Impact Of Light Intensity Research Articles

Impact of Light Intensity on Control in Photoinduced Organocatalyzed Atom Transfer Radical Polymerization.

Organic photoredox catalysts have been shown to operate organocatalyzed atom transfer radical polymerizations (O-ATRP) using visible light as the driving force. In this work, the effect of light intensity from white LEDs was evaluated as an influential factor in control over the polymerization and the production of well-defined polymers. We posit the irradiation conditions control the concentrations of various catalyst states necessary to mediate a controlled radical polymerization. Systematic dimming of white LEDs allowed for consideration of the role of light intensity on the polymerization performance. The general effects of decreased irradiation intensity in photoinduced O-ATRP were investigated through comparing two different organic photoredox catalysts: perylene and an 3,7-di(4-biphenyl) 1-naphthalene-10-phenoxazine. Previous computational efforts have investigated catalyst photophysical and electrochemical characteristics, but the broad and complex effects of varied irradiation intensity as an experimental variable on the mechanism of O-ATRP have not been explored. This work revealed that perylene requires more stringent irradiation conditions to achieve controlled polymer molecular weight growth and produce polymers with dispersities <1.50. In contrast, the 3,7-di(4-biphenyl) 1-naphthalene-10-phenoxazine is more robust, achieving linear polymer molecular weight growth under relative irradiation intensity as low as 25%, to produce polymers with dispersities <1.50. This finding is significant, as the discovery of highly robust catalysts is necessary to allow for the adoption of successful O-ATRP in a wide scope of conditions, including those which necessitate low light intensity irradiation.

Impact of light intensity and quality on chromatophore and nuclear gene expression in Paulinella chromatophora, an amoeba with nascent photosynthetic organelles.

Plastid evolution has been attributed to a single primary endosymbiotic event that occurred about 1.6 billion years ago (BYA) in which a cyanobacterium was engulfed and retained by a eukaryotic cell, although early steps in plastid integration are poorly understood. The photosynthetic amoeba Paulinella chromatophora represents a unique model for the study of plastid evolution because it contains cyanobacterium-derived photosynthetic organelles termed 'chromatophores' that originated relatively recently (0.09-0.14BYA). The chromatophore genome is about a third the size of the genome of closely related cyanobacteria, but 10-fold larger than most plastid genomes. Several genes have been transferred from the chromatophore genome to the host nuclear genome through endosymbiotic gene transfer (EGT). Some EGT-derived proteins could be imported into chromatophores for function. Two photosynthesis-related genes (psaI and csos4A) are encoded by both the nuclear and chromatophore genomes, suggesting that EGT in Paulinella chromatophora is ongoing. Many EGT-derived genes encode proteins that function in photosynthesis and photoprotection, including an expanded family of high-light-inducible (ncHLI) proteins. Cyanobacterial hli genes are high-light induced and required for cell viability under excess light. We examined the impact of light on Paulinella chromatophora and found that this organism is light sensitive and lacks light-induced transcriptional regulation of chromatophore genes and most EGT-derived nuclear genes. However, several ncHLI genes have reestablished light-dependent regulation, which appears analogous to what is observed in cyanobacteria. We postulate that expansion of the ncHLI gene family and its regulation may reflect the light/oxidative stress experienced by Paulinella chromatophora as a consequence of the as yet incomplete integration of host and chromatophore metabolisms.

Light Intensity and Light Quality from Sole-source Light-emitting Diodes Impact Phytochemical Concentrations within Brassica Microgreens

Multilayer vertical production systems using sole-source (SS) light-emitting diodes (LEDs) can be an alternative to more traditional methods of microgreens production. One significant benefit of using LEDs is the ability to select light qualities that have beneficial impacts on plant morphology and the synthesis of health-promoting phytochemicals. Therefore, the objective of this study was to quantify the impacts of SS LEDs of different light qualities and intensities on the phytochemical content of brassica (Brassica sp.) microgreens. Specifically, phytochemical measurements included 1) total anthocyanins, 2) total and individual carotenoids, 3) total and individual chlorophylls, and 4) total phenolics. Kohlrabi (Brassica oleracea var. gongylodes), mustard (Brassica juncea ‘Garnet Giant’), and mizuna (Brassica rapa var. japonica) were grown in hydroponic tray systems placed on multilayer shelves in a walk-in growth chamber. A daily light integral (DLI) of 6, 12, or 18 mol·m−2·d−1 was achieved from SS LED arrays with light ratios (percent) of red:blue 87:13 (R87:B13), red:far-red:blue 84:7:9 (R84:FR7:B9), or red:green:blue 74:18:8 (R74:G18:B8) with a total photon flux from 400 to 800 nm of 105, 210, or 315 µmol·m−2·s–1 for 16 hours, respectively. Phytochemical measurements were collected using spectrophotometry and high-performance liquid chromatography (HPLC). Regardless of light quality, total carotenoids were significantly lower under increasing light intensities for mizuna and mustard microgreens. In addition, light quality affected total integrated chlorophyll with higher values observed under the light ratio of R87:B13 compared with R84:FR7:B9 and R74:G18:B8 for kohlrabi and mustard microgreens, respectively. For kohlrabi, with increasing light intensities, the total concentration of anthocyanins was greater compared with those grown under lower light intensities. In addition, for kohlrabi, the light ratios of R87:B13 or R84:FR7:B9 produced significantly higher anthocyanin concentrations compared with the light ratio of R74:G18:B8 under a light intensity of 315 µmol·m−2·s−1. Light quality also influenced the total phenolic concentration of kohlrabi microgreens, with significantly greater levels for the light ratio of R84:FR7:B9 compared with R74:G18:B8 under a light intensity of 105 µmol·m−2·s−1. However, the impact of light intensity on total phenolic concentration of kohlrabi was not significant. The results from this study provide further insight into the selection of light qualities and intensities using SS LEDs to achieve preferred phytochemical content of brassica microgreens.

Light Intensity Is a Main Factor Affecting Fresh Market Spinach Tolerance for Phenmedipham

The few available herbicides for fresh market spinach do not provide adequate weed control, and there is need for additional herbicide tools. Phenmedipham is registered for use in processing spinach but not in fresh spinach, because of potential injury and the short interval between application and spinach harvest. The objectives of this study were to evaluate the tolerance level of fresh spinach varieties to phenmedipham and evaluate the impact of light intensity on tolerance of spinach to phenmedipham. In the greenhouse, nine spinach varieties were treated with phenmedipham (0.55 kg ai ha−1). Spinach varieties exhibited a wide range of tolerance, and dry weights of treated plants ranged from 40 to 78% compared to the nontreated control. Based on the phenmedipham tolerance screen, two varieties with low (Nordic) and high (Regal) tolerance to phenmedipham were treated, then exposed to half (shaded) and full (nonshaded) sunlight. Nonshaded Nordic treated with phenmedipham had 65% lower dry weight compared to similarly treated plants grown under shade, suggesting that spinach tolerance to phenmedipham was mainly affected by light intensity. Measurements of electron transfer intensity in photosystem II also showed tolerance to phenmedipham that varied among spinach varieties and light intensity. The maximum values of electron transfer in photosystem II of Regal treated with phenmedipham were higher than those of similarly treated Nordic. In the field, phenmedipham was applied under varied light and temperature conditions. The impact of light intensity on yield of treated spinach was greater than the impact of temperature. Phenmedipham applied under high light conditions was more injurious than when applied under low light conditions. Results from this study can contribute to successful integration of phenmedipham into currently used fresh spinach weed management, which in turn can allow more efficient production of this crop.

Impact of light intensity on the polymerization kinetics and network structure of model hydrophobic and hydrophilic methacrylate based dental adhesive resin.

The impact of light intensity on the degree of conversion (DC), rate of polymerization and network structure was investigated for hydrophobic and hydrophilic dental adhesive resins. Two and three component photoinitiating (PI) systems were used in this study. Low light intensities had a negative impact on the polymerization efficiency for the hydrophilic resin with 2 component PI system. Incorporation of iodonium salt in the hydrophilic resin significantly improved the polymerization efficiency of the HEMA/BisGMA system and led to a substantial DC, even at low light intensities. The results suggested that shorter polymer chains were formed in the presence of iodonium salt. It appears that there is little or no impact of light intensity on the polymer structure of the 2 component PI system. Light intensity has subtle impact on the polymer structure of the 3 component PI system. In the case of the hydrophobic resin, the polymer is so highly cross-linked that the presence of shorter chains for the 3 component PI system does not cause a decrease in the glass transition temperature (Tg ) when compared to the 2 component PI system. For the hydrophilic resin, the presence of shorter polymer chains in the 3 component PI system reduces the Tg when compared with the corresponding 2 component PI system. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 104B: 1666-1678, 2016.

Algal productivity modeling: a step toward accurate assessments of full-scale algal cultivation.

A new biomass productivity model was parameterized for Chlorella vulgaris using short-term (<30 min) oxygen productivities from algal microcosms exposed to 6 light intensities (20-420 W/m(2)) and 6 temperatures (5-42 °C). The model was then validated against experimental biomass productivities recorded in bench-scale photobioreactors operated under 4 light intensities (30.6-74.3 W/m(2)) and 4 temperatures (10-30 °C), yielding an accuracy of ± 15% over 163 days of cultivation. This modeling approach addresses major challenges associated with the accurate prediction of algal productivity at full-scale. Firstly, while most prior modeling approaches have only considered the impact of light intensity on algal productivity, the model herein validated also accounts for the critical impact of temperature. Secondly, this study validates a theoretical approach to convert short-term oxygen productivities into long-term biomass productivities. Thirdly, the experimental methodology used has the practical advantage of only requiring one day of experimental work for complete model parameterization. The validation of this new modeling approach is therefore an important step for refining feasibility assessments of algae biotechnologies.

Effect of light intensity, pH, and temperature on triacylglycerol (TAG) accumulation induced by nitrogen starvation in Scenedesmus obliquus

Microalgae-derived lipids in the form of triacylglycerols (TAGs) are considered an alternative resource for the production of biofuels and food commodities. Large scale production of microalgal TAGs is currently uneconomical. The cost price could be reduced by improving the areal and volumetric TAG productivity. The economic value could be increased by enhancing the TAG quality. To improve these characteristics, the impact of light intensity, and the combined impact of pH and temperature on TAG accumulation were studied for Scenedesmus obliquus UTEX 393 under nitrogen starved conditions. The maximum TAG content was independent of light intensity, but varied between 18% and 40% of dry weight for different combinations of pH and temperature. The highest yield of fatty acids on light (0.263 g/mol photon) was achieved at the lowest light intensity, pH 7 and 27.5 °C.

Interactions of Light Intensity, Insecticide Concentration, and Time on the Efficacy of Systemic Insecticides in Suppressing Populations of the Sweetpotato Whitefly (Hemiptera: Aleyrodidae) and the Citrus Mealybug (Hemiptera: Pseudococcidae)

The impact of light intensity on the uptake and persistence of the systemic neonicotinoid insecticides, imidacloprid and dinotefuran, were evaluated in poinsettia (Euphorbia pulcherrima Willd.) and yellow sage (Lantana camara L.). Insecticide residues were measured in leaves sampled from the treated plants at four time intervals after treatment to determine the relationship between insecticide concentration and efficacy against two insect pests: sweetpotato whitefly, Bemisia tabaci Gennadius, and the citrus mealybug, Planococcus citri Risso. The insecticides were evaluated at their respective label rate and at the comparable label rate of the other insecticide under two different light environments: ambient and shade. The uptake of dinotefuran into yellow sage was more rapid at both treatment rates than both rates of imidacloprid, resulting in higher percent mortality of whitefly nymphs (89.8-100) compared with imidacloprid (14.1-89.2) across all 4 wk. Additionally, plants that received both rates of dinotefuran had fewer whitefly pupae (< 1.0) at week 4 compared with imidacloprid-treated plants (23.7-25.3). The uptake of dinotefuran into poinsettia plants was also more rapid and resulted in quicker and higher percent mortality of whitefly nymphs (89.5-99.6) compared with imidacloprid (14.1-89.2) across all 4 wk. However, despite efficient uptake, the efficacy of both systemic insecticides was less for citrus mealybug where percent mortality values were <50% among all the treatments across the 4 wk. The use of the two systemic insecticides evaluated in regards to pest management in horticultural cropping systems is discussed.

The impact of light intensity on shade‐induced leaf senescence

Plants often have to cope with altered light conditions, which in leaves induce various physiological responses ranging from photosynthetic acclimation to leaf senescence. However, our knowledge of the regulatory pathways by which shade and darkness induce leaf senescence remains incomplete. To determine to what extent reduced light intensities regulate the induction of leaf senescence, we performed a functional comparison between Arabidopsis leaves subjected to a range of shading treatments. Individually covered leaves, which remained attached to the plant, were compared with respect to chlorophyll, protein, histology, expression of senescence-associated genes, capacity for photosynthesis and respiration, and light compensation point (LCP). Mild shading induced photosynthetic acclimation and resource partitioning, which, together with a decreased respiration, lowered the LCP. Leaf senescence was induced only under strong shade, coinciding with a negative carbon balance and independent of the red/far-red ratio. Interestingly, while senescence was significantly delayed at very low light compared with darkness, phytochrome A mutant plants showed enhanced chlorophyll degradation under all shading treatments except complete darkness. Taken together, our results suggest that the induction of leaf senescence during shading depends on the efficiency of carbon fixation, which in turn appears to be modulated via light receptors such as phytochrome A.

Impact of Light Intensity on Biosynthesis of Active Ingredients in Epimedium

As a traditional Chinese medicinal herb,epimedii has effects on toning kidney,strengthening bones and muscles,and treating rheumatism.Its bioactive ingredients are mainly prenylated flavonol glycosides,including icariin,epimedin A,B,and C.Two light conditions [Yao-yuan(Medicinal Herb Garden) of Wuhan Botanical Garden,Yuan-wai-yuan of Wuhan Botanical Garden] were used to study how light affected the biosynthesis of the major bioactive ingredients in Epimedium wushanense T.S.Ying and Epimedium sagittatum(Sieb. Zucc.) Maxim.Results showed that the photosynthesis rate was higher in Yao-yuan than in Yuan-wai-yuan for both species.The four bioactive ingredients of E.sagittatum were higher in Yao-yuan than in Yuan-wai-yuan,but the opposite was found for E.wushanense.Photosynthesis rate had significant positive correlation with the content of epimedin A,B and icariin,but had significant negative correlation with epimedin C.The relationship between photosynthesis rate and accumulation of bioactive ingredients was discussed.Suggestions were also proposed for cultivating different Epimedium species.

Impact of light intensity on the results of rearing juvenile pikeperch, Sander lucioperca (L.), in recirculating aquaculture systems

The aim of the study was to determine the impact of different light intensities on the results of rearing juvenile pikeperch, Sander lucioperca (L.), in recirculating aquaculture systems (RAS). In experiment I, the light intensities applied were 45.1 lx (group LI) and 385.7 lx (group HI) (initial body weight - 6.1 g), while in experiment II they were 1.2 lx (group LII) and 8.0 lx (group HII) (initial body weight - 42.2 g). In both experiments, the fish reared in the tanks with lower light intensity (groups LI and LII) exhibited faster growth rates (P 0.05). The results obtained indicate that the application of low intensity light ( 6 g) rearing is justified since it has a positive impact on the behavior and growth rate of the fish, and the feed conversion ratio, which implies that it is possible to shorten the rearing period of this species.

Light preferences of red swamp crayfish (Procambarus clarkii)

Light intensity preferences of Procambarus clarkii (Girard, 1852) were evaluated in an indoor fiber glass trough, consisting of five equal length (4 m) zones with light intensities varying from dark to 1,000 lux (L), situated at the ‘Las Vegas del Guadiana’ fish farm in Extremadura (Spain). Four trials were performed, with different light zones set in three at sections of the trough, and the fourth providing a control with one light density (300 L) throughout the trough. Whereas the highest intensity (1,000 L) was preferred in trials 1 and 2, the dimmest condition (D) was favored in trial 3. Crayfish showed a strong preference to both outside ends of the trough, and the “end effect” of the trough on position of the crayfish was found to be stronger than the impact of light intensity.

Kinetic Study of Application of ZnO as a Photocatalyst in Heterogeneous Medium

The photocatalytic degradation of 2,4‐dinitrophenol over ZnO was carried out in the presence of light. Control experiments were carried out. The photocatalytic degradation of 2,4‐dinitrophenol was observed spectro‐photmerically. The various parameters like concentrations of substrate, pH, amounts and band gaps of semiconductor, impact of light intensity, sensitizers and radical quenchers affected the kinetics of the degradation process. A probable mechanism for this process has been proposed.

Morphometry and growth of three Synechococcus-like picoplanktic cyanobacteria at different culture conditions

Three phycocyanin-rich strains of Synechococcus-like picoplanktic cyanobacteria, isolated from the plankton of Czech oligotrophic to eutrophic freshwater reservoirs, were investigated in crossed gradients of light and temperature and in combination with two different culture media (BG-11 and WC). The strains exhibited similar growth and reproduction patterns and displayed overlapping ranges of cell size (1.5 × 0.8 μm) under standardized laboratory conditions (18 μmol m−2 s−1; 20°C). However, strains behavior differed in the crossed gradients. All strains preferred BG-11 medium, where also remarkable size changes could be observed. Length, width, cell abundance and growth rate of two strains were positively correlated with temperature and nutrients, whereas the impact of light intensity was insignificant. Maximum cell elongation (involution cells up to 19 μm) occurred in two strains only in BG-11 medium at highest temperature (28°C) and highest irradiance (53 μmol m−2 s−1). Cell dimensions in WC medium were constant under most conditions given. The third strain was influenced by all three factors, from which light and nutrients played pivotal role. The length of the lag-phase for all strains appeared to be temperature dependent (negative correlation). Despite the fact that the cell volume in all strains increased more than five times under the lowest light and low temperature (6 μmol m−2 s−1, <15°C) in both media, the length/width ratio remained unchanged. The strains differed in the degree of cell enlargement and cell division symmetry as well as in optimum temperature and light dependence. Based on this experimental work two strains could be identified as Synechococcus sp. and one as Cyanobium sp., which can be used as a support for the following genetical analyses.

The impact of light intensity and algal-induced turbidity on first-feeding Seriola lalandi larvae

Feeding performance (intensity and incidence) of first-feeding yellowtail kingfish larvae was evaluated under a range of light intensities and algal-induced turbidities. Larvae were fed with varying degrees of success under all light intensities tested (0–17 μmol s−1 m−2), in both clearwater and greenwater (8 × 104 cells mL−1). There was a consistent trend for feeding performance to increase with larval age and light intensity in both clearwater and greenwater conditions, demonstrating that visual proficiency increases with larval age. Feeding intensity remained low over the first 3 days of first feeding across all light intensities tested. Days 6 and 7 post-hatch larvae showed considerably higher feeding intensities particularly at 8 and 17 μmol s−1 m−2. This improvement indicates an ontogenetic shift in sensory or locomotor competence. First-feeding larvae performed equally well in both clearwater and greenwater (8 × 104 cells mL−1) conditions, although at the lowest light intensity tested (0.1 μmol s−1 m−2) feeding performance was noticeably reduced. Feeding performance was severely diminished across all larval ages at an algal cell density of 32 × 104 cells mL−1, demonstrating that for this species algal-induced turbidities >16 × 104 cells mL−1 adversely affect the ability to capture free-swimming prey during the first-feeding window.

An Investigation of Chain Length Dependent Termination and Reaction Diffusion Controlled Termination during the Free Radical Photopolymerization of Multivinyl Monomers

Recent investigations of dimethacrylate monomers reveal that chain length dependent termination (CLDT) is important during network formation; however, the importance is not a trivial function of double bond conversion or monomer chemistry. Poly(ethylene glycol)-600 dimethacrylate (PEG600DMA) simultaneously exhibits CLDT and reaction diffusion controlled termination and a reaction diffusion coefficient that depends on the cure condition. To investigate this behavior, the impact of light intensity, monomer chemistry, and network formation on the termination mechanism was investigated. The copolymerization of PEG600DMA with increasing di(ethylene glycol) dimethacrylate (DEGDMA) concentrations reveals that the importance of CLDT during reaction diffusion controlled termination is a function of the rubbery or glassy nature of the resulting polymer network. As well, the addition of nonreactive PEG600 to the DEGDMA polymerization increases the importance of CLDT throughout the polymerization and elevates the rea...

Understanding multivinyl monomer photopolymerization kinetics through modeling and GPC investigation of degradable networks

Multivinyl monomers that react to form highly crosslinked, biodegradable networks are being developed as scaffolds for tissue engineering and vehicles for drug delivery; however, this work demonstrates their usefulness in characterizing better the complexities of the kinetics and structural evolution during crosslinking photopolymerization. The molecular weight distributions (MWDs) of the degradation products of networks formed through the free radical photopolymerization of multivinyl monomers validate a novel kinetic model to test hypotheses as to the important kinetic mechanisms during crosslinking. The kinetic model, in conjunction with the experimental results for the degradable network, provides insight into the fundamental termination mechanisms (i.e. chain length dependent termination (CLDT), chain transfer to either a unimolecular species or polymer, and the accumulation of persistent radicals) that control the MWD of the backbone kinetic chains throughout the polymerization. Specifically, the importance of CLDT during autoacceleration and the impact of light intensity on the MWD of the backbone kinetic chains are presented.

Impact of light intensity on flowering time and plant quality of Antirrhinum majus L. cultivar Chimes White.

Shades of different light intensities (29%, 43%, 54%, 60% or 68%) along with control (no shade) were studied to observe their effects on the flowering time and plant quality. A hyperbolic relationship was observed between different light intensities under shade, and time to flowering. The total number of flower buds showed a curvilinear relationship with light intensities. Growth parameters related to the plant characteristics such as plant height, leaf area and plant fresh weight were improved under shading treatments at the expense of flowering time and number of flower buds. However, both linear and polynomial models applied assumed that cultivar Chimes White was equally sensitive to light intensity throughout development.

The impact of light intensity and daylength on silicate and nitrate competition among marine phytoplankton

I tested the extent to which differences in light supply could influence the outcome of nutrient (Si and N) competition between marine phytoplankton. Competition experiments were performed with 11 species of marine phytoplankton at Si: N ratios from 16 to 124 : 1, light intensities from 28 to 225 µmol quanta m−2 s−1, and three different daylengths. Thus, light supply was the composite result of two components: photoperiod and intensity. Diatoms were dominant competitors at higher Si: N ratios, nonsiliceous flagellates at lower ones. Light had no impact on the transition from flagellate to diatom dominance along the Si: N gradient. However, species within those groups were separated along the light gradient. Contrary to theoretical expectations, changes in light intensity and changes in daylength led to similar shifts in species dominance. Therefore, it was possible to describe the light climate by the integral parameter “daily light dose.”