Targeted use of LEDs in improvement of production efficiency through phytochemical enrichment

Effects of Light Intensity on Growth and Quality of Lettuce and Spinach Cultivars in a Plant Factory

The decreased quality of leafy vegetables and tipburn caused by inappropriate light intensity are serious problems faced in plant factories, greatly reducing the economic benefits. The purpose of this study was to comprehensively understand the impact of light intensity on the growth and quality of different crops and to develop precise lighting schemes for specific cultivars. Two lettuce (Lactuca sativa L.) cultivars-Crunchy and Deangelia-and one spinach (Spinacia oleracea L.) cultivar-Shawen-were grown in a plant factory using a light-emitting diode (LED) under intensities of 300, 240, 180, and 120 μmol m-2 s-1, respectively. Cultivation in a solar greenhouse using only natural light (NL) served as the control. The plant height, number of leaves, and leaf width exhibited the highest values under a light intensity of 300 μmol m-2 s-1 for Crunchy. The plant width and leaf length of Deangelia exhibited the smallest values under a light intensity of 300 μmol m-2 s-1. The fresh weight of shoot and root, soluble sugar, soluble protein, and ascorbic acid contents in the three cultivars increased with the increasing light intensity. However, tipburn was observed in Crunchy under 300 μmol m-2 s-1 light intensity, and in Deangelia under both 300 and 240 μmol m-2 s-1 light intensities. Shawen spinach exhibited leaf curling under all four light intensities. The light intensities of 240 and 180 μmol m-2 s-1 were observed to be the most optimum for Crunchy and Deangelia (semi-heading lettuce variety), respectively, which would exhibit relative balance growth and morphogenesis. The lack of healthy leaves in Shawen spinach under all light intensities indicated the need to comprehensively optimize cultivation for Shawen in plant factories to achieve successful cultivation. The results indicated that light intensity is an important factor and should be optimized for specific crop species and cultivars to achieve healthy growth in plant factories.

Modulation of Antioxidant Compounds in Fruits of Citrus reticulata Blanco Using Postharvest LED Irradiation

Phlegrean mandarin fruits are already known for health-promoting properties due to the high concentration of phytochemicals in peel, pulp, and seed. Biotic and abiotic factors, including light, may modulate their biosynthesis, metabolism, and accumulation. In this context, light-emitting diodes (LED) have recently been applied to control nutritional traits, ripening process, senescence, fruit shelf-life, and pathogenic microbial spoilage of fruits. This study investigated the effect of the seven-day exposure of Phlegrean mandarin fruits to two LED regimes, white (W) and red-blue (RB), to test the possibility that the storage under specific light wavelengths may be used as green preservation technology that enhances fruit phytochemical properties. To pursue this aim, the antioxidant activity and polyphenolic profile of the pulp and peel of mandarins under W and RB light regimes were evaluated and compared with Control fruits not exposed to LED treatment. Our results indicated that storage under W and RB treatments modulates the antioxidant content in pulp and peel differently. Compared to W, the RB regime increases the ascorbic acid, flavonoid, anthocyanin, and carotenoid concentrations, while the polyphenol profile analysis reveals that the number of important phytochemicals, i.e., quercetin rutinoside, chlorogenic acid, sinensetin, and rutin, are higher under W. The overall data demonstrated that postharvest LED irradiation is a valid tool for modifying fruit phytochemical properties, which also boosts specific bioactive compounds.

A comparison of consistent UV treatment versus inconsistent UV treatment in horticultural production of lettuce

UV radiation is an underrated radiation currently missing in many horticultural production systems of vegetables in protected cultivation. It can be added e.g., in LED light sources. Using lettuce as a model plant, this study determined whether the use of UVB LEDs is suitable (1) for use in consistent systems (indoor farming) or (2) inconsistent systems (greenhouse). Blue and red LEDs were selected as additional artificial lighting to UVB LEDs. Both approaches led to a reproducible increase of desired flavonol glycosides, such as quercetin-3-O-(6''-O-malonyl)-glucoside or quercetin-3-O-glucuronide and the anthocyanin cyanidin-3-O-(6''-O-malonyl)-glucoside in lettuce. The impact of the consistent UVB treatment is higher with up to tenfold changes than that of the inconsistent UVB treatment in the greenhouse. Varying natural light and temperature conditions in greenhouses might affect the efficiency of the artificial UVB treatment. Here, UVB LEDs have been tested and can be recommended for further development of lighting systems in indoor farming and greenhouse approaches.

High production of flavonols and anthocyanins in Eruca sativa (Mill) Thell plants at high artificial LED light intensities

Eruca sativa (arugula) is a food crop containing valuable bioactive flavonoids. Plants growing with monochrome light-emitting diodes (LED) and "binary" light sources, including red/blue (RB), were tested using HPLC-DAD-ESI-MS/MS. Most artificial lighting options with a high intensity of 1000 μmol m^-2s^-1 (except for warm white light) resulted in an almost 20-fold increase in flavonol productivity. Monochromatic sources had no advantage over white light in terms of increasing anthocyanin productivity. However, RB light increased the anthocyanin content and productivity of E. sativa plants by more than ten times compared to white light. Plant growth on monochromatic and binary sources at high intensities was comparable to that on white light. Measurement of the content of chlorophyll and its degradation product, phyllobilins, showed that plants are not under stressful conditions. Overall, our data show that a significant increase in flavonoid content can be achieved without a loss of arugula plant biomass.

The Impact of Light Wavelength and Darkness on Metabolite Profiling of Korean Ginseng: Evaluating Its Anti-Cancer Potential against MCF-7 and BV-2 Cell Lines

Korean ginseng is a source of functional foods and medicines; however, its productivity is hindered by abiotic stress factors, such as light. This study investigated the impacts of darkness and different light wavelengths on the metabolomics and anti-cancer activity of ginseng extracts. Hydroponically-grown Korean ginseng was shifted to a light-emitting diodes (LEDs) chamber for blue-LED and darkness treatments, while white fluorescent (FL) light treatment was the control. MCF-7 breast cancer and lipopolysaccharide (LPS)-induced BV-2 microglial cells were used to determine chemo-preventive and neuroprotective potential. Overall, 53 significant primary metabolites were detected in the treated samples. The levels of ginsenosides Rb1, Rb2, Rc, Rd, and Re, as well as organic and amino acids, were significantly higher in the dark treatment, followed by blue-LED treatment and the FL control. The dark-treated ginseng extract significantly induced apoptotic signaling in MCF-7 cells and dose-dependently inhibited the NF-κB and MAP kinase pathways in LPS-induced BV-2 cells. Short-term dark treatment increased the content of Rd, Rc, Rb1, Rb2, and Re ginsenosides in ginseng extracts, which promoted apoptosis of MCF-7 cells and inhibition of the MAP kinase pathway in BV-2 microglial cells. These results indicate that the dark treatment might be effective in improving the pharmacological potential of ginseng.

Phototreatment (below 1100 nm) improving quality attributes of fresh-cut fruits and vegetables: A review

The emerging area of phototreatment technology has shown a significant potential to enhance the quality of fresh-cut fruit and vegetable products (FFVP). This review critically evaluates relevant literatures to address the potential for phototreatment technology (Red, blue, green, ultraviolet and pulsed light) applied to FFVP, outline the key to the success of phototreatment processing, and discuss the corresponding problems for phototreatment processing along with research and development needs. Base on photothermal, photophysical and photochemical process, phototreatment displays a great potential to maintain quality attributes of FFVP. The operating parameters of light, the surface properties and matrix components of the targeted material and the equipment design affect the quality of the fresh-cut products. To adapt current phototreatment technology to industrial FFVP processing, it is necessary to offset some limitations, especially control of harmful substances (For example, nitrite and furan) produced by phototreatment, comparison between different phototreatment technologies, and establishment of mathematical models/databases.

Development of a fuzzy logic-controlled system for home cultivation of sweet basil

As environmental pollution and the global population increase, and the COVID-19 pandemic becomes more severe, demands for indoor farming, especially home food gardening, have also increased. However, most research thus far has focused on large-scale food production, with very few studies having been conducted at the household scale. Also, the devices cultivating household crops with control systems in a continuous way, which minimize fluctuations of environmental conditions, have been rarely developed. Therefore, this study aimed to design a household cultivation system for sweet basil that is automatically and continuously controlled by fuzzy logic with a Raspberry Pi4. Three inputs (temperature, humidity, and growth stage) and seven outputs (fan, humidifier, heater 1, heater 2, LED red, green, and blue) were used with six rules, ensuring that three lights operated independently upon three growth stages. Simulation and actual operation were carried out, resulting in an appropriately controlled system that operated with few defects. In the case of an operation of the input variable, temperature and humidity were maintained at an average of 21.24 °C and 75.58%, respectively, and the LED operation for the growth stage was confirmed to be flawless. For verification of the designed fuzzy system, a comparison between the simulation and actual operation was performed to examine differences and identify problems. To this end, Pearson's correlation coefficients were used, and the direction of correction of the fuzzy logic system was proposed. Through these results, the feasibility of a home cultivation system using fuzzy logic was demonstrated, and it is expected that further studies applying it will be conducted in the future.

Alteration in Light Spectra Causes Opposite Responses in Volatile Phenylpropanoids and Terpenoids Compared with Phenolic Acids in Sweet Basil (Ocimum basilicum) Leaves

Basil (Ocimum basilicum, cv. Dolly) grew under three different light spectra (A, B, and C) created by light-emitting diode lamps. The proportions of UV-A, blue, and green-yellow wavelengths decreased linearly from A to C, and the proportions of red and far-red wavelengths increased from A to C. Photosynthetic photon flux density was 300 μmol m^-2 s^-1 in all spectra. The spectrum C plants had highest concentrations of phenolic acids (main compounds: rosmarinic acid and cichoric acid), lowest concentrations and emissions of phenylpropanoid eugenol and terpenoids (main compounds: linalool and 1,8-cineole), highest dry weight, and lowest water content. Conversely, spectra A and B caused higher terpenoid and eugenol concentrations and emissions and lower concentrations of phenolic acids. High density of peltate glandular trichomes explained high terpenoid and eugenol concentrations and emissions. Basil growth and secondary compounds affecting aroma and taste can be modified by altering light spectra; however, increasing terpenoids and phenylpropanoids decreases phenolic acids and growth and vice versa.

Supplemental light application can improve the growth and development of strawberry plants under salinity and alkalinity stress conditions

The use of complementary light spectra is a potential new approach to studying the increase in plant resilience under stress conditions. The purpose of this experiment was to investigate the effect of different spectra of complementary light on the growth and development of strawberry plants under salinity and alkalinity stress conditions. Plants were grown in the greenhouse under ambient light and irradiated with blue (460 nm), red (660 nm), blue/red (1:3), and white/yellow (400–700 nm) light during the developmental stages. The stress treatments were as follows: control (non-stress), alkalinity (40 mM NaHCO₃), and salinity (80 mM NaCl). Our results showed that salinity and alkalinity stress decreased fresh and dry weights and the number of green leaves, and increased chlorotic, tip burn, and dry leaves. The blue and red spectra had a greater effect on reducing the effects of stress compared to other spectra. Stress conditions decreased SPAD and RWC, although blue light increased SPAD, and blue/red light increased RWC under stress conditions. Blue/red and white/yellow light had the greatest effect on reproductive traits. Stress conditions affected fruit color indicators, and red and blue light had the most significant effect on these traits. Under stress conditions, sodium uptake increased, while K, Ca, Mg, and Fe uptake decreased, markedly. Blue and red light and their combination alleviated this reducing effect of stress. It can be concluded that the effects of salinity and alkalinity stresses can be reduced by manipulating the supplemental light spectrum. The use of artificial light can be extended to stresses.

Cold Stress Resistance of Tomato (Solanum lycopersicum) Seedlings Is Enhanced by Light Supplementation From Underneath the Canopy

Adverse environmental conditions, such as low temperature (LT), greatly limit the growth and production of tomato. Recently, light-emitting diodes (LEDs) with specific spectra have been increasingly used in horticultural production facilities. The chosen spectrum can affect plant growth, development, and resistance, but the physiological regulatory mechanisms are largely unknown. In this study, we investigated the effects of LED light supplementation (W:B = 2:1, light intensity of 100 μmol⋅m-2⋅s-1, for 4 h/day from 9:00 to 13:00) from above and below the canopy on tomato resistance under sub-LT stress (15/8°C). The results showed that supplemental lighting from underneath the canopy (USL) promoted the growth of tomato seedlings, as the plant height, stem diameter, root activity, and plant biomass were significantly higher than those under LT. The activity of the photochemical reaction center was enhanced because of the increase in the maximal photochemical efficiency (F v /F m ) and photochemical quenching (qP), which distributed more photosynthetic energy to the photochemical reactions and promoted photosynthetic performance [the maximum net photosynthetic rate (Pmax) was improved]. USL also advanced the degree of stomatal opening, thus facilitating carbon assimilation under LT. Additionally, the relative conductivity (RC) and malondialdehyde (MDA) content were decreased, while the soluble protein content and superoxide dismutase (SOD) activity were increased with the application of USL under LT, thereby causing a reduction in membrane lipid peroxidation and alleviation of stress damage. These results suggest that light supplementation from underneath the canopy improves the cold resistance of tomato seedlings mainly by alleviating the degree of photoinhibition on photosystems, improving the activity of the photochemical reaction center, and enhancing the activities of antioxidant enzymes, thereby promoting the growth and stress resistance of tomato plants.

Application of light emitting diodes (LEDs) for food preservation, post-harvest losses and production of bioactive compounds: a review

Light-emitting diode (LED) technology is a new non-thermal food preservation method that works by converting light energy into heat. LED has potential to revolutionize crop production, protection and preservation. This technology is economical and environmentally friendly. LEDs have been shown to improve the nutritive quality and shelf life of foods, control the ripening of fruits, induce the synthesis of bioactive compounds and antioxidants and reduce the microbial contamination. This technology also has great scope in countries, where safety, hygiene, storage and distribution of foods are serious issues. While comparing this technology with other lighting technologies, LEDs can bring numerous advantages to food supply chain from farm to fork. In case of small growing amenities which exploit only LEDs, energy expenditure has been successfully reduced while producing nutritious food. LEDs can be used to give us better understanding and control over production and preservation of food with relation to spectral composition of light. LEDs also play significant role in food safety by inactivating the food borne pathogens. Therefore, LED lighting is a very effective and promising technology for extending shelf life of agricultural produce by increasing disease resistance and with increased nutritional values.

Graphical abstract

Light-emitting diodes (below 700 nm): Improving the preservation of fresh foods during postharvest handling, storage, and transportation

In order to maintain the original taste, flavors, and appearance, fresh foods usually do not go through complex processing prior to sale; this makes them prone to deterioration due to external factors. Light-emitting diodes (LEDs) have many unique advantages over traditional preservation technologies leading to their increasing application in the food industry. This paper reviews the luminescence principles of LED, the advantages of LED compared with traditional lighting equipment, and its possible preservation mechanism, and then critically summarizes the beneficial effects of LED irradiation on the ripening and aging process of various fruits and vegetables (climacteric and non-climacteric). The activity changes of many enzymes closely related to crop development and quality maintenance, and the variation of flavor components caused by LED irradiation are discussed. LED illumination with a specific spectrum also has the important effect of maintaining the original color and flavor of meat, seafood, and dairy products. For microorganisms attached to the surface of animal-derived food, both 400-460 nm LED irradiation based on photodynamic inactivation principle and UV-LED irradiation based on ultraviolet sterilization principle have high bactericidal efficacy. Although there is still a lack of useful standards for matching optimal LED irradiation dose with wavelength, perhaps in the near future, the improved LED irradiation system will be applied extensively in the food industry.

Light emitting diodes optimisation for secondary metabolites production by Droseraceae plants

The most abundant active compound in Droseraceae is plumbagin, a naphthoquinone widely used for medical purposes due to its antimicrobial, antitussive, antimalarial and anticancer properties. In this work, we created a light-emitting diode (LED) based culture illumination setup as an alternative to fluorescent lamps traditionally used as a light source in plant in vitro cultures. The plants of Drosera binata and Drosera peltata cultured under LED illumination grew equally well and produced similar amounts of biologically active compounds as plants grown under fluorescent lamps. The plants were cultured on two media differing in mineral composition, sucrose content and pH. Secondary metabolites were extracted with ethanol from the plants after harvesting. The extracts were subjected to HPLC and microbiological analyses. We observed differences in morphology and secondary metabolism between plants of the same species grown on different media. However, we did not note significant changes in secondary metabolite yield under assessed lighting conditions. We propose LEDs as a more efficient, eco-friendly and economically reasonable source of light for big scale in vitro production of plumbagin in Drosera species than fluorescent lamps.

The Interplay between Light Quality and Biostimulant Application Affects the Antioxidant Capacity and Photosynthetic Traits of Soybean (Glycine max L. Merrill)

This paper evaluates the combined effect of biostimulant and light quality on bioactive compound production and seedling growth of soybean (Glycine max L. Merrill) plants. Germinated seeds pre-treated with different concentrations (0.01%, 0.05%, 0.5%) of an amino acid-based biostimulant were grown for 4 days at the dark (D), white fluorescent light (FL), full-spectrum LED (FS), and red-blue (RB) light. Potential changes in the antioxidant content of sprouts were evaluated. Part of the sprouts was left to grow at FL, FS, and RB light regimes for 24 days to assess modifications in plants' anatomical and physiological traits during the early developmental plant stage. The seed pre-treatment with all biostimulant concentrations significantly increased sprout antioxidant compounds, sugar, and protein content compared to the control (seeds treated with H₂O). The positive effect on bioactive compounds was improved under FS and RB compared to D and FL light regimes. At the seedling stage, 0.05% was the only concentration of biostimulant effective in increasing the specific leaf area (SLA) and photosynthetic efficiency. Compared to FL, the growth under FS and RB light regimes significantly enhanced the beneficial effect of 0.05% on SLA and photosynthesis. This concentration led to leaf thickness increase and shoot/root ratio reduction. Our findings demonstrated that seed pre-treatment with proper biostimulant concentration in combination with specific light regimes during plant development may represent a useful means to modify the bioactive compound amount and leaf structural and photosynthetic traits.

Blue:Red LED Light Proportion Affects Vegetative Parameters, Pigment Content, and Oxidative Status of Einkorn (Triticum monococcum L. ssp. monococcum) Wheatgrass

This work aimed to study the effect of some light spectra on the growth, oxidative state, and stress of einkorn wheatgrass (Triticum monococcum L. ssp. monococcum). To this end, six light treatments, having the same total incident photon flux density (PFD) of 200 μmol m^-2 s^-1, were applied to einkorn and compared: only blue light; only red; three blue:red combinations, at different proportions of total PFD (75:25%, 50:50%, and 25:75%, respectively); and a wide spectrum, taken as a control treatment, composed of blue (18% of PFD), red (18%), and intermediate wavelengths (64%). Light treatments affected the contents of pigments (chlorophylls and carotenes), hydrogen peroxide (H₂O₂), and malondialdehyde (MDA). These results revealed the changes in the oxidative status of wheatgrass, in response to the different light treatments. However, the dichromatic light with blue ≥50% of the total PFD appeared to be the best combination, guarantying good wheatgrass yield, increasing pigment content, and reducing H₂O₂ and MDA when compared to the other light treatments. Our findings also contribute to explaining the available literature on the effect of these kinds of light on the increase in phenolic compounds and antioxidant activity in einkorn wheatgrass.

Optimization of Artificial Light for Spinach Growth in Plant Factory Based on Orthogonal Test

Artificial LED source provides the possibility to regulate the lighting environment in plant factorys that use limited space to plant, aiming at high throughput and good quality. However, different parameters of light intensity, quality, and photoperiod will influence the growth and accumulation of bio-compounds in plants. In order to find the optimal setting of LED light for spinach planting, four group experiments were designed using the orthogonal testing method. According to the experimental results, for growth indexes including fresh weight, dry weight, root length and so on, photoperiod is the most influential factor, light intensity is the second, and light quality is the least. The best light mode (R:B = 4:1, photosynthetic photon flux density (PPFD) = 100 μmol∙m⁻²∙s⁻¹ and 13/11 h) among all eight possible combinations in the range was also determined. Furthermore, for quality indexes, including the soluble sugar content, protein content and so on, a new scoring method was introduced to make a comprehensive score for evaluating. Then, the light combination (R:B = 4:1, PPFD = 150 μmol∙m⁻²∙s⁻¹ and 9/15 h) in the range was found as the optimal scheme for spinach quality under those parameters. As there is trade-off between the optimal light parameters for growth and quality, it is necessary to achieve a balance between yield and quality of the plant during production. If farmers want to harvest spinach with larger leaf area and higher yield, they need to pay attention to the adjustment of the photoperiod and use a lower light intensity and a longer lighting time. If they do not mind the yield of the vegetable but want to improve the taste and nutrition of spinach products, they should pay more attention to the light intensity and use a higher light intensity and a shorter lighting time.

Lighting intensity and photoperiod serves tailoring nitrate assimilation indices in red and green baby leaf lettuce

BACKGROUND

Understanding plant responses to light quantity in indoor horticultural systems is important for optimising lettuce growth and metabolism as well as energy utilisation efficiency. Light intensity and photoperiod sufficient for normal plant growth parameters might be not efficient for nitrate assimilation. Therefore, this study explored and compared the effects of different light intensities (100-500 μmol m-2 s-1 ) and photoperiods (12-24 h) on the growth and nitrate assimilation in red and green leaf lettuce (Lactuca sativa L.).

RESULTS

For efficient nitrate assimilation, 300-400 μmol m-2 s-1 photosynthetic photon flux density (PPFD) and 16-18 h photoperiod is necessary for red and green lettuces. The insufficient light quantity resulted in reduced growth and remarkable increase in nitrate and nitrite contents in both cultivars. Short photoperiods, similarly to low PPFD, growth parameters, chlorophyll indices and nitrate assimilation indices showed the shortage of photosynthetic products for normal plant physiological processes. Short photoperiods had the least pronounced effect on nitrate and nitrite contents in lettuce leaves.

CONCLUSION

Light intensity was superior compared to photoperiods for efficient nitrate assimilation in both lettuce cultivars. Under short photoperiods, similarly to low intensity, growth parameters, chlorophyll index and nitrate assimilation indices showed a shortage of photosynthetic products for normal physiological processes. The free amino acid concentration increased, but it was not efficiently incorporated in proteins, as their level in lettuce was lower compared to those for moderate photoperiods. © 2019 Society of Chemical Industry.

Different Postharvest Responses of Fresh-Cut Sweet Peppers Related to Quality and Antioxidant and Phenylalanine Ammonia Lyase Activities during Exposure to Light-Emitting Diode Treatments

The influence of emitting diode (LED) treatments for 8 h per day on functional quality of three types of fresh-cut sweet peppers (yellow, red, and green) were investigated after 3, 7, 11, and 14 days postharvest storage on the market shelf at 7 °C. Red LED light (660 nm, 150 μmol m⁻² s⁻¹) reduced weight loss to commercially acceptable level levels (≤2.0%) in fresh-cuts of yellow and green sweet peppers at 7 and 11 d, respectively. Blue LED light (450 nm, 100 μmol m⁻² s⁻¹) maintained weight loss acceptable for marketing in red fresh-cut sweet peppers up to 11 d. Highest marketability with minimum changes in color difference (∆E) and functional compounds (total phenols, ascorbic acid content, and antioxidant activity) were obtained in yellow and green sweet pepper fresh-cuts exposed to red LED light up to 7 and 11 d, respectively, and for red sweet pepper fresh-cuts exposed to blue LED light for 11 d. Red LED light maintained the highest concentrations of β carotene, chlorophyll, and lycopene in yellow, green, and red sweet pepper fresh-cuts up to 7 d. Similarly, blue LED light showed the highest increase in lycopene concentrations for red sweet pepper fresh-cuts up to 7 d. Red LED (yellow and green sweet peppers) and blue LED (red sweet pepper) lights maintained phenolic compounds by increasing phenylalanine ammonia lyase activity. Thus, the results indicate a new approach to improve functional compounds of different types of fresh-cut sweet pepper.

Modelling Environmental Burdens of Indoor-Grown Vegetables and Herbs as Affected by Red and Blue LED Lighting

Notwithstanding that indoor farming is claimed to reduce the environmental pressures of food systems, electricity needs are elevated and mainly associated with lighting. To date, however, no studies have quantified the environmental and economic profile of Light Emitting Diodes (LED) lighting in indoor farming systems. The goal of this study is to quantify the effect of varying the red (R) and blue (B) LED spectral components (RB ratios of 0.5, 1, 2, 3 and 4) on the eco-efficiency of indoor production of lettuce, chicory, rocket and sweet basil from a life cycle perspective. The functional unit of the assessment was 1 kg of harvested fresh plant edible product, and the International Reference Life Cycle Data System (ILCD) method was employed for impact assessment. Even though most of the materials of the LED lamp and electronic elements were imported from long distances (14,400 km), electricity consumption was the largest contributor to the environmental impacts (with the LED lamps being the main electricity consumers, approximately 70%), apart from the resources use indicator, where the materials of the lamps and the mineral nutrients were also relevant. RB0.5 was the most energy-efficient light treatment but had the lowest eco-efficiency scores due to the lower crop yields.

The growth and development of cress (Lepidium sativum) affected by blue and red light

Today, the use of light emitting diodes (LEDs) are rapidly increasing in horticulture industry as a result of technological advancements. Lighting systems play an important role in the commercial greenhouse productions. As an artificial source of light, LED lamps can contribute to the better and faster growth of horticulture products such as vegetables grown in greenhouses. In this study, the effects of red and blue light spectrums were implemented and performed as a pot experiment under the cultivation-without-soil condition in greenhouse based on a completely random plan with 3 lighting treatments including natural light (control), 60% red light +40% blue light (60R:40B), and 90% red light +10% blue light (90R:10B), repeated 3 times. The results showed that the application of blue and red lights affected the fresh and dry weights of cress as well as its biomass, demonstrating a considerable increase compared to the plants grown under natural sunlight condition. In this regard, the fresh weight of the plant under the 60R:40B treatment had 57.11% increase compared to the natural light treatment. Compared to the control sample, the dry weight had 26.06% increase under 90R:10B treatment. The highest extent of biomass was observed under the 60R:40B lighting treatment with a value of 1.51 (g per kg dry weight of the plant), which was a 68.87% increase compared to the natural light treatment. Under the 60R:40B treatment, cress had its highest length at 19.76 cm. Under the similar treatment, the cress leaf had a total area of 56.78 cm² which was the largest. The stem diameter and the number of leaves under the 60R:40B treatment had their highest values at 3.28 mm and 8.16, respectively. Accordingly, a growing trend was observed with 56.7 and 61.27% increase compared to the control treatment. Furthermore, the biochemical traits of cress, the amount of a, b and total chlorophyll, the amount of anthocyanin and phenolic contents under the application of red and blue light were at their highest values compared to the control treatment. The highest amount of chlorophyll was observed under 60R:40B treatment as 15.09 mg g⁻¹ FW leaf. Moreover, the phenolic contents and the amount of anthocyanin were of significant difference at 1% level of likelihood compared to the control treatment. Therefore, the vegetative growth of cress was substantially affected by red and blue lights, resulting in the enhancement of the plant's biochemical features compared to control condition via adjusting the lighting quality and impacts of each red and blue light spectrum on their specific receptors. As a result, the presence of both lighting spectrums is essential for expanding and increasing the quality of the plant. At the large scale, this technology is capable of improving the commercial greenhouse production performance while helping farmers achieve maximum products. This particular combination of lights is one of the beneficial features of LED lighting systems intended for different types of commercial greenhouse productions, especially the valuable greenhouse products.