthesis of flavonoid and antho-
cyanins [38]. In the same study, using overexpression, it
was shown that phototropin (PHOT2) was involved in
blue light-induced anthocyanin accumulation. Also,
cryptochromes (CRY1 and CRY2) control the blue light-
induced anthocyanin accumulation response [39, 40]. In
the present study, the highest CBG and THC concentra-
tions were measured in the NS1 treatment, which had the
highest portion of blue and UV-A wavelengths in the
spectrum compared to the other treatments. Blue and UV
wavelengths have been previously reported to have a pos-
itive effect on the synthesis of many secondary metabo-
lites in multiple species [30]. Mahlberg and Hemphill [23]
studied the effect of light intensity and light quality on
cannabinoid content in plants grown in greenhouse con-
ditions with altered spectra using different colored filters.
They concluded that a higher light intensity increased the
amount of THC, CBC, and CBN. According to their data,
blue and red light positively affected the THC accumula-
tion in leaves, whereas a green or dark environment had
a negative impact compared to the control treatment
(natural light). In the present study, the highest THC con-
tent measured in the flowers was under the NS1 treat-
ment and the lowest was under HPS. We suggest that the
blue and UV-A wavelengths positively affected THC syn-
thesis in treatments NS1 and AP673L, whereas the lack of
blue and UV-A irradiation in the HPS treatment resulted
in a lower amount of THC in flowers. The amount of blue
and UV-A irradiation was highest in the NS1 treatment;
however, the THC level difference between AP673L and
NS1 was not significant. This result could partially be ex-
plained by the high amount of green irradiation in the
NS1 treatment, which can negatively affect the THC syn-
thesis as also shown in the experiment by Mahlberg and
Hemphill [23]. Green light has also been shown to act
antagonistically to other blue light-induced responses,
such as stomatal closure [41] or anthocyanin accumula-
tion [42]. Another possible cause of drop in cannabinoid
concentration under the HPS lamp was the low R:FR ra-
tio. The R:FR ratio is known to play a key role in the shade
avoidance syndrome in plants through the mediation of
phytochromes [43]. In shaded conditions, plant photore-
ceptors activate shade-avoidance responses and reduce
the expression of the jasmonic acid signaling pathway
and other phytochemical biosynthesis, such as soluble
phenolics, anthocyanins, glucosinolates, and terpenoids
Magagnini/Grassi/Kotiranta
Med Cannabis Cannabinoids 2018;1:19–27
26
DOI: 10.1159/000489030
[29]. Our results suggest that manipulation of light qual-
ity during the flowering phase could be a useful tool to
improve the yield of THC and other cannabinoids in can-
nabis cultivation. We suggest that other complex mecha-
nisms mediated by the UV-A and blue wavelengths may
act synergistically to induce CBG accumulation in can-
nabis flowers, CBG being the precursor of other cannabi-
noids.
Conclusion
These two experiments are part of a trial series aimed
to study the effect of light conditions on cannabis growth.
In conclusion, the experiments presented here demon-
strate that the optimal spectrum for a specific photoperiod
scheme may have diverse beneficial effects on cannabis
growth, yield, and cannabinoid profile. Our study shows
that the light environment plays an important role not
only in plant size and stature but also in the accumulation
of cannabinoids. During a long photoperiod, a low R:FR
ratio is preferable to make more developed long cuttings,
while during a short photoperiod a high proportion of
blue irradiation is suitable to improve the medicinal value
of cannabis in terms of cannabinoid content. Manipula-
tion of the spectrum, an advantage of the LED technology,
offers better space utilization to support the heating and
cooling loads of growing buildings. LED lighting strate-
gies may be applied to improve the energy utilization and
carbon footprint of cannabis crop. The mechanisms un-
derlying the effect of UV-A/blue light wavelength on can-
nabinoid pathways require further elucidation.
Acknowledgment
The authors gratefully acknowledge all the staff members in-
volved in the study. This work was supported by fundings from
Valoya Oy.
Disclosure Statement
The authors declare that Valoya has funded the research activ-
ity. Dr. Stiina Kotiranta is employed at Valoya company.
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