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Solar simulators are instruments used for controllable measurements of the properties of solar cells in indoor environments. The purpose of this paper is to examine the peculiarities of the photoresponses of CdTe/CdSeTe and microcrystalline Si solar cells and to reveal the pathways to reduction of spectrum mismatch effects when using light-emitting diode (LED)-based or hybrid LED and halogen lamp-based solar simulators of an A+-class spectrum with a small number of sources. While only four different LED types are needed to achieve an A+-class spectrum under updated IEC 60904-9:2020 standard requirements, as demonstrated by our results, additional ultraviolet LEDs are necessary to reduce the spectrum mismatch. For hybrid solar simulator configurations, the combination of cool white LED arrays and halogen emitters can serve as a main light source. Optimized for both solar cell types, hybrid simulators have a lower spectral deviation and better spectrum coverage compared to LED-only simulators with the same number of distinct source types. In addition, our results predict lower spectral mismatch errors for optimized simulators when compared with conventional Xe lamp-based simulators. [ABSTRACT FROM AUTHOR]

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 [ABSTRACT FROM AUTHOR]

Ultraviolet A (UV-A) light-emitting diodes (LEDs) could serve as an effective tool for improving the content of health-promoting bioactive compounds in plants in controlled-environment agriculture (CEA) systems. The goal of this study was to investigate the effects of UV-A LEDs at different wavelengths (366, 390, and 402 nm) and durations (10 and 16 h) on the growth and phytochemical contents of mustard microgreens (Brassica juncea L. cv. "Red Lion"), when used as supplemental light to the main LED lighting system (with peak wavelengths of 447, 638, 665, and 731 nm). Plants were grown for 10 days under a total photon flux density (TPFD) of 300 µmol m−2 s−1 and 16-h light/8-h dark period. Different UV-A wavelengths and irradiance durations had varied effects on mustard microgreens. Supplemental UV-A radiation did not affect biomass accumulation; however, the longest UV-A wavelength (402 nm) increased the leaf area of mustard microgreens, regardless of the duration of irradiance. The concentration of the total phenolic content and α-tocopherol mostly increased under 402-nm UV-A, while that of nitrates increased under 366- and 390-nm UV-A at both radiance durations. The contents of lutein/zeaxanthin and β-carotene increased in response to the shortest UV-A wavelength (366 nm) at 10-h irradiance as well as longer UV-A wavelength (390 nm) at 16 h irradiance. The most positive effect on the accumulation of mineral elements, except iron, was observed under longer UV-A wavelengths at 16-h irradiance. Overall, these results suggest that properly composed UV-A LED parameters in LED lighting systems could improve the nutritional quality of mustard microgreens, without causing any adverse effects on plant growth. [ABSTRACT FROM AUTHOR]

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This study examines the effect of irradiance level produced by solid-state light-emitting diodes (LEDs) on the growth, nutritional quality and antioxidant properties of Brassicaceae family microgreens. Kohlrabi ( Brassica oleracea var. gongylodes, 'Delicacy Purple') mustard ( Brassica juncea L., 'Red Lion'), red pak choi ( Brassica rapa var. chinensis, 'Rubi F') and tatsoi ( Brassica rapa var. rosularis) were grown using peat substrate in controlled-environment chambers until harvest time (10 days, 21/17°C, 16 h). A system of five lighting modules with 455, 638, 665 and 731 nm LEDs at a total photosynthetic photon flux densities (PPFD) of 545, 440, 330, 220 and 110 µmol ms respectively were used. Insufficient levels of photosynthetically active photon flux (110 µmol m s) suppressed normal growth and diminished the nutritional value of the Brassica microgreens studied. In general, the most suitable conditions for growth and nutritional quality of the microgreens was 330-440 µmol m s irradiation, which resulted in a larger leaf surface area, lower content of nitrates and higher total anthocyanins, total phenols and 2,2-diphenyl-1-picrylhydrazyl (DPPH) free-radical scavenging capacity. High light levels (545 µmol m s), which was expected to induce mild photostress, had no significant positive impact for most of investigated parameters. [ABSTRACT FROM AUTHOR]

The objective of this study was to evaluate how different UV-A wavelengths influence the morphology and photosynthetic behavior of red-leaf lettuce (Lactuca sativa L. cv. Maiko). In the experiments, the main photosynthetic photon flux consisted of red (R) and blue (B) light, supplemented with equal doses of different UV-A wavelengths (402, 387 and 367 nm). Treating the crops with low dosages of specific narrow-band UV-A radiation at key points in the life cycle initiated a cascade of responses in the above-ground biomass. According to the results, red-leaf lettuces acclimated to longer UV-A wavelengths by increasing biomass production, whereas different UV-A wavelengths had no significant effect on plant senescence reflectance, nor on the normalized difference vegetation index. A significant decrease in the maximum quantum yield of the PSII photochemistry of dark (Fv/Fm) and light (ΦPSII) adapted plants was observed. A lack of significant changes in non-photochemical fluorescence quenching indicates that photo-inhibition occurred under RBUV367, whereas the photosynthetic response under RB, RBUV402, and RBUV387 suggests that there was no damage to PSII. The correlation of the photosynthetic rate (Pr) with the stomatal conductance (gs) indicated that the increase in the Pr of lettuce under supplemental UV-A radiation was due to the increase of gs, instead of the ratio of the intracellular to ambient CO2 content (Ci/Ca) or stomatal limitations. [ABSTRACT FROM AUTHOR]

Mustard, beet and parsley were grown to harvest time under selected LEDs: 638 + 660 + 731 + 0% 445 nm; 638 + 660 + 731 + 8% 445 nm; 638 + 660 + 731 + 16% 445 nm; 638 + 660 + 731 + 25% 445 nm; 638 + 660 + 731 + 33% 445 nm. From 1.2 to 4.3 times higher concentrations of chlorophylls a and b , carotenoids, α- and β-carotenes, lutein, violaxanthin and zeaxanthin was found under blue 33% treatment in comparison to lower blue light dosages. Meanwhile, the accumulation of metabolites, which were not directly connected with light reactions, such as tocopherols, was more influenced by lower (16%) blue light dosage, increasing about 1.3 times. Thus, microgreen enrichment of carotenoid and xanthophyll pigments may be achieved using higher (16–33%) blue light intensities. Changes in metabolite quantities were not the result of changes of other carotenoid concentration, but were more influenced by light treatment and depended on the species. Significant quantitative changes in response to blue light percentage were obtained for both directly and not directly light-dependent metabolite groups. [ABSTRACT FROM AUTHOR]

The objective of this study was to evaluate the effects of irradiance levels and spectra produced by solid-state light-emitting diodes (LEDs) on carotenoid content and composition changes in Brassicaceae microgreens. A system of five high-power, solid-state lighting modules with standard 447-, 638-, 665-, and 731-nm LEDs was used in the experiments. Two experiments were performed: (1) evaluation of LED irradiance levels of 545, 440, 330, 220, and 110 μmol m −2 s −1 photosynthetically active flux density (PPFD) and (2) evaluation of the effects of 520-, 595-, and 622-nm LEDs supplemental to the standard set of LEDs. Concentrations of various carotenoids in red pak choi and tatsoi were higher under illumination of 330–440 μmol m −2 s −1 and at 110–220 μmol m −2 s −1 in mustard. All supplemental wavelengths increased total carotenoid content in mustard but decreased it in red pak choi. Carotenoid content increased in tatsoi under supplemental yellow light. [ABSTRACT FROM AUTHOR]

• Primary metabolites in lettuce interplay with nutritional value and safety of food. • Lettuce sensitivity to lighting spectrum is determined by its metabolic plasticity. • The effect of supplemental orange, green, yellow and UV-A light is cultivar specific. • Green light has moderate positive impact on nutritive primary metabolites in lettuce. • Green, orange and UV-A light has distinct effect on primary metabolites. In this study we explore the effects of multi-colour LED lighting spectrum on nutritive primary metabolites in green ('Lobjoits green cos') and red ('Red cos') leaf lettuce (Lactuca sativa L.), cultivated in controlled environment. The basal lighting, consisting of blue 455 nm, red 627 and 660 nm and far red 735 nm LEDs, was supplemented with UV-A 380 nm, green 510 nm, yellow 595 nm or orange 622 nm LED wavelengths at total photosynthetic photon flux density of 300 μmol m−2 s−1. Supplemental lighting colours did not affect lettuce growth; however had distinct impact on nitrite, amino acid, organic acid, and soluble sugar contents. Orange, green and UV-A light had differential effects on red and green leaf lettuce metabolism and interplay with nutritional value and safety of lettuce production. The metabolic response was cultivar specific; however green light had reasonable impact on the contents of nutritive primary metabolites in red and green leaf lettuce. [ABSTRACT FROM AUTHOR]