Spectra Of Light-emitting Diodes Research Articles

Spectral Design of Light-Emitting Diodes for Plant Photosynthesis Based on Quantum Dots

Light is one of the five indispensable factors for plant growth. Green houses and plant factories have advantages of growing vegetables off-season and high production. However, artificial lighting occupies most of the running cost during the operation of plant factories, and intelligent and programmable light-emitting diodes (LEDs) have been considered to be used as growing lamps to save energy. Taking both the photosynthetic and the visual performances into consideration, luminescent spectrum of LEDs based on quantum dot (QD) materials is designed and optimized according to the photosynthetic action spectrum (PAS) of plants. In our calculation, the three-band QD-based LEDs (QLEDs) show a highest photosynthetic action factor (PAF) of 8.088 and a highest induced photosynthetic index (IPI) of 4.012. The four-band QLEDs show a highest PAF of 7.689 and a highest IPI of 3.818. CdZnS/ZnS and CdZnS/ZnSe QDs are also synthesized for fabricating three- and four-band QLEDs. Investigations of the photosynthetic and the vison performances on these devices are consistent with those theoretical simulation results. Both the simulation and the experimental results show that either the three- or the four-band QLEDs has better photosynthetic parameters than those of the conventional light sources. The fabricated four-band QLED under different applied current exhibits a highest PAF of 2.6942 and a highest IPI of 1.3621. For the vison performances, the four-band device demonstrate a highest CRI of 93 and a highest CCT of 2053 K. Despite the visual performances of the four-band QLEDs show improvement than those of the three-band ones, they still need to be improved to offer better visual experience for human eyes. With further investigation on the synthesis of emission tunable QD materials and the optimization of the spectrum, highly efficient QLEDs with both good photosynthetic and visual performances are expected to be applied in the field of growing lamps.

Measuring the Temperature Shift of the Emission Spectrum of LEDs while Turning Them on with a CMOS Photo Receiving Matrix

The dynamics of the temperature transformation of the emission spectrum of light-emitting diodes using the “running” gate mode of the photodetecting complementary metal oxide semiconductor (CMOS) matrix were investigated. A device has been developed for measuring the parameters of the spectrum shift of LEDs when they are switched on. The device is based on the optical system of the SF-46 spectrophotometer without an exit slit and with a focusing system in front of an SCMOS-00350KPA CMOS photodetector array with a 480 × 640 pixel photosensitive area and 84 μs line-by-line recording time. In terms of speed and wavelength resolution (0.125 nm), the device significantly surpasses the domestic and foreign IS3000-LED, Cary 100/300, Ocean Optic USB2000, etc., spectrometers. The time dependences of the spectrum shift of the red SMD-LED FYLS-3528BURC in the first 40 ms after switching it on at different values of the operating current were obtained experimentally. The obtained dependences can be used to evaluate the thermal parameters of LEDs.

In vitro potato plantlet development under different polychromatic LED spectra and dynamic illumination

We studied growth of potato plantlets of two cultivars under different constant polychromatic light-emitting diodes (LEDs) and dynamic lighting with the spectrum modifications during growth. Light sources constructed by us were sunbox SB, red-green-blue RGB, and full spectrum FS, red-blue. White luminescent lamps were used as control light. Dynamic lighting was achieved by transferring groups of plantlets from one box to another. Red/green/blue portions in the light sources were (in percents): 39R/39G/22B for SB, 63R/21G/16B for RGB, 74R/8G/18B for FS, and 22R/49G/29B for control. PPFD was set at 45 μmol/m2 s. Morphometric measurements were made 14 and 28 days after planting. Plantlets developed differently from initial stages. Cultivar 'Red Scarlett' appeared to be more susceptible to different lighting than 'Innovator'. Light variations RGB and RGB-SB were the most favorable for plantlet development. This is the first report on the dynamic lighting application for growing potato plantlets.

Improvement of Growth and Morphology of Vegetable Seedlings with Supplemental Far-Red Enriched LED Lights in a Plant Factory

Although light-emitting diode (LED) lamps have been broadly applied in horticultural production to improve plant yield and quality, compared to natural light there is a disadvantage in the lack of far-red light in the LED spectrum. Far-red light has been studied widely to control plant growth and development. Therefore, this study aimed to find the effect of supplemental far-red-enriched LED lights to control the growth of tomato, red pepper, cucumber, gourd, watermelon and bottle gourd seedlings. The treatments were cool white LED:far-red LED at ratios of 5:0, 5:1, 5:2 and 5:3. The growth of tomato and red pepper seedlings, including hypocotyl length, was correlated to far-red light and light intensity. The phytochrome photostationary state (PSS) value of maximum hypocotyl length by supplemental far-red-enriched light ranged from 0.69 to 0.77 in tomato and red pepper seedlings. Although hypocotyl lengths of cucumber and watermelon were greatly affected by PSS, the PSS value for maximum hypocotyl length was lower than for tomato and red pepper. These results show that manipulating supplemental far-red enrichment can be used to control vegetable seedling growth with some variation among plant species.

Enhanced light extraction of light-emitting diodes with micro patterns by femtosecond laser micromachining for visible light communication.

A significant enhancement of light extraction of light-emitting diodes (LEDs) with micro patterns has been experimentally investigated. The micro patterns on the surface of a polymer layer are fabricated by a femtosecond laser Bessel beam for obtaining microhole arrays with large depth, resulting in the reduction of photon loss by total internal reflection (TIR) at the surface of the LED. The light output power of the LED is apparently increased by introducing the array patterns without influencing its current-voltage (I-V) characteristics. Moreover, the electroluminescence spectra of a multi-color LED and its angular radiation profiles with orthogonal and hexagonal patterns also have been explored. In addition, the optical field distributions of the micro patterns simulated by the finite difference time domain method have expressed the modulation effect of the array depth. Finally, the patterned LED as a transmitter is embedded in the visible light communication system for evaluating the transmission signal quality.

Influence of light on biomass and lipid production in microalgae cultivation

Microalgae have a diverse application in food, pharmaceutical, beauty, animal feed and bioenergy industry. The demand for high-quality pure microalgae biomass has steered the large-scale production of microalgae in the photobioreactor. The usage of light-emitting diodes (LEDs) as a light source is gaining attention as to conventional fluorescent lamps due to the higher energy conversion ratio, lower heat dissipation and its flexible application in photobioreactors. Besides, the narrow spectrum of LEDs could efficiently promote specific compounds in microalgae. This article reviews the influence of using various LED spectra on the biomass and lipid composition of microalgae. In addition, suggestions on the use of different LEDs cultivating common microalgae species in aquaculture are provided.

Influence of light spectra on the performance of juvenile turbot (Scophthalmus maximus)

Appropriate light conditions in aquaculture systems are essential for fish welfare. Light spectrum, as one of the main characteristics of light, has a significant influence on the performance of teleosts. The development of light emitting diode (LED) technology allows for the precise regulation of light spectrum. This study examined the influence of five different LED spectra, red, orange, green, blue and full spectrum (white) on the performance of juvenile Scophthalmus maximus (seven months post hatching), by analyzing specific growth rate (SGR), feed conversion ratio (FCR), serum glucose and lactate contents, hepatic glycogen contents, antioxidative activity and pathogen resistance. A statistically higher SGR was observed in the blue group compared with the red, orange and white groups. Juveniles exposed to blue spectrum exhibited the lowest FCR. Juveniles exposed to red and orange light exhibited increased hepatic hsp70 mRNA levels, as well as increased mRNA expression levels of copper/zinc superoxide dismutase (cu/zn-sod), manganese superoxide dismutase (mn-sod), catalase (cat), glutathione peroxidase (gsh-px) and lysozyme (lzm). However, hepatic and serum total superoxide dismutase (T-sod), Cat and Gsh-px activities were not significantly higher in the red and orange groups. Hepatic Lzm activity was lowest in the red group. There were no significant differences in serum protein carbonyl (PC) and malondialdehyde (MDA) contents. No statistical difference was recorded in blood lactate levels between the five groups. Turbot under red and orange light may have higher carbohydrate metabolism levels, characterized by higher blood glucose and hepatic glycogen content. Overall, the results of the current study suggested that light spectrum had a significant effect on the performance of juvenile turbot, with growth retardation, together with decreased antioxidative activity and pathogen resistance observed in the red and orange groups. Juveniles under blue spectrum exhibited the best growth performance, antioxidative activity and pathogen resistance. Thus, blue spectrum is suggested for rearing juvenile turbot and improving fish welfare in aquaculture systems.

Effect of different LED lights spectrum on the in vitro germination of gac seed (Momordica cochinchinensis)

Momordica cochinchinensis, also known as gac, is an indigenous fruit that can commonly found in Southeast Asia. Studies had shown that M. cochinchinensis contained a higher level of carotenoids, β-carotene, and lycopene compared to other vegetables and fruits. The present study was conducted to study the effect of light conditions on gac seeds germination and effect of light-emitting diode (LED) spectra (violet, blue, green, and red) on shoot, root, and leaf formation from germinated gac seeds. A total of 60 surface sterilised uncoated gac seeds were cultured in MS media where half of them exposed to sunlight while another half kept in the enclosed cupboard. Germinated seeds were then transferred to new MS media which contained 1 mg/L of BAP and cultured under different LED lights. Gac seeds germinated well in 12 hours light treatment at the rate of 75% after one week while dark treated seeds did not germinate at all. The green LED light spectrum was the most effective for the production of the highest mean number of shoots at 4.75 ± 0.63. On the other hand, the violet LED was the most effective spectrum in producing the highest number of roots, which was 7.50 ± 0.58. Meanwhile green LED produced the highest root length of 6.25 ± 0.25 cm. Besides, green LED treatment also able to induce the highest number of leaves, which was 10.21 ± 1.89. Lateral shoot and tendrils were developed on blue LED spectrum treated seed. In conclusion, light facilitates gac seed germination while the green LED light induced better characteristics of gac plant.

Defect Structure and Evolution of GaN-Based Light-Emitting Diodes on Planar and Cone-Patterned Sapphire Substrates

Epitaxial layers of GaN and InGaN/GaN multi-quantum well light emitting diodes (LEDs) were prepared both on cone-shaped patterned sapphire substrates and conventional sapphire substrates. The mechanism of nucleation of GaN epilayers was studied using metallographic and atomic force microscope images of the surface of GaN epilayers, and the internal factors of cone-shaped patterned sapphire substrates that accelerate GaN transverse growth and improve the quality of epitaxial layers were analyzed. The microstructural properties of GaN epitaxial layers grown on a patterned sapphire substrate were studied in detail using transmission electron microscopy to determine the distribution and growth. The surface morphology of p-GaN was characterized by scanning electron microscopy, and some other information about the defects was obtained. The full width at half maximum of electroluminescence spectra of LED grown on the patterned sapphire substrate is small, and its monochromaticity is good.

Effect of the light spectrum of white LEDs on the productivity of strawberry transplants in a plant factory with artificial lighting

The application of plant factory with artificial lighting (PFAL) for producing strawberry transplants (S-PFAL) was recently introduced due to the capacity for high quality and year-round transplant production. To achieve greater efficiency with this system, it is essential to select lighting sources that have a suitable spectrum for runner plant propagation. This study was conducted to investigate the effects of the light spectrum of white light-emitting diodes (LEDs), which have a different correlated color temperature compared with that of white fluorescent lamps, on the growth of strawberry (Fragaria × ananassa Duch. cv. Maehyang) propagules and runner plants in a PFAL. Uniform propagules with one fixed runner each were placed into a PFAL for transplant production and were grown under either warm-white LEDs (WWL), mint-white LEDs (MWL), or cool-white fluorescent lamps (CWF) for 21 days. The propagules in the MWL treatment group had the greatest number of leaves, leaf area, top/root dry weight ratio and number of newly formed runners per propagule among the treatments. The dry weight of the newly formed runners of each propagule was also greatest after MWL treatment, whereas it was lowest after CWF treatment. However, there was no significant difference in the growth parameters of the runner plants among the three treatments. The photosynthetic photon efficacy of WWL and MWL was 5.40 µmol s− 1 W− 1, which was 62.6% higher than that of CWF (3.38 µmol s− 1 W− 1). The dry weight efficacies of the MWL, WWL, and CWF treatments were 23.5, 22.1, and 10.0 g kWh− 1, respectively. These results indicate that MWL with high photosynthetic photon efficacy can have positive effects on the runner formation and growth of strawberry propagules and can replace cool-white fluorescent lamps in an S-PFAL.

Secondary metabolites, carbohydrate accumulation, and nutrient uptake in Aralia elata (Miq.) Seem seedlings exposed to shoot cutting and different LED spectra

Aralia elata is a famous homology of traditional medicine and wild vegetable due to its enriched content of flavonoids and saponins. Heavy exploration for shoots has nearly resulted in the exhaustion of the natural reserve of this species, but its traditional culture regime largely depends on land use in the long term. In this study, 1-year-old A. elata seedlings were cultured in commercial substrate under a plant factory condition where lighting was supplied by light-emitting diode (LED) panels in two bionic spectra of 16.9% red (R), 77.8% green (G), and 5.4% blue (B) (R2G4B2) and 12.5% R, 84.6% G, and 2.9% B (R2G10B1) to mimic the understory sunlight in natural populations. An artificial spectrum of 26.6% R, 59.9% G, and 13.5% B (R2G1B3) was also involved as the comparison. All LED lighting had a daily photoperiod of 18 h at the photosynthetic photon flux rate of 150 μmol m−2 s−1. Seedlings were fed by exponential fertilization at the rate of 140 mg nitrogen (N) plant−1[N–phosphorus (P)2O5–potassium (K)2O, 9–30–20]. Shoots were harvested twice with a midway cutting. The R2G10B1 spectrum promoted concentrations of N, P, starch, and total saponins in the secondly harvested shoots, where the R2G4B2 spectrum enhanced stem length, fresh weight, N content, and total saponin content per sprouted shoot. Total flavonoid content had a positive correlation with weight and contents of N, P and sugars, but the positive correlation of total saponins was only with weight. The drastic decline of sprout density in the second harvest decreased the content of total saponins in grouped A. elata seedlings. We conclude that light spectra and shoot cutting had a combined effect on biomass accumulation and total saponins which can be promoted in shoot-cut A. elata seedlings in the R2G4B2 spectrum under plant factory condition.

Nutrient assimilation and utilization in korean pine (Pinus koraiensis) seedlings exposed to exponential fertilization under contrasting spectra

ABSTRACT Pine trees are important for the agroforestry ecosystem due to their significance in nut production and ecological restoration. Korean pine (Pinus koraiensis Siebold & Zucc.) seedlings were cultured as model materials exposed to exponential fertilization (EF) at rates of 20 (E20), 80 (E80), and 140 mg nitrogen (N) plant−1 (E140) under high-pressure sodium (HPS) lamps (proportion in photosynthetic photon flux density: 43.9% red, 54.7% green, and 1.5% blue lights) and light-emitting diode (LED) (6.6% red, 75% green, and 8.4% blue lights) spectra. A high rate of EF at 140 mg N plant−1 under the LED spectrum tended to increase shoot biomass at the cost of phosphorus (P) dilution due to P assimilation through acid phosphatase activity and starch depletion. The uptake of N was not used for utilization but instead, for N storage in the biomass that assimilated through glutamine synthetase activity. Therefore, we conclude that the assimilation and utilization of P determined the growth and biomass in Korean pine seedlings while N can be absorbed and stored for reserve.

Supplemental Far-red Light-emitting Diode Light Increases Growth of Foxglove Seedlings Under Sole-source Lighting

Seedlings may be grown indoors where environmental conditions can be precisely controlled to ensure consistent and reliable production. The optimal spectrum for production under sole-source lighting is currently unknown. Far-red light (λ = 700–800 nm) typically is not a significant part of the spectrum of light-emitting diode (LED) grow lights. However, far-red light is photosynthetically active and can enhance leaf elongation, which may result in larger leaves and increased light interception. We hypothesized that adding far-red light to sole-source lighting would increase the growth of ‘Dalmatian Peach’ foxglove (Digitalis purpurea) seedlings grown under white LED lights, potentially shortening production times. Our objective was to evaluate the effect of far-red light intensities, ranging from 4.0 to 68.8 µmol·m−2·s−1, on the growth and morphology of foxglove seedlings. Foxglove seedlings were grown in a growth chamber with a photosynthetic photon flux density (PPFD) of 186 ± 6.4 μmol·m−2·s−1 and supplemental far-red light intensities ranging from 4.0 to 68.8 µmol·m−2·s−1. As far-red light increased, shoot dry weight, root dry weight, plant height, and plant height/number of leaves increased by 38% (P = 0.004), 20% (P = 0.029), 38% (P = 0.025), and 34% (P = 0.024), respectively, while root weight fraction decreased 16% (P = 0.034). Although we expected supplemental far-red light to induce leaf and/or stem expansion, specific leaf area and compactness (two measures of morphology) were unaffected. Because a 37% increase in total photon flux density (PPFD plus far-red light) resulted in a 34.5% increase in total plant dry weight, the increased growth likely was due to increased photosynthesis rather than a shade-acclimation response. The growth response was linear across the 4.0 to 68.8 µmol·m−2·s−1 range of far-fed light tested, so we were unable to determine a saturating far-red photon flux density.

Leaf development and energy yield of hydroponic sweetpotato seedlings using single-node cutting as influenced by light intensity and LED spectrum

Vine cuttings with six to eight unfolded leaves are utilized as is conventional in sweetpotato (Ipomoea batatas (L.) Lam.) seedling production. However, most vine cuttings wilt after transplanting into the field. Moreover, few researchers have examined the influence of photon flux density (PFD) provided by white or white plus red light-emitting diodes (LEDs) on sweetpotato plantlets. In this study, hydroponic sweetpotato (cv. Beniharuka) seedlings using single-node cutting were grown under 20 combinations of five levels of PFDs of 150, 200, 250, 300, and 350 μmol m−2 d−1 and four light qualities: white LEDs with a red light to blue light ratio (R:B ratio) of 0.9, white plus red LEDs with R:B ratios of 1.2 and 2.2, respectively, and fluorescent lamp with an R:B ratio of 1.8 as control, for 20 days under a controlled enviroment. Results showed that the number of newly developed leaves on hydroponic sweetpotato seedlings increased with time in a quadratic function, regardless of light quality. Fluorescent lamps led to greater numbers of new leaves on hydroponic sweetpotato seedlings compared with those grown under LEDs. Plant height, leaf area, and fresh and dry weights increased initially and then decreased with increasing daily light integral (DLI) in quadratic funcitons with a highest value under a PFD of 250 μmol m−2 d−1. However, no significant differences were observed in fresh and dry weights of hydroponic sweetpotato seedlings grown under PFDs of 200 and 250 μmol m−2 s−1. The quantum yield of photosystem II (ФPSII) decreased linearly as DLI increased from 8.6–20.2 mol m−2 d−1. Power consumptions based on fresh and dry weights were lowest in sweetpotato seedlings grown under a PFD of 200 μmol m−2 s−1 provided by white LEDs with an R:B ratio of 0.9. White LEDs also showed higher light energy use efficiency than white plus red LEDs. In summary, it is recommended that a PFD of 200 μmol m−2 s−1 with DLI at 11.5 mol m−2 d−1 provided by white LEDs with an R:B ratio of 0.9 is suitable for hydroponic sweetpotato (cv. Beniharuka) seedling production under a controlled environment.

A new double perovskite CaY0.5Ta0.5O3:Mn4+ deep-red phosphor: Synthesis, optical properties, and potential applications in plant-growth LEDs

Deep-red emitting CaY0.5Ta0.5O3:Mn4+ phosphors were obtained by optimizing the reaction temperature. The structure of CaY0.5Ta0.5O3:Mn4+ consisted of a double perovskite with the Pnma (62) space group. The luminescence intensity of the synthesized CaY0.5Ta0.5O3:0.3%Mn4+ at 1550 °C was twice as strong as that at 1500 °C. The photoluminescence spectra of the synthesized CaY0.5Ta0.5O3:Mn4+ phosphor exhibited a deep-red broadband luminescence from 650 nm to 750 nm with a 680 nm dominated peak due to the 2Eg→4A2g transition of Mn4+ in TaO6 octahedral structures. The optimal concentration for the CaY0.5Ta0.5O3:xMn4+ phosphor was 0.3 mol.%. The concentration quenching effect was ascribed to the dipole–quadrupole interaction. The decay time (0.398–0.171 ms) indicated that the forbidden character of 3d transitions existed among Mn4+. The crystal field strength and the Racah parameters were discussed to estimate the nephelauxetic effect of Mn4+ in the CaY0.5Ta0.5O3 host. Besides, the red light-emitting diodes (LEDs) were packaged using the CaY0.5Ta0.5O3:0.3%Mn4+ phosphor and a 368 nm near-ultraviolet chip. The emission spectrum of the red LED overlapped with the absorption curves of chlorophylls a and b. Results indicated that the CaY0.5Ta0.5O3:Mn4+ can serve as a component of the deep-red light in plant-growth LEDs.

LED lighting system for better color rendition space: the effect of color rendering index

ABSTRACT This study was conducted to investigate Color Rendering Index (CRI) recommendations for light emitting diode (LED) lighting in spaces needing better color rendition. Four LED spectra, that is, two spectra at Commission Internationale de l’Eclairage (CIE) Ra < 80 (79 and 76) and two spectra at CIE Ra ≥ 80 (83 and 84) were used in this study. The CIE Ra lacks accuracy in predicting perceived color quality, and the Fidelity Index and the Gamut Index were used to complement the weakness of CIE Ra. These metrics were combined to quantify the average increase or decrease in chroma. One hundred ninety-four participants evaluated retail-related tasks under different lighting conditions. The results showed that the CIE Ra had significant effects on preference, brightness perception, liveliness, and arousal. LED lights with CIE Ra < 80 received higher scores for preference, brightness perception, liveliness, and arousal than LED lights with CIE Ra ≥ 80, indicating that CIE Ra < 80 is the proper level for LED lighting in spaces needing better color rendition.

White-light emitting diodes’ spectrum effect on photosynthesis and nutrient use efficiency in Podocarpus macrophyllus seedlings

Fast urbanization and population increase resulted in the demand for ornamental seedling supply in a high efficiency under the culture of continuous artificial lighting. Light emitting diode (LED) can be considered as the replacement of high-pressure sodium (HPS) lamps by providing lights with specific wavelengths for plant growth at low energy cost. In this study, nutrient use efficiency was detected in Podocarpus macrophyllus seedlings under lighting spectra generated by white light-emitting diodes (LEDs) (red (R)/green (G)/blue (B)=8.4:75:16.6) and high-pressure sodium (HPS) lamps (R/G/B/=4.3:69.3:26.5). Compared to seedlings under the HPS spectrum, those under white LED spectrum had better growth, greater biomass accumulation, higher photosynthesis and gas exchange. In contrast, LED-spectrum treated seedlings had greater nitrogen (N) and phosphorus (P) contents than HPS-spectrum treated ones. The LED spectrum promoted nutrient use index for both N and P in seedlings compared to the HPS spectrum. The LED spectrum induced steady-state uptake of P but resulted in the dilution of N. In conclusion, white LED can be considered to replace the usage of HPS lamps for the culture of tree seedlings due to the spectrum effect on N utilization, P uptake and the use efficiencies of N and P.

Effects of Daily Light Integral and LED Spectrum on Growth and Nutritional Quality of Hydroponic Spinach

To achieve clean and high-quality spinach production, the effects of daily light integral (DLI) and light spectrum on growth, nutritional quality, and energy yield of hydroponic spinach (Spinacia oleracea L.) were investigated in a closed plant factory under light-emitting diode (LED) lighting. The hydroponic spinach plants were grown under 16 combinations of four levels of DLI (11.5, 14.4, 17.3, and 20.2 mol m−2 day−1) with four light spectra: LED lamps with ratio of red light to blue light (R:B ratio) of 0.9, 1.2, and 2.2 and fluorescent lamps with R:B ratio of 1.8 as control. The results show that total fresh and dry weights, energy yield, and light energy use efficiency (LUE) of harvested spinach were higher under D17.3-L1.2 treatment compared to other treatments. The higher net photosynthetic rates were shown at DLI of 17.3 mol m−2 day−1 regardless of light quality. Higher vitamin C contents of spinach in all LED treatments were obtained compared with the control. L1.2 treatments with higher fraction of blue light led to more vitamin C content, lower nitrate content, and higher LUE independent of DLI. L2.2 treatment with more fraction of red light was beneficial to reduce oxalate accumulation. Power consumption based on increased total fresh weight under LED lamps with R:B ratio of 1.2 in different DLIs was over 38% lower than that under the fluorescent lamps and 1.73 kWh per 100 g FW at DLI of 17.3 mol m−2 day−1. In conclusion, lighting environment in DLI of 17.3 mol m−2 day−1 using LED lamps with R:B ratio of 1.2 is suggested for the design of a LED plant factory for hydroponic spinach production.

A Novel New Light Recipe Significantly Increases the Growth and Yield of Sweet Basil (Ocimum basilicum) Grown in a Plant Factory System

Light is a crucial element for plant growth and production. High-pressure sodium (HPS) lamps are considered not very electrically efficient as they generate high radiant heat, and as a consequence, there has been a lot of interest in replacing HPS lamps with new more efficient lighting sources in the form of light-emitting diodes (LEDs). LEDs have a linear photon output with the electrical input current, and this great feature allows the design of lighting arrays that match the plant’s needs. In the current study, light spectrum absorbance of pigments extracted from 14 plant species was analyzed. Two absorbance peaks were observed in the Photosynthetically Active Radiation (PAR) region: one at 435 nm and the other at 665 nm. The light spectrum array was designed to produce the spectrum absorbed by basil pigments. This included the use of new wavelengths of 435 ± 5 nm to cover the blue region. Moreover, the ratio between blue and red was considered to match the absorbance of basil pigment. The use of a light spectrum that matches the plant absorbance significantly improved the investigated physiological parameters and increased the growth yield of basil. Moreover, this is the first to confirm the great positive impact of using 435 nm light spectrum in comparison with the commercially widely used 450 nm LED spectrum. This investigation has great scientific and commercial applications in the field of indoor faming and plant factory systems.

The effect of artificial solar spectrum on growth of cucumber and lettuce under controlled environment

Light-emitting diodes (LEDs) have been widely applied in the controlled environment agriculture, which are characterized by relatively narrow-band spectra and energetical efficiency. Most recently, the spectrum of Sunlike LEDs has been engineered and it closely resembles solar spectrum in the range of photosynthetic active radiation (PAR, 400–700 nm). To investigate how plant growth responses to the spectrum of Sunlike LEDs, cucumber and lettuce plants were cultivated and their responses were compared with the conventional white LEDs as well as composite of red and blue LEDs (RB, R/B ratio was 9:1). We observed that although Sunlike LEDs resulted in a longer stem in cucumber, dry weight and leaf area were similar as those under RB LEDs, and significantly higher than those under white LEDs. Moreover, cucumber leaves grown under Sunlike and white LEDs showed higher photosynthetic capacity than those grown under RB LEDs. For lettuce, plants grown under Sunlike LEDs showed larger leaf area and higher dry weight than the other two treatments. However, the leaf photosynthetic capacity of lettuce grown under Sunlike LEDs was the lowest. In this context, the spectrum induced plant functions are species-dependent. Furthermore, the three types of LEDs show distinct light spectra and they are different in many aspects. Therefore, it is difficult to attribute the different plant responses to certain specific light spectra. We conclude that plants grown under Sunlike LEDs exhibit larger leaf area, which may be due to some specific spectrum distributions (such as more far-red radiation), and consequently are favorable for light interception and therefore result in greater production.