rus
Issue #2/2025
M. M. Degtereva, Y. Levin, A. E. Degterev, I. A. Lamkin, S. A. Tarasov
Development of the Cycloadaptive Lighting Mode to Increase the Lactuca sativa L. Yield
Development of the Cycloadaptive Lighting Mode to Increase the Lactuca sativa L. Yield
DOI: 10.22184/1993-7296.FRos.2025.19.2.154.166
In order to increase plant yield and reduce radiation sources energy consumption, we introduce the concept of the cycloadaptive photomode (CAPM), which adapts to the plant development substages (steps), dynamically changes lighting parameters to optimize their growth and development, and promotes increased photosynthetic pigments synthesis. Based on the results of assessing the spectral composition of LED devices effect on the Lactuca sativa L. development, it was determined that the light-emitting device based on the automated change in the spectral composition of radiation and the photosynthetic photon flux depending density on the stage of plant development in accordance with the cycloadaptive lighting mode leads to increase Lactuca sativa L. yield by 2 times, as well as a decrease in the amount of water used to form 1 g of dry matter by 2.5 times compared to natural lighting.
In order to increase plant yield and reduce radiation sources energy consumption, we introduce the concept of the cycloadaptive photomode (CAPM), which adapts to the plant development substages (steps), dynamically changes lighting parameters to optimize their growth and development, and promotes increased photosynthetic pigments synthesis. Based on the results of assessing the spectral composition of LED devices effect on the Lactuca sativa L. development, it was determined that the light-emitting device based on the automated change in the spectral composition of radiation and the photosynthetic photon flux depending density on the stage of plant development in accordance with the cycloadaptive lighting mode leads to increase Lactuca sativa L. yield by 2 times, as well as a decrease in the amount of water used to form 1 g of dry matter by 2.5 times compared to natural lighting.
Теги: crop yield cycloadaptive photomode energy efficiency lactuca sativa l. light-emitting diode photosynthetically active radiation photosynthetic photon flux density spectral characteristic плотность фотосинтетического фотонного потока светодиод спектральная характеристика урожайность фотосинтетически активная радиация циклоадаптивный фоторежим эффективность использования электроэнергии
Development of the Cycloadaptive Lighting Mode to Increase the Lactuca sativa L. Yield
M. M. Degtereva, Y. Levin, A. E. Degterev, I. A. Lamkin, S. A. Tarasov
Saint Petersburg Electrotechnical University "LETI", Saint Petersburg, Russia
In order to increase plant yield and reduce radiation sources energy consumption, we introduce the concept of the cycloadaptive photomode (CAPM), which adapts to the plant development substages (steps), dynamically changes lighting parameters to optimize their growth and development, and promotes increased photosynthetic pigments synthesis. Based on the results of assessing the spectral composition of LED devices effect on the Lactuca sativa L. development, it was determined that the light-emitting device based on the automated change in the spectral composition of radiation and the photosynthetic photon flux depending density on the stage of plant development in accordance with the cycloadaptive lighting mode leads to increase Lactuca sativa L. yield by 2 times, as well as a decrease in the amount of water used to form 1 g of dry matter by 2.5 times compared to natural lighting.
Keywords: light-emitting diode, spectral characteristic, cycloadaptive photomode, photosynthetically active radiation, photosynthetic photon flux density, energy efficiency, crop yield, Lactuca sativa L.
Article received: 07.11.2024
Article accepted: 21.11.2024
Introduction
Light-emitting structures based on semiconductor compounds and their solid solutions are actively used in artificial plant lighting devices due to the ability to generate radiation in the entire visible range, as well as high efficiency and low energy consumption [1]. The role of light spectral quality in satisfying the peculiar manifestations at various stages of plant development (germination, vegetation and flowering) remains insufficient and research [2]. To ensure effective plant development, it is necessary to take into account many parameters, such as germination energy, leaf formation, root and hypocotyl length, leaf area, plant stress level and a number of other factors.
Today, there is dynamic lighting [3–6] that regulates light intensity, wavelength, and photoperiod and is aimed at simulating natural lighting (NL) conditions during the main stages of plant growth (germination, vegetation, and flowering) without taking into account the peculiarities of changes in biometric development parameters. To achieve high plant yields and improve consumer properties, as well as to reduce the radiation sources energy consumption, we propose using the cycloadaptive lighting mode that takes into account the substages of traditional development phases.
Cycloadaptive photomode is a lighting mode that adapts depending on the cycle and substage of plant development and dynamically changes the photosynthetic photon flux density, the wavelengths ratio and the illumination depending duration on the plant development current stage. The term “cycloadaptive” refers to a lighting method adapted to the plant development biological cycles, which improves the growth and plants development at different stages of cultivation, increasing their yield and phytochemical composition. In the light of the rapid development of the agro-industrial complex, there is a need to create LED irradiators with higher efficiency compared to traditional lighting sources in the greenhouse industry to increase the agricultural plants yield [7–10]. The aim of the work is to create the cycloadaptive lighting mode to increase the Lactuca sativa L. yield.
Materials and methods
To assess the plant lighting efficiency at development different stages when creating universal light-emitting devices that are effective for plant growth, we proposed a study of changes in the biometric parameters of agricultural crop development during the vegetation cycle. The Lactuca sativa L. seed germination installation consists of 63 boxes (9 × 9 cm). As the study part of the LED light sources effect on the Lactuca sativa L. variety “Vyuga” growth, 15 experimental light-emitting devices were developed based on 445 nm (b) and 660 nm (r) LEDs with different spectral compositions of radiation (100b, 75b / 25r, 50b / 50r, 25b / 75r, 100r) and photosynthetic photon flux density (PPFD) values of 100, 200 and 300 μmol · m−2 · s−1.
Lactuca sativa L. seeds were planted in Petri dishes on filter paper to retain moisture. The photoperiod in the germination chamber was 14 / 10 hours (day / night) from 8:00 am to 10:00 pm. Seeds watering in the first 10 days of germination was carried out twice a day with 5 ml at a temperature of 15 °C, later it was increased to 15 ml. The temperature was maintained in the range from 19 °C to 21 °C. All experiments were carried out in accordance with the GOST‑12038-84 standard requirements.
A total of 1980 plants were selected for the experiment, of which 22 groups of 30 plants were formed with three replicates and placed under different lighting conditions. Developmental parameters were analyzed separately for each plant. Statistical software was used for all statistical analyses at a significance level of p = 0.05. Data were assessed for normality using the Shapiro-Wilk test and subsequently subjected to one-way analysis of variance (ANOVA) followed by a post hoc Tukey test.
Results and discussion
During the growing, we determined the following experimental samples growth parameters: germination energy, %; cotyledon leaves emergence, %; chlorophyll fluorescence spectra measurement; average root and hypocotyl length, cm; the first and subsequent leaves emergence, %; plant stress; leaf area, cm2; leaf part weight, g; dry matter weight (leaf part), g; yield, kg / m2; transpiration coefficient; chlorophylls a and b, carotenoids content.
Seeds germinated under HPS lighting were used as a control group (three boxes of 30 seeds), since the samples grown under GOST conditions showed low results. After the germination period was complete, the seedlings were transplanted into the soil. The full growth cycle in this study was 35 days.
Based on the study results, the most effective lighting modes of the universal light-emitting device at different Lactuca sativa L. development stages were determined. Based on the data obtained, the cycloadaptive photomode program was developed, which is given in Table.
At step 1 of germination, 50b / 50r lighting mode is actively absorbed by plant photoreceptors. A high PPFD value is not required for activation, otherwise abscisic acid (ABA) is formed, which slows down seed germination. At step 2 of germination, the best growth stimulation was observed under natural sunlight (5.8 times higher than HPS). When moving to the stage of cotyledon leaves active emergence and photosynthetic pigments synthesis, more light is required, otherwise cell elongation and plant extension occur, which leads to the stem high fragility. At step 3 of germination, 100b lighting mode with a high PPFD value leads to the delay in plant extension, which contributes to an increase in leaf area. Increasing the blue light proportion reduces plant growth, but increases the chloroplasts number and the photosynthesis efficiency. At step 1 of vegetation, plants enter the active growth stage, requiring a high PPFD value. The 50b / 50r lighting mode stimulates the chlorophylls and carotenoids synthesis, which leads to an increase in the photosynthesis rate. At step 2 of vegetation, a high PPFD value begins to cause plant stress, which leads to the reactive oxygen species (ROS) formation, which cause lipid peroxidation in cell membranes and lead to a decrease in the photosynthesis activity.
A high proportion of UV, B and G light promotes the econdary metabolites formation, which reduce ROS. Far red (FR) light increases the photosynthetic apparatus size. At step 3 of vegetation, after the ROS formation has decreased, the phytoirradiator is switched to the 50b / 50r lighting mode to reduce energy consumption. At step 4 of vegetation, a decrease in the PPFD value and an increase in the red light 25b / 75r proportion causes the photosynthetic pigments accumulation, which helps to reduce the stress impact and accumulate biomass.
To evaluate the cycloadaptive photomode efficiency, we developed the light-emitting device consisting of three main parts: the light-emitting module, the electronics module containing methods for stimulating the increase in plant yield, and the appliance case. The light-emitting module includes ultraviolet LEDs 370 nm with the spectral line width of 8 nm, defined as the wavelengths difference corresponding to half the maximum radiation intensity of the measured source (Δλ0.5), capable of causing changes in the various plant hormones activity and enzymes, as a result of which the pigment synthesis algorithms and the photosynthesis algorithm change [11]; blue LEDs 445 nm (Δλ0.5 19 nm), designed to initiate chlorophyll synthesis in plants and contribute to an increase in leaf thickness; green LEDs 525 nm (Δλ0.5 35 nm), which have an effect on stimulating photosynthesis in shaded leaves [12]; red LEDs 660 nm (Δλ0.5 20 nm), which promote plants vegetative growth, phytochrome activation, increase in fresh and dry weight, stem elongation and leaf growth in many plant species; far red (FR) LEDs 730 nm (Δλ0.5 36 nm), which in combination with 660 nm LEDs allow for the photomorphogenic effects regulation associated with the phytochromes stimulation [13]. The study of the electrical and spectral-energy LEDs characteristics (Epistar, Taiwan) used in the light-emitting device was conducted (Figure 1).
For efficient light-emitting device operation with CAPM, the photosynthetic photon flux density should be at least 300 μmol · m−2 · s−1. The spectral composition of the radiation and the PPFD level were measured using a Spectral PAR PG200N spectrometer at the 19 cm plant height (Figure 2).
The light-emitting device photosynthetic photon flux was measured using the fast-scanning USB4000-UV-VIS spectrometer (USA) connected via the fiber-optic cable to the AvaSphere integrating sphere (Netherlands), which is a hollow sphere with an inner part coated with fluoroplastic with high reflective and scattering properties [14]. The luminous flux absolute value for calibrating the LED emitters was measured using the LS‑1-CAL-IN reference lamp (USA) with the reliably known luminous efficiency and spectral composition of the radiation, AvaSphere integrating sphere (Netherlands), USB4000-UV-VIS spectrometer (USA), and the P600-2-VIS-NIR optical fiber (USA). The LED current values, voltage, and power readings were also recorded. All measurements were carried out at the stable temperature of 25 °C and the humidity of 70%. The photosynthetic photon flux calculation was carried out according to [15]. The integration limits of 400–700 nm correspond to the photosynthetically active radiation range, where the light has sufficient energy to excite electrons in chlorophyll molecules and other photopigments, which is necessary to initiate photosynthetic reactions, growth and plants development.
FРAR = ϕλ dλ = ϕλ · λ dλ,
where FРAR – the photosynthetic photon flux PPF, μmol · s−1;
λ – the wavelength, nm;
h = 6.623 · 10–34 – the Planck’s constant, J · s;
ϕλ – the radiation power distribution spectral density of the device (in the PAR region), W · nm−1;
NA = 6.022 · 1017 is Avogadro’s number, μmol−1;
c = 3 · 1017 is the light speed, nm · s−1;
K = 8.36 · 10–3 is the coefficient, μmol · nm−1 · J−1.
The developed light-emitting device efficiency was carried out according to [15].
ηPAR = ,
where ηPAR – the efficiency in the PAR region, μmol · J−1;
FPAR – the photosynthetic photon flux PPF, μmol · s−1;
P – the power consumption, W.
The device efficiency in the photosynthetically active radiation region is 2.3 μmol · J−1, which is 28% higher than the efficiency in the PAR region of the traditional greenhouse radiation source – HPS. The device photosynthetic photon flux is 149.4 μmol · s−1 with the 65 W lamp power.
For the developed light-emitting device, we also calculated the illumination uniformity coefficient based on the PPFD value at different distances from the radiation source to the radiation receiver (Figure 3). For the 19 cm distance, the uniformity coefficient was 0.87, for the 40 cm – 0.94, for the 60 cm – 0.96.
The device’s operating programs set the light radiation optimal parameters, spectral composition, PPFD and light period duration for plant photoreceptors effective impact, ensuring optimal development, as well as the best agricultural crops morphology. The use of phytoirradiator with the CAPM reduces energy costs by up to five times compared to the HPS due to the ability to obtain the necessary spatial flow distribution parameters, its intensity and spectral distribution depending on the growth stage and plant species.
The developed light-emitting device with the cycloadaptive lighting mode made it possible to increase the leafy vegetable crop yield of Lactuca sativa L. by 2 times and to reduce the transpiration coefficient by 2.5 times compared to the NL (figure 4). The device also has a higher energy use efficiency, which is the ratio of fresh plant mass yield to the radiation source energy consumption (9 times more efficient than HPS).
In addition to high yields, an important task is to increase the photosynthetic pigments content that affect the photosynthesis rate [16]. The chlorophylls a concentration when using the cycloadaptive lighting mode (figure 5) was the highest and exceeded concentration for the HPS samples by 85%, for the samples grown under natural light by 55%; the concentration of chlorophylls b under CAPM was 64% and 92% higher compared to HPS and NL, respectively; the concentration of carotenoids was also maximum for CAPM (99% and 60% higher than HPS and NL, respectively).
Figure 6 shows that the relationship between the chlorophylls a, b, carotenoids content and plant yield at PPFD of 100 μmol · m−2 · s−1, corresponding to the maximum yield values in the experiment, forms linear dependencies with the determination coefficients R2 = 0.69 (correlation r = 0.833, p < 0.05), R2 = 0.65 (correlation r = 0.805, p < 0.05), R2 = 0.59 (correlation r = 0.768, p < 0.05), respectively. The CAPM use effectively stimulated the photosynthetic pigments biosynthesis, which led to the increase in the Lactuca sativa L. yield.
Conclusion
As a result of the work, we developed the cycloadaptive photomode that increased the Lactuca sativa L. yield by two times, reduced the transpiration coefficient by 2.5 times compared to natural light. Plant stress was reduced by 3.7 times compared to HPS and by 1.5 times compared to natural light. The chlorophyll a, chlorophyll b and carotenoids concentration when using a light-emitting device with the cycloadaptive photomode was increased by 85%, 64% and 99%, respectively, compared to the control group. The developed device has a higher energy use efficiency (9 times more efficient than HPS). The phytoirradiator use reduces energy costs up to five times due to the ability to obtain the required parameters of spatial flow distribution, its intensity and spectral distribution depending on the growth stage and plant species. The developed light-emitting device provides a photosynthetic photon flux density of at least 300 μmol · m−2 · s−1; unlike standard commercial phytolamps for plants, the device efficiency in the photosynthetically active radiation region is 2.3 μmol · J−1, which is 28% higher than the efficiency of a traditional greenhouse radiation source – HPS. The use of effective lighting modes for agricultural crops in agro-industrial enterprises will reduce energy costs of electricity and water supply due to the possibility of obtaining the necessary intensity parameters and spectral distribution depending on the growth stage and type of plant, and will also ensure high yields.
AUTHORS CONTRIBUTION
Degtereva Mariya Mikhailovna – measurement the LEDs parameters in the field of photosynthetically active radiation, experimentation, creating the cycloadaptive lighting mode, data analysis, editing of the article, analysis of literature.
Levin Yevgeniy – measurement of spectral and energy characteristics of LEDs, editing of the article, analysis of literature.
Degterev Alexander Eduardovich – measurement of the electrical characteristics of LEDs, editing the article.
Lamkin Ivan Anatolyevich – scientific work management, work planning, article editing.
Tarasov Sergey Anatolyevich – problem setting and scientific research management.
AUTHORS
Mariya M. Degtereva – assistant professor, department of photonics St. Petersburg Electrotechnical University “LETI”, St. Petersburg, Russia; e-mail: mmromanovich@etu.ru.
ORCID: 0000-0001-6797-0595
Yevgeniy Levin – 2st year postgraduate student of St. Petersburg Electrotechnical University “LETI”, St. Petersburg, Russia; e-mail: e_levin@etu.ru.
ORCID: 0009-0000-3811-487X
Alexander E. Degterev – assistant professor, department of photonics St. Petersburg Electrotechnical University “LETI”, St. Petersburg, Russia; e-mail: aedegterev@etu.ru.
ORCID: 0000-0002-6151-6567
Ivan A. Lamkin – Candidate of Technical Sciences, Associate Professor of the Department of Photonics, St. Petersburg Electrotechnical University “LETI”, St. Petersburg, Russia; e-mail: ialamkin@etu.ru.
ORCID: 0000-0002-3680-7725
Sergey A. Tarasov – Doctor of Technical Sciences, Head of the Department of Photonics, St. Petersburg Electrotechnical University “LETI”, St. Petersburg, Russia; e-mail: satarasov@etu.ru.
ORCID: 0000-0002-6321-0019
M. M. Degtereva, Y. Levin, A. E. Degterev, I. A. Lamkin, S. A. Tarasov
Saint Petersburg Electrotechnical University "LETI", Saint Petersburg, Russia
In order to increase plant yield and reduce radiation sources energy consumption, we introduce the concept of the cycloadaptive photomode (CAPM), which adapts to the plant development substages (steps), dynamically changes lighting parameters to optimize their growth and development, and promotes increased photosynthetic pigments synthesis. Based on the results of assessing the spectral composition of LED devices effect on the Lactuca sativa L. development, it was determined that the light-emitting device based on the automated change in the spectral composition of radiation and the photosynthetic photon flux depending density on the stage of plant development in accordance with the cycloadaptive lighting mode leads to increase Lactuca sativa L. yield by 2 times, as well as a decrease in the amount of water used to form 1 g of dry matter by 2.5 times compared to natural lighting.
Keywords: light-emitting diode, spectral characteristic, cycloadaptive photomode, photosynthetically active radiation, photosynthetic photon flux density, energy efficiency, crop yield, Lactuca sativa L.
Article received: 07.11.2024
Article accepted: 21.11.2024
Introduction
Light-emitting structures based on semiconductor compounds and their solid solutions are actively used in artificial plant lighting devices due to the ability to generate radiation in the entire visible range, as well as high efficiency and low energy consumption [1]. The role of light spectral quality in satisfying the peculiar manifestations at various stages of plant development (germination, vegetation and flowering) remains insufficient and research [2]. To ensure effective plant development, it is necessary to take into account many parameters, such as germination energy, leaf formation, root and hypocotyl length, leaf area, plant stress level and a number of other factors.
Today, there is dynamic lighting [3–6] that regulates light intensity, wavelength, and photoperiod and is aimed at simulating natural lighting (NL) conditions during the main stages of plant growth (germination, vegetation, and flowering) without taking into account the peculiarities of changes in biometric development parameters. To achieve high plant yields and improve consumer properties, as well as to reduce the radiation sources energy consumption, we propose using the cycloadaptive lighting mode that takes into account the substages of traditional development phases.
Cycloadaptive photomode is a lighting mode that adapts depending on the cycle and substage of plant development and dynamically changes the photosynthetic photon flux density, the wavelengths ratio and the illumination depending duration on the plant development current stage. The term “cycloadaptive” refers to a lighting method adapted to the plant development biological cycles, which improves the growth and plants development at different stages of cultivation, increasing their yield and phytochemical composition. In the light of the rapid development of the agro-industrial complex, there is a need to create LED irradiators with higher efficiency compared to traditional lighting sources in the greenhouse industry to increase the agricultural plants yield [7–10]. The aim of the work is to create the cycloadaptive lighting mode to increase the Lactuca sativa L. yield.
Materials and methods
To assess the plant lighting efficiency at development different stages when creating universal light-emitting devices that are effective for plant growth, we proposed a study of changes in the biometric parameters of agricultural crop development during the vegetation cycle. The Lactuca sativa L. seed germination installation consists of 63 boxes (9 × 9 cm). As the study part of the LED light sources effect on the Lactuca sativa L. variety “Vyuga” growth, 15 experimental light-emitting devices were developed based on 445 nm (b) and 660 nm (r) LEDs with different spectral compositions of radiation (100b, 75b / 25r, 50b / 50r, 25b / 75r, 100r) and photosynthetic photon flux density (PPFD) values of 100, 200 and 300 μmol · m−2 · s−1.
Lactuca sativa L. seeds were planted in Petri dishes on filter paper to retain moisture. The photoperiod in the germination chamber was 14 / 10 hours (day / night) from 8:00 am to 10:00 pm. Seeds watering in the first 10 days of germination was carried out twice a day with 5 ml at a temperature of 15 °C, later it was increased to 15 ml. The temperature was maintained in the range from 19 °C to 21 °C. All experiments were carried out in accordance with the GOST‑12038-84 standard requirements.
A total of 1980 plants were selected for the experiment, of which 22 groups of 30 plants were formed with three replicates and placed under different lighting conditions. Developmental parameters were analyzed separately for each plant. Statistical software was used for all statistical analyses at a significance level of p = 0.05. Data were assessed for normality using the Shapiro-Wilk test and subsequently subjected to one-way analysis of variance (ANOVA) followed by a post hoc Tukey test.
Results and discussion
During the growing, we determined the following experimental samples growth parameters: germination energy, %; cotyledon leaves emergence, %; chlorophyll fluorescence spectra measurement; average root and hypocotyl length, cm; the first and subsequent leaves emergence, %; plant stress; leaf area, cm2; leaf part weight, g; dry matter weight (leaf part), g; yield, kg / m2; transpiration coefficient; chlorophylls a and b, carotenoids content.
Seeds germinated under HPS lighting were used as a control group (three boxes of 30 seeds), since the samples grown under GOST conditions showed low results. After the germination period was complete, the seedlings were transplanted into the soil. The full growth cycle in this study was 35 days.
Based on the study results, the most effective lighting modes of the universal light-emitting device at different Lactuca sativa L. development stages were determined. Based on the data obtained, the cycloadaptive photomode program was developed, which is given in Table.
At step 1 of germination, 50b / 50r lighting mode is actively absorbed by plant photoreceptors. A high PPFD value is not required for activation, otherwise abscisic acid (ABA) is formed, which slows down seed germination. At step 2 of germination, the best growth stimulation was observed under natural sunlight (5.8 times higher than HPS). When moving to the stage of cotyledon leaves active emergence and photosynthetic pigments synthesis, more light is required, otherwise cell elongation and plant extension occur, which leads to the stem high fragility. At step 3 of germination, 100b lighting mode with a high PPFD value leads to the delay in plant extension, which contributes to an increase in leaf area. Increasing the blue light proportion reduces plant growth, but increases the chloroplasts number and the photosynthesis efficiency. At step 1 of vegetation, plants enter the active growth stage, requiring a high PPFD value. The 50b / 50r lighting mode stimulates the chlorophylls and carotenoids synthesis, which leads to an increase in the photosynthesis rate. At step 2 of vegetation, a high PPFD value begins to cause plant stress, which leads to the reactive oxygen species (ROS) formation, which cause lipid peroxidation in cell membranes and lead to a decrease in the photosynthesis activity.
A high proportion of UV, B and G light promotes the econdary metabolites formation, which reduce ROS. Far red (FR) light increases the photosynthetic apparatus size. At step 3 of vegetation, after the ROS formation has decreased, the phytoirradiator is switched to the 50b / 50r lighting mode to reduce energy consumption. At step 4 of vegetation, a decrease in the PPFD value and an increase in the red light 25b / 75r proportion causes the photosynthetic pigments accumulation, which helps to reduce the stress impact and accumulate biomass.
To evaluate the cycloadaptive photomode efficiency, we developed the light-emitting device consisting of three main parts: the light-emitting module, the electronics module containing methods for stimulating the increase in plant yield, and the appliance case. The light-emitting module includes ultraviolet LEDs 370 nm with the spectral line width of 8 nm, defined as the wavelengths difference corresponding to half the maximum radiation intensity of the measured source (Δλ0.5), capable of causing changes in the various plant hormones activity and enzymes, as a result of which the pigment synthesis algorithms and the photosynthesis algorithm change [11]; blue LEDs 445 nm (Δλ0.5 19 nm), designed to initiate chlorophyll synthesis in plants and contribute to an increase in leaf thickness; green LEDs 525 nm (Δλ0.5 35 nm), which have an effect on stimulating photosynthesis in shaded leaves [12]; red LEDs 660 nm (Δλ0.5 20 nm), which promote plants vegetative growth, phytochrome activation, increase in fresh and dry weight, stem elongation and leaf growth in many plant species; far red (FR) LEDs 730 nm (Δλ0.5 36 nm), which in combination with 660 nm LEDs allow for the photomorphogenic effects regulation associated with the phytochromes stimulation [13]. The study of the electrical and spectral-energy LEDs characteristics (Epistar, Taiwan) used in the light-emitting device was conducted (Figure 1).
For efficient light-emitting device operation with CAPM, the photosynthetic photon flux density should be at least 300 μmol · m−2 · s−1. The spectral composition of the radiation and the PPFD level were measured using a Spectral PAR PG200N spectrometer at the 19 cm plant height (Figure 2).
The light-emitting device photosynthetic photon flux was measured using the fast-scanning USB4000-UV-VIS spectrometer (USA) connected via the fiber-optic cable to the AvaSphere integrating sphere (Netherlands), which is a hollow sphere with an inner part coated with fluoroplastic with high reflective and scattering properties [14]. The luminous flux absolute value for calibrating the LED emitters was measured using the LS‑1-CAL-IN reference lamp (USA) with the reliably known luminous efficiency and spectral composition of the radiation, AvaSphere integrating sphere (Netherlands), USB4000-UV-VIS spectrometer (USA), and the P600-2-VIS-NIR optical fiber (USA). The LED current values, voltage, and power readings were also recorded. All measurements were carried out at the stable temperature of 25 °C and the humidity of 70%. The photosynthetic photon flux calculation was carried out according to [15]. The integration limits of 400–700 nm correspond to the photosynthetically active radiation range, where the light has sufficient energy to excite electrons in chlorophyll molecules and other photopigments, which is necessary to initiate photosynthetic reactions, growth and plants development.
FРAR = ϕλ dλ = ϕλ · λ dλ,
where FРAR – the photosynthetic photon flux PPF, μmol · s−1;
λ – the wavelength, nm;
h = 6.623 · 10–34 – the Planck’s constant, J · s;
ϕλ – the radiation power distribution spectral density of the device (in the PAR region), W · nm−1;
NA = 6.022 · 1017 is Avogadro’s number, μmol−1;
c = 3 · 1017 is the light speed, nm · s−1;
K = 8.36 · 10–3 is the coefficient, μmol · nm−1 · J−1.
The developed light-emitting device efficiency was carried out according to [15].
ηPAR = ,
where ηPAR – the efficiency in the PAR region, μmol · J−1;
FPAR – the photosynthetic photon flux PPF, μmol · s−1;
P – the power consumption, W.
The device efficiency in the photosynthetically active radiation region is 2.3 μmol · J−1, which is 28% higher than the efficiency in the PAR region of the traditional greenhouse radiation source – HPS. The device photosynthetic photon flux is 149.4 μmol · s−1 with the 65 W lamp power.
For the developed light-emitting device, we also calculated the illumination uniformity coefficient based on the PPFD value at different distances from the radiation source to the radiation receiver (Figure 3). For the 19 cm distance, the uniformity coefficient was 0.87, for the 40 cm – 0.94, for the 60 cm – 0.96.
The device’s operating programs set the light radiation optimal parameters, spectral composition, PPFD and light period duration for plant photoreceptors effective impact, ensuring optimal development, as well as the best agricultural crops morphology. The use of phytoirradiator with the CAPM reduces energy costs by up to five times compared to the HPS due to the ability to obtain the necessary spatial flow distribution parameters, its intensity and spectral distribution depending on the growth stage and plant species.
The developed light-emitting device with the cycloadaptive lighting mode made it possible to increase the leafy vegetable crop yield of Lactuca sativa L. by 2 times and to reduce the transpiration coefficient by 2.5 times compared to the NL (figure 4). The device also has a higher energy use efficiency, which is the ratio of fresh plant mass yield to the radiation source energy consumption (9 times more efficient than HPS).
In addition to high yields, an important task is to increase the photosynthetic pigments content that affect the photosynthesis rate [16]. The chlorophylls a concentration when using the cycloadaptive lighting mode (figure 5) was the highest and exceeded concentration for the HPS samples by 85%, for the samples grown under natural light by 55%; the concentration of chlorophylls b under CAPM was 64% and 92% higher compared to HPS and NL, respectively; the concentration of carotenoids was also maximum for CAPM (99% and 60% higher than HPS and NL, respectively).
Figure 6 shows that the relationship between the chlorophylls a, b, carotenoids content and plant yield at PPFD of 100 μmol · m−2 · s−1, corresponding to the maximum yield values in the experiment, forms linear dependencies with the determination coefficients R2 = 0.69 (correlation r = 0.833, p < 0.05), R2 = 0.65 (correlation r = 0.805, p < 0.05), R2 = 0.59 (correlation r = 0.768, p < 0.05), respectively. The CAPM use effectively stimulated the photosynthetic pigments biosynthesis, which led to the increase in the Lactuca sativa L. yield.
Conclusion
As a result of the work, we developed the cycloadaptive photomode that increased the Lactuca sativa L. yield by two times, reduced the transpiration coefficient by 2.5 times compared to natural light. Plant stress was reduced by 3.7 times compared to HPS and by 1.5 times compared to natural light. The chlorophyll a, chlorophyll b and carotenoids concentration when using a light-emitting device with the cycloadaptive photomode was increased by 85%, 64% and 99%, respectively, compared to the control group. The developed device has a higher energy use efficiency (9 times more efficient than HPS). The phytoirradiator use reduces energy costs up to five times due to the ability to obtain the required parameters of spatial flow distribution, its intensity and spectral distribution depending on the growth stage and plant species. The developed light-emitting device provides a photosynthetic photon flux density of at least 300 μmol · m−2 · s−1; unlike standard commercial phytolamps for plants, the device efficiency in the photosynthetically active radiation region is 2.3 μmol · J−1, which is 28% higher than the efficiency of a traditional greenhouse radiation source – HPS. The use of effective lighting modes for agricultural crops in agro-industrial enterprises will reduce energy costs of electricity and water supply due to the possibility of obtaining the necessary intensity parameters and spectral distribution depending on the growth stage and type of plant, and will also ensure high yields.
AUTHORS CONTRIBUTION
Degtereva Mariya Mikhailovna – measurement the LEDs parameters in the field of photosynthetically active radiation, experimentation, creating the cycloadaptive lighting mode, data analysis, editing of the article, analysis of literature.
Levin Yevgeniy – measurement of spectral and energy characteristics of LEDs, editing of the article, analysis of literature.
Degterev Alexander Eduardovich – measurement of the electrical characteristics of LEDs, editing the article.
Lamkin Ivan Anatolyevich – scientific work management, work planning, article editing.
Tarasov Sergey Anatolyevich – problem setting and scientific research management.
AUTHORS
Mariya M. Degtereva – assistant professor, department of photonics St. Petersburg Electrotechnical University “LETI”, St. Petersburg, Russia; e-mail: mmromanovich@etu.ru.
ORCID: 0000-0001-6797-0595
Yevgeniy Levin – 2st year postgraduate student of St. Petersburg Electrotechnical University “LETI”, St. Petersburg, Russia; e-mail: e_levin@etu.ru.
ORCID: 0009-0000-3811-487X
Alexander E. Degterev – assistant professor, department of photonics St. Petersburg Electrotechnical University “LETI”, St. Petersburg, Russia; e-mail: aedegterev@etu.ru.
ORCID: 0000-0002-6151-6567
Ivan A. Lamkin – Candidate of Technical Sciences, Associate Professor of the Department of Photonics, St. Petersburg Electrotechnical University “LETI”, St. Petersburg, Russia; e-mail: ialamkin@etu.ru.
ORCID: 0000-0002-3680-7725
Sergey A. Tarasov – Doctor of Technical Sciences, Head of the Department of Photonics, St. Petersburg Electrotechnical University “LETI”, St. Petersburg, Russia; e-mail: satarasov@etu.ru.
ORCID: 0000-0002-6321-0019
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