Far-red LED Research Articles

Investigating the influence of varied ratios of red and far-red light on lettuce (Lactuca sativa): effects on growth, photosynthetic characteristics and chlorophyll fluorescence.

Far red photon flux accelerates photosynthetic electron transfer rates through photosynthetic pigments, influencing various biological processes. In this study, we investigated the impact of differing red and far-red light ratios on plant growth using LED lamps with different wavelengths and Ca1.8Mg1.2Al2Ge3O12:0.03Cr3+ phosphor materials. The control group (CK) consisted of a plant growth special lamp with 450 nm blue light + 650 nm red light. Four treatments were established: F1 (650 nm red light), F2 (CK + 730 nm far-red light in a 3:2 ratio), F3 (650 nm red light + 730 nm far-red light in a 3:2 ratio), and F4 (CK + phosphor-converted far-red LED in a 3:2 ratio). The study assessed changes in red and far-red light ratios and their impact on the growth morphology, photosynthetic characteristics, fluorescence characteristics, stomatal status, and nutritional quality of cream lettuce. The results revealed that the F3 light treatment exhibited superior growth characteristics and quality compared to the CK treatment. Notably, leaf area, aboveground fresh weight, vitamin C content, and total soluble sugar significantly increased. Additionally, the addition of far-red light resulted in an increase in stomatal density and size, and the F3 treatments were accompanied by increases in net photosynthetic rate (Pn), transpiration rate (Tr), intercellular CO2 concentration (Ci), and stomatal conductance (Gs). The results demonstrated that the F3 treatment, with its optimal red-to-far-red light ratio, promoted plant growth and photosynthetic characteristics. This indicates its suitability for supplementing artificial light sources in plant factories and greenhouses.

Effect of ultraviolet and far-red LED light added to broad spectrum white LED on lettuce production in vertical farm

Effect of ultraviolet and far-red LED light added to broad spectrum white LED on lettuce production in vertical farm

Effect of inter-lighting using red+blue LEDs with additional far-red LED on fruit quality and carotenoid content of red- and yellow-colored sweet peppers

Effect of inter-lighting using red+blue LEDs with additional far-red LED on fruit quality and carotenoid content of red- and yellow-colored sweet peppers

High-performance Gd3Al4GaO12:Cr3+ phosphors for next-generation far-red LEDs

Far-red (FR) photosensitive pigment (PFR) is important for plant photomorphogenesis. Phosphor-converted (pc) LED is the next-generation FR light device. How to obtain FR-emitting phosphors with a good external quantum efficiency (EQE), suitable photoluminescence and high thermal stability is still a challenge. Herein, by optimizing the sintering technology and chemical design, we develop an excellent FR phosphor, Gd3Al4GaO12:Cr3+. The phosphor has an emission peak at 734 nm and a band width of 70 nm, matched well with the PFR absorption band. By adjusting the flux of H3BO3 and Cr3+ concentration, the EQE reaches 47.2%, and the thermal stability maintains 96.8% at 423 K. Because of its excellent optical properties, the power-conversion efficiency of the FR pc-LED reaches 24.0% driven at 100 mA, demonstrating the high performance and promising applications in the next-generation FR light source.

Double Perovskite Mn4+-Doped La2CaSnO6/La2MgSnO6 Phosphor for Near-Ultraviolet Light Excited W-LEDs and Plant Growth.

Non-rare earth doped oxide phosphors with far-red emission have become one of the hot spots of current research due to their low price and excellent physicochemical stability as the red component in white light-emitting diodes (W-LEDs) and plant growth. Herein, we report novel Mn4+-doped La2CaSnO6 and La2MgSnO6 phosphors by high-temperature solid-phase synthesis and analyzed their crystal structures by XRD and Rietveld refinement. Their excitation spectra consist of two distinct excitation bands with the dominant excitation range from 250 to 450 nm, indicating that they possess strong absorption of near-ultraviolet light. Their emission is located around 693 and 708 nm, respectively, and can be absorbed by the photosensitive pigments Pr and Pfr, proving their great potential for plant growth. Finally, the prepared samples were coated with 365 nm UV chips to fabricate far-red LEDs and W-LEDs with low correlation color temperature (CCT = 4958 K/5275 K) and high color rendering index (Ra = 96.4/96.6). Our results indicate that La2CaSnO6:Mn4+ and La2MgSnO6:Mn4+ red phosphors could be used as candidate materials for W-LED lighting and plant growth.

Low Oxygen Storage Improves Tomato Postharvest Cold Tolerance, Especially for Tomatoes Cultivated with Far-Red LED Light

We investigated the effects of low oxygen storage on chilling injury development, colour development, respiration and H2O2 levels of ‘Merlice’ tomatoes cultivated with and without far red (FR) LED lighting during 20 days of shelf-life. Mature green (MG) and red (R) tomatoes were stored at 2 °C in combination with 0.5, 2.5, 5 and 21 kPa O2 for 15 days (experiment 1). MG tomatoes cultivated under either white LED or white LED light with FR LED light were stored at 2 °C in combination with 1, 5 and 21 O2 kPa for 14 days (experiment 2). Chilled MG and R tomatoes from experiment 1 showed decay, firmness loss and higher weight loss during shelf-life which were reduced under low oxygen conditions. FR during cultivation improved chilling tolerance of MG tomatoes. Fastest colour development and lowest respiration rate during shelf-life were observed for MG fruit cultivated with FR lighting prior to storage at 1 kPa O2/0 kPa CO2. H2O2 levels during the shelf-life were not affected during cold storage. The improved cold tolerance of MG tomatoes cultivated with FR lighting is likely due to lower oxygen uptake that led to both higher lycopene synthesis and less softening.

The Photosensitizer Octakis(cholinyl)zinc Phthalocyanine with Ability to Bind to a Model Spike Protein Leads to a Loss of SARS-CoV-2 Infectivity In Vitro When Exposed to Far-Red LED.

Photodynamic inactivation of pathogenic microorganisms can be successfully used to eradicate pathogens in localized lesions, infected liquid media, and on various surfaces. This technique utilizes the photosensitizer (PS), light, and molecular oxygen to produce reactive oxygen species that kill pathogens. Here, we used the PS, water soluble octakis(cholinyl)zinc phthalocyanine (Zn-PcChol8+), to inactivate an initial 4.75–5.00 IgTCID50/mL titer of SARS-CoV-2, thereby preventing viral infection when tested in Vero E6 cell cultures. Zn-PcChol8+ in a minimally studied concentration, 1 µM and LED 3.75 J/cm2, completely destroyed the infectivity of SARS-CoV-2. To detect possible PS binding sites on the envelope of SARS-CoV-2, we analyzed electrostatic potential and simulated binding of Zn-PcChol8+ to the spike protein of this coronavirus by means of Brownian dynamics software, ProKSim (Protein Kinetics Simulator). Most of the Zn-PcChol8+ molecules formed clusters at the upper half of the stalk within a vast area of negative electrostatic potential. Positioning of the PS on the surface of the spike protein at a distance of no more than 10 nm from the viral membrane may be favorable for the oxidative damage. The high sensitivity of SARS-CoV-2 to photodynamic inactivation by Zn-PcChol8+ is discussed with respect to the application of this PS to control the spread of COVID-19.

Gene Expression Related to Steviol Glycoside Synthesis Produced in Stevia rebaudiana (Bert.) Shoot Culture Induced with High Far-Red LED Light in TIS RITA® Bioreactor System

Gene Expression Related to Steviol Glycoside Synthesis Produced in Stevia rebaudiana (Bert.) Shoot Culture Induced with High Far-Red LED Light in TIS RITA® Bioreactor System

Postharvest LED lighting: effect of red, blue and far red on quality of minimally processed broccoli sprouts.

The main objective of this study was to evaluate physiological and quality changes of minimally processed broccoli sprouts illuminated during postharvest storage under blue, red and far-red LED lighting as compared to darkness or illumination with fluorescent light, as control treatments. Morphological and microbiological changes were determined during 15 days at 5 °C. In addition, total antioxidant activity and bioactive compound changes throughout the shelf life were also monitored. Results showed that far-red LED lighting increased hypocotyl and sprout length, decreased microbial growth and improved the total antioxidant and scavenging activities, compared to darkness and fluorescent lighting treatments. However, it did not stimulate the biosynthesis of phenolic acids. In contrast, blue LED light reduced by 50% the total antioxidant capacity of broccoli sprouts compared to far-red treatment, as well as morphological development. In addition, total scavenging activity was increased under far-red LED light compared with the other treatments by 12-10% (darkness and fluorescence) and 33-31% (blue and red LEDs). Our results suggest that minimally processed sprouts may benefit from LED lighting during shelf life in terms of quality, although further experiments should be conducted to optimize a proper exposure cycle and intensity aiming for use in the distribution chain. The results also open the way for further development towards the integration of this technology in the food distribution chain.

Use of Combined Irradiation in Grow Light

Effective cultivation of plants with grow light is possible only under optical radiation of a certain spectral composition. The cheapest way to generate optical radiation is with the help of high pressure sodium lamps. However, their spectral composition is not fully acceptable for grow light. LEDs allow you to set almost any spectrum, but their cost is quite high. ( Research purpose ) To prove the spectral composition of the LED emitter-corrector used in grow light in addition to sodium lamps theoretically and practically. ( Materials and methods ) The authors experimentally studied the effectiveness of combined irradiation in the Laboratory of Energy Ecology of Grow Light at the Institute of Agroengineering and Environmental Problems of Agricultural Production under the irradiation of Blagovest tomato seedlings. They investigated the biometric indicators of plants. The production experiment was carried out in the greenhouse plant Mezhvidi (Latvia) on adult Encore tomato plants for three options: the first – under sodium lamps; the second – with LED irradiators; the third – with a combination of sodium lamps and corrector. The effect of the irradiator on the plants was evaluated by the magnitude of the fluctuating asymmetry of bilateral signs of the leaf blade. ( Results and discussion ) The authors found out that the use of the corrector improved the seedlings biometric parameters: increased the number of leaves, their wet weight, the content of chlorophyll and dry substance in them. It was noted that in the greenhouse the least favorable light environment was formed under sodium lamps, and LED irradiators created more comfortable conditions. They confirmed that the use of a corrector provided the best light environment. They revealed an increase in the yield of tomato fruits and their taste when using combined irradiation. ( Conclusions ) The authors proved that to correct the spectrum of HPS lamp 400, a corrector photon flux of 71.2 micromoles per second is required, while the ratio of blue and far-red LEDs fluxes should be 64 and 36 percent respectively.

Special issue in honour of Prof. Reto J. Strasser - JIP-test as a tool for early diagnostics of plant growth and flowering upon selected light recipe

Light is a major factor controlling plant growth and development. To assess the impact of the applied light conditions, we aimed to sort out a tool for early diagnostics of the plant physiological state. We investigated the effect of a blue:red:far-red LED light formula recommended for improved plant performance (flowering). High (BR) and low (BRS) light intensity variants were compared to normal (W) and 'shadowed' (WS) white fluorescent controls. The efficiency of the JIP-test to determine changes during early growth of pea plants was compared to additional physiological characteristics (growth parameters, thermal stability of the thylakoid membranes, chlorophyll content, CO2 assimilation, transpiration). Our data showed the onset of growth inhibition under BR light, while BRS light stimulated plants to reach the flowering stage similarly as the W control. We concluded that the JIP-test is appropriate for early, reliable, and nondestructive analysis of light recipes for plant growth and flowering.

Photoluminescence Properties of Novel Far-Red Emission Ca3Gd2W2O12:Mn4+ Phosphor

A series of Ca3Gd2W2O12:Mn4+ far-red phosphors were successfully synthesized by high temperature solid state reaction. The crystal phases and morphology of the powders were analyzed by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). The luminescent properties of the samples with varying Mn4+ concentrations were investigated, and the result indicates that prepared phosphor Ca3Gd2W2O12:Mn4+ can be excited by ultraviolet light and exhibit intense far red emission at 710 nm. The optimum doping concentration of Mn4+ is about 0.2 mol %. The internal quantum efficiency of Ca3Gd2W2O12:Mn4+ phosphors are 58.5%. In addition, the mechanism of luminescence is also analyzed by using Tanab-Sugano energy level diagram. The thermal stability of samples have been researched and discussed. Finally, a far-red LED was fabricated by combining a 365 nm near-ultraviolet InGaN chip with Ca3Gd2W2O12:Mn4+ phosphor. All the results indicated that Ca3Gd2W2O12:Mn4+ as an excellent phosphor can be applied to far-red LED lamp and it has potential applications in plant growth.

Far-red light during cultivation induces postharvest cold tolerance in tomato fruit

We investigated the role of far-red LED light during cultivation on postharvest cold tolerance in tomato fruit (Solanum lycopersicum cv Moneymaker). Red and blue top LED light, providing 150 μmol m−2 s-1 photo-synthetically active radiation (PAR) at plant height for 16 h daily, was combined with 0, 30 or 50 μmol m−2 s-1 (non-PAR) far-red LED light. Tomatoes were harvested at the mature green or red stage and subjected to cold storage for 0, 5, 10, and 15 d at 4 °C, followed by 20 d shelf-life at 20 °C.Mature green harvested tomatoes, cultivated with additional far-red light, showed reduced weight loss, less pitting, faster red colour development during shelf-life (when prior long cold stored), and less softening (when prior short or non-cold stored). FR lighting during cultivation likely protects the membrane integrity of MG tomatoes and thus allows uninterrupted lycopene synthesis. Red harvested tomatoes cultivated with additional far-red light were firmer at harvest, showed reduced weight loss and less decay during shelf-life. Less red colouration was observed for red harvested fruits at the start of shelf-life when fruits were prior cold stored, indicative of lycopene breakdown during cold storage. The improved cold tolerance of red harvested fruits grown under additional far-red light is likely due to higher firmness at the start of the shelf-life period with lycopene acting as antioxidant during cold storage. In conclusion, additional far-red light during cultivation improved postharvest cold tolerance for tomatoes harvested at both the green and red maturity stage, and might therefore be suitable to prolong the storage potential of tomato at sub-optimal temperatures.

Synthesis and photoluminescence properties of novel far-red-emitting BaLaMgNbO6:Mn4+ phosphors for plant growth LEDs.

A series of far-red-emitting BaLaMgNbO6:Mn4+ (BLMN:Mn4+) phosphors were successfully synthesized by a high-temperature solid-state reaction method. Crystal structure and luminescence properties of the obtained samples were systematically investigated. The emission spectra exhibited a strong narrow far-red emission band peaking at 700 nm with a full width at half-maximum (FWHM) of ∼36 nm under 360 nm excitation. The optimal Mn4+ concentration was about 0.4 mol%. The internal quantum efficiency and CIE chromaticity coordinates of the BLMN:0.4% Mn4+ phosphor were 52% and (0.7222, 0.2777), respectively. In addition, the luminescence mechanism has been analyzed using a Tanabe–Sugano energy level diagram. Finally, by using a 365 nm near-ultraviolet InGaN chip combined with BLMN:0.4% Mn4+ phosphors, a far-red LED device was fabricated.

Supplemental irradiation with far-red light-emitting diodes improves growth and phenolic contents in Crepidiastrum denticulatum in a plant factory with artificial lighting

The aim of this study was to analyze the growth and phytochemical composition of Crepidiastrum denticulatum, a valuable medicinal plant, in response to various periods of irradiation and ratios of far-red (FR) LED light combined with red (R) and blue (B) LED lights. Three-week-old C. denticulatum seedlings were transplanted to a hydroponic system in a plant factory equipped with R, B, and FR LEDs. The ratio of R to B LEDs was set at 8:2 (R8B2), and the ratio of R to FR LEDs was adjusted to 0.7, 1.2, 4.1, and 8.6. R8B2 (without FR LEDs) and commercial LEDs were used as control I and II, respectively. The plants were cultivated under these light treatments, and some of the control plants were subjected to four different R/FR ratios for 30 min before the end of the light period (EOL). We measured growth characteristics, total phenolic contents, and the levels of individual phenolic compounds (chlorogenic acid, caffeic acid, and chicoric acid) 6 weeks after treatment. Shoot fresh and dry weight, leaf area, leaf length, and leaf width under R/FR ratios of 0.7 and 1.2 were 1.8- to 2.4-times higher than those of the control plants. Continuous R/FR 0.7 and 1.2 irradiation reduced the total phenolic content per dry weight compared to the control, although this effect was not significant. The total phenolic content per plant under R/FR 0.7 and 1.2 increased more than 2-fold, and the shoot fresh weight increased 1.7- and 1.6-fold, compared to control I. Individual phenolic compound levels exhibited the same trends as total phenolic content. Under R/FR 0.7 and 1.2, chlorogenic acid, caffeic acid, and chicoric acid levels per shoot increased 1.3- to 1.8-fold compared to control I. FR EOL treatments did not have a significant effects on growth or the contents of bioactive compounds. These results suggest that supplemental irradiation with FR LEDs could be used to improve C. denticulatum growth and quality in terms of phytochemical composition when grown in a plant factory with artificial lighting.

Far-red LEDs improve fruit production in greenhouse tomato grown under high-pressure sodium lighting

Far-red LEDs improve fruit production in greenhouse tomato grown under high-pressure sodium lighting

Increase in biomass and bioactive compounds in lettuce under various ratios of red to far-red LED light supplemented with blue LED light

The aim of this study was to analyze the growth and bioactive compounds of lettuce in response to far-red LED light supplemented with a combination of red and blue LED light. Sixteen-day-old red leaf lettuce seedlings were transplanted to a growth chamber equipped with red, blue, and far-red LEDs. After setting the ratio of blue (B) to red (R) LEDs to 2:8, the ratio of R to far-red (FR) LEDs was adjusted to 0.7, 1.2, 4.1, or 8.6 (B+R/FR 0.7, 1.2, 4.1, or 8.6). Additionally, plants were irradiated with combined B and R LEDs (B+R) and fluorescent lamps (control) for 24 days. Growth characteristics including cell division rate, epidermal cell density and thickness, and antioxidant phenolic compounds were measured. Supplementation with FR LED light improved shoot and root growth compared to plants under B+R and control treatment. B+R/FR 1.2 treatment resulted in the highest shoot fresh weight and leaf area on day 24 of treatment. Obvious activation of the G2M phase was not observed in plants under far-red treatment, and most far-red treatments besides B+R/FR 4.1 increased the epidermal cell size. Plants treated with B+R/FR ratios of only 0.7 and 1.2 had significantly higher total phenolic levels, antioxidant activity, chlorogenic acid contents, and caffeic acid contents per plant than the control. These results suggest that supplementing the existing visual light spectrum, such as red and blue light, with far-red LEDs improves lettuce growth and bioactive compound content in a closed-type plant production system.

Harvesting Far-Red Light by Chlorophyll f in Photosystems I and II of Unicellular Cyanobacterium strain KC1.

Cells of a unicellular cyanobacterium strain KC1, which were collected from Japanese fresh water Lake Biwa, formed chlorophyll (Chl) f at 6.7%, Chl a' at 2.0% and pheophytin a at 0.96% with respect to Chl a after growth under 740 nm light. The far-red-acclimated cells (Fr cells) formed extra absorption bands of Chl f at 715 nm in addition to the major Chl a band. Fluorescence lifetimes were measured. The 405-nm laser flash, which excites mainly Chl a in photosystem I (PSI), induced a fast energy transfer to multiple fluorescence bands at 720-760 and 805 nm of Chl f at 77 K in Fr cells with almost no PSI-red-Chl a band. The 630-nm laser flash, which mainly excited photosystem II (PSII) through phycocyanin, revealed fast energy transfer to another set of Chl f bands at 720-770 and 810 nm as well as to the 694-nm Chl a fluorescence band. The 694-nm band did not transfer excitation energy to Chl f. Therefore, Chl a in PSI, and phycocyanin in PSII of Fr cells transferred excitation energy to different sets of Chl f molecules. Multiple Chl f forms, thus, seem to work as the far-red antenna both in PSI and PSII. A variety of cyanobacterial species, phylogenically distant from each other, seems to use a Chl f antenna in far-red environments, such as under dense biomats, in colonies, or under far-red LED light.

閉鎖型苗生産システムにおける遠赤色LED光がトマト苗の生育に及ぼす影響

明期終了時の短時間の光照射 (EOD光照射) の処理では, PSSがEOD-B区で0.56, EOD-R区で0.89およびEOD-FR区で0.13となった. PSSが最も低いEOD-FR区で茎伸長が促進され, 徒長した. 一方，第1花房着生葉位は試験区間で差がみられなかった. よって, EOD-FR処理によりトマトの避陰反応が誘導されることが示されたが, 花成は促進されなかった. 他方, 明期 (16 h) における遠赤色光量を調節した実験では, 第1花房着生葉位は試験区間で差がみられず, 低R/FR比の遠赤色光が含まれる全処理区で高R/FR比のFR0区と比べて茎伸長が促進され, 徒長した. よって, 明期 のPSSが0.72以下のFR50区、FR100区およびFR150区で避陰反応は誘導するため, 一次育苗で遠赤色光を付加する必要はないことが示唆された. 以上より, EOD-FR処理や低R/FRの条件では, 花成を促進することはなく, 茎伸長を促進するため，閉鎖型苗生産システムではこのような光環境制御は望ましくないと考えられた.

Does light spectral quality affect survival and regeneration of potato (Solanum tuberosum L.) shoot tips after cryopreservation?

Cryopreservation, the storage of germplasm at ultra-low temperature is the most reliable tool for long-term preservation of plant genetic resources. Cryopreservation techniques are widely applied but the effect of light spectra on plant recovery after cryopreservation is largely unknown. Therefore, we investigated the effect of different light spectral qualities on survival and regeneration of shoot tips of potato (Solanum tuberosum L.) cultivars Agrie Dzeltenie, Maret, Bintje, Desiree and Anti cryopreserved by the DMSO-droplet method. Prior to cryopreservation, the plants were stored under cool white fluorescent light (CW). Post-cryopreservation, the plants were allowed to regenerate under six different light qualities: CW, warm white light (HQI), blue LEDs (B), red LEDs (R), red with 10 % of blue (RB) and RBF - red with 10 % of blue with addition of 20 % of far-red LEDs. The light spectral quality had a significant effect on the survival and regeneration of potato shoot tips after cryopreservation. The combination of red light with 10 % of blue (RB) doubled the regeneration percentage of all cultivars, whereas red light (R) was not suitable for regeneration after cryopreservation. Specifically, the regeneration percentages were increased in RB compared to CW from 25.5 to 52.6 % for ‘Agrie Dzeltenie’, 25.0–43.6 % for ‘Maret’, 8.1–26.1 % for ‘Bintje’, 0.0–17.1 % for ‘Anti’ and 18.2–36.6 % for ‘Desiree‘. Therefore, the modification of light spectra during the recovery phase is a promising tool for increasing the regeneration of potato shoot tips after cryopreservation.