Spectral Distribution Of Light Research Articles

(INVITED) Recent progress on broadband near-infrared phosphors-converted light emitting diodes for future miniature spectrometers

The development of phosphor-converted technology-based broadband near-infrared light source for miniature spectrometers to perform spectroscopy applications has recently attracted remarkable attention among researchers in the academe and industry. The transition metal element Cr3+-activated luminescent materials act as the potential candidates to meet the demands for increased near-infrared light spectral distribution. In this mini-review, the most recently developed broadband near-infrared phosphors activated by Cr3+ are listed and classified according to their major chemical element constituents. In addition to the luminescence mechanism of Cr3+, the association between the number of crystallographic sites and spectral distribution of near-infrared light is mainly reviewed with the example of known near-infrared phosphors, which may be helpful in exploring future broadband near-infrared phosphors. Finally, the performance-evaluating parameters of phosphor-converted near-infrared light-emitting diode are discussed and compared with those of known broadband near-infrared phosphors for spectroscopy applications.

Color Engineering of Silicon Nitride Surfaces to Characterize the Polydopamine Refractive Index.

A simple methodology to generate polydopamine (PDA) surfaces featured with color due to thin-film interference phenomena is presented. It is based on depositing ultra-thin films of polydopamine on a Si/Si3 N4 wafer that exhibits an interferential reflectance maximum right at the visible/UV boundary (∼400 nm). Therefore, a small deposit of PDA modifies the optical path, in such manner that the wavelength of the maximum of reflectance red shifts. Because the human eye is very sensitive to any change of the light spectral distribution at the visible region, very small film thickness changes (∼30 nm) are enough to notably modify the perceived color. Consequently, a controlled deposit of PDA, tune the color along the whole visible spectrum. Additionally, good quality of PDA deposits allowed us to determine the refractive index of polydopamine by ellipsometry spectroscopy. This data can be crucial in confocal skin microscopic techniques, presently used in diagnosis of skin tumors.

Detection of the blazar S4 0954+65 at very-high-energy with the MAGIC telescopes during an exceptionally high optical state

Aims. The very high energy (VHE ≳100 GeV) γ-ray MAGIC observations of the blazar S4 0954+65, were triggered by an exceptionally high flux state of emission in the optical. This blazar has a disputed redshift of z = 0.368 or z ≥ 0.45 and an uncertain classification among blazar subclasses. The exceptional source state described here makes for an excellent opportunity to understand physical processes in the jet of S4 0954+65 and thus contribute to its classification. Methods. We investigated the multiwavelength (MWL) light curve and spectral energy distribution (SED) of the S4 0954+65 blazar during an enhanced state in February 2015 and have put it in context with possible emission scenarios. We collected photometric data in radio, optical, X-ray, and γ-ray. We studied both the optical polarization and the inner parsec-scale jet behavior with 43 GHz data. Results. Observations with the MAGIC telescopes led to the first detection of S4 0954+65 at VHE. Simultaneous data with Fermi-LAT at high energy γ-ray (HE, 100 MeV < E < 100 GeV) also show a period of increased activity. Imaging at 43 GHz reveals the emergence of a new feature in the radio jet in coincidence with the VHE flare. Simultaneous monitoring of the optical polarization angle reveals a rotation of approximately 100°. Conclusions. The high emission state during the flare allows us to compile the simultaneous broadband SED and to characterize it in the scope of blazar jet emission models. The broadband spectrum can be modeled with an emission mechanism commonly invoked for flat spectrum radio quasars (FSRQs), that is, inverse Compton scattering on an external soft photon fieldfrom the dust torus, also known as external Compton. The light curve and SED phenomenology is consistent with an interpretation of a blob propagating through a helical structured magnetic field and eventually crossing a standing shock in the jet, a scenario typically applied to FSRQs and low-frequency peaked BL Lac objects (LBL).

A Mathematical Model of Photosynthetic Electron Transport in Response to the Light Spectrum Based on Excitation Energy Distributed to Photosystems.

To enable us to analyze more systematically the effects of the spectral distribution of light (i.e. light quality) on photosynthetic electron transport, we propose a simple mathematical model which describes electron transport reactions under light-limited conditions based on the excitation energy distributed to the photosystems. The model assumes that the rate-limiting photosystem performs the photochemical reaction at its maximum yield, while the yield in the other photosystem is passively down-regulated to equalize the rates of linear electron transport through the photosystems. Using intact cucumber leaves, we tested the model by comparing actual and estimated photosynthetic parameters under several combinations of photon flux densities of red and far-red lights (R and FR, respectively). Simultaneously provided R and FR yielded greater gross photosynthetic rates than the sums of the rates under only R and only FR, which is known as the 'enhancement effect'. The present model reproduced these non-additive increases in the gross photosynthetic rates in response to supplemental FR to R and provided more accurate estimates than an existing method that did not take the enhancement effect into account (root mean square errors: 0.11 and 0.21 μmol m-2 s-1, respectively). Using the present model, the photon flux density of the supplemental FR which gives the changing point of rate-limiting photosystem and the photochemical yields of the non-rate-limiting photosystems were estimated reasonably well. The present study has therefore formulated a simplified quantitative electron transport model in response to the light spectrum based on generally accepted concepts and demonstrated its validity experimentally.

Signals of Systemic Immunity in Plants: Progress and Open Questions.

Systemic acquired resistance (SAR) is a defence mechanism that induces protection against a wide range of pathogens in distant, pathogen-free parts of plants after a primary inoculation. Multiple mobile compounds were identified as putative SAR signals or important factors for influencing movement of SAR signalling elements in Arabidopsis and tobacco. These include compounds with very different chemical structures like lipid transfer protein DIR1 (DEFECTIVE IN INDUCED RESISTANCE1), methyl salicylate (MeSA), dehydroabietinal (DA), azelaic acid (AzA), glycerol-3-phosphate dependent factor (G3P) and the lysine catabolite pipecolic acid (Pip). Genetic studies with different SAR-deficient mutants and silenced lines support the idea that some of these compounds (MeSA, DIR1 and G3P) are activated only when SAR is induced in darkness. In addition, although AzA doubled in phloem exudate of tobacco mosaic virus (TMV) infected tobacco leaves, external AzA treatment could not induce resistance neither to viral nor bacterial pathogens, independent of light conditions. Besides light intensity and timing of light exposition after primary inoculation, spectral distribution of light could also influence the SAR induction capacity. Recent data indicated that TMV and CMV (cucumber mosaic virus) infection in tobacco, like bacteria in Arabidopsis, caused massive accumulation of Pip. Treatment of tobacco leaves with Pip in the light, caused a drastic and significant local and systemic decrease in lesion size of TMV infection. Moreover, two very recent papers, added in proof, demonstrated the role of FMO1 (FLAVIN-DEPENDENT-MONOOXYGENASE1) in conversion of Pip to N-hydroxypipecolic acid (NHP). NHP systemically accumulates after microbial attack and acts as a potent inducer of plant immunity to bacterial and oomycete pathogens in Arabidopsis. These results argue for the pivotal role of Pip and NHP as an important signal compound of SAR response in different plants against different pathogens.

Impact of the spectral and spatial properties of natural light on indoor gas-phase chemistry: Experimental and modeling study.

The characteristics of indoor light (intensity, spectral, spatial distribution) originating from outdoors have been studied using experimental and modeling tools. They are influenced by many parameters such as building location, meteorological conditions, and the type of window. They have a direct impact on indoor air quality through a change in chemical processes by varying the photolysis rates of indoor pollutants. Transmittances of different windows have been measured and exhibit different wavelength cutoffs, thus influencing the potential of different species to be photolysed. The spectral distribution of light entering indoors through the windows was measured under different conditions and was found to be weakly dependent on the time of day for indirect cloudy, direct sunshine, partly cloudy conditions contrary to the light intensity, in agreement with calculations of the transmittance as a function of the zenithal angle and the calculated outdoor spectral distribution. The same conclusion can be drawn concerning the position within the room. The impact of these light characteristics on the indoor chemistry has been studied using the INCA-Indoor model by considering the variation in the photolysis rates of key indoor species. Depending on the conditions, photolysis processes can lead to a significant production of radicals and secondary species.

Influence of spectral distribution on accommodation—vergence and reading performance

Background: To assess the influence of different spectral energy distribution on accommodation, vergence and reading performance. Methods: A Randomized experimental study was conducted after getting the approval of the Ethical Committee of University of Hyderabad. Forty participants with an age group of 18–21 years was integrated, out of which 50% was male and 50% was female. Subjects with emmetropia and no history of ocular pathology were included in the study. Near point of accommodation (NPA) & near point of convergence (NPC) was measured with the help of royal air force (RAF) ruler followed by near visual task of a readability passage. Results: A statistically significant result was obtained when reading rate, reading speed and NPC was compared among different spectral distribution of light (P Conclusions: This study concluded that reading performance (reading rate and reading speed) and NPC has a significance change if we use inappropriate lighting during visual tasks. It will cause visual fatigue and strain after sustained near work. In addition, tungsten spectral energy influences the convergence which can also show an impact on reading and near visual tasks because of its brightness and miosis. Prolonged reading and working under this lighting can cause convergence disorders and visual fatigue.

Appraising the intention of other people: Ecological validity and procedures for investigating effects of lighting for pedestrians

One of the aims of outdoor lighting in public spaces, such as pathways and subsidiary roads, is to help pedestrians to evaluate the intentions of other people. This paper discusses how a pedestrians' appraisal of another persons' intentions in artificially lit outdoor environments can be studied. We review the visual cues that might be used, and the experimental design with which effects of changes in lighting could be investigated to best resemble the pedestrian experience in artificially lit urban environments. Proposals are made to establish appropriate operationalisation of the identified visual cues, choice of methods and measurements representing critical situations. It is concluded that the intentions of other people should be evaluated using facial emotion recognition; eye-tracking data suggest a tendency to make these observations at an interpersonal distance of 15 m and for a duration of 500 ms. Photographs are considered suitable for evaluating the effect of changes in light level and spectral power distribution. To support investigation of changes in spatial distribution, further investigation is needed with three-dimensional targets. Further data are also required to examine the influence of glare.

Lighting efficiency under mesopic photometry conditions

The influence of spectral light distribution of light sources on effectivity of road lighting systems in twilight conditions photometry was considered in the paper. An experiment was carried out to investigate different spectral power distributions. One aim was to verify that S/P increases with increasing color temperature. Next aim was to clarify situation with the need to reviewing the actual lighting norms in Ukraine considering the results of researches indicates that light with a higher scotopic/photopic (S/P) ratio would be more effective in street lighting systems as they would be perceived as brighter at the same power.

Reducing shade avoidance responses in a cereal crop.

Several researchers have hypothesized that shade avoidance behaviour is favoured by natural selection because it increases the fitness of individuals. Shade avoidance can be disadvantageous for crops, however, because it reduces allocation of resources to reproductive yield, increases the risk of lodging and reduces weed suppression. One approach to develop varieties with reduced shade avoidance and enhanced agronomic performance is by inducing mutations followed by phenotypic screening. We treated spring wheat seeds with ethyl methanesulfonate and screened the seedlings repeatedly under green filters for plants showing reduced elongation of the first leaf sheath and second leaf lamina. The shade avoidance responses of five promising mutant lines were further compared to non-mutated plants in a climate chamber experiment with added far-red light. Two of the selected lines displayed significantly reduced elongation under all light treatments while two lines showed reduced elongation only in added far-red light. The most promising mutant line did not differ in height from the non-mutated cultivar in neutral light, but elongated 20.6% less in strong far-red light. This traditional forward approach of screening mutagenized spring wheat produced plants with reduced shade avoidance responses. These mutants may generate new molecular handles to modify the reaction of plants to changes in light spectral distribution in traditional and novel cultivation systems.

Spectral distribution of light under different structures and cover materials employed in Mediterranean greenhouses

Light quality is related with the intensity of photosynthetic active radiation (PAR) received by the crop, but the spectral distribution of light can also influence the plant development (photomorphogenesis) and some plant physiologists have defined the concept of morphogenetically active radiation (MAR). In Mediterranean areas, ornamental crops, especially in summer conditions, are cultivated under different structural typologies and, also, in the open air. The aim of this work is to characterize and evaluate the quality of the radiation recording the different bands of the light spectrum affecting crop production, offered by different structures and cover materials employed in Mediterranean greenhouses. The spectrum regions studied were the following: ultraviolet UV (300-400 nm), blue B (400-500 nm), red R (600-700 nm), far red FR (700-800 nm), PAR (400-700 nm), near infrared NIR (700-1100 nm) and Global (GR) (300-1100 nm). The results show how structures modify the global radiation transmission uniformly through the spectrum, apart from the case of the UV band where the “Parral” greenhouse (PG) transmission is lower. The use of aluminised screen reduces the global radiation in the greenhouse, but this reduction is not homogeneous in the different bands where UV and B bands present the highest reduction. The ratios PAR/NIR; B/R; B/FR and R/FR were higher without aluminised screen. The use of anti-pest mesh supposes a loss of radiation received by the crop and it is more noticeable in the UV and B bands with around 30% of reduction.

Response of greenhouse tomato to different vertical spectra of LED lighting under overhead high pressure sodium and plasma lighting

Different light spectra trigger different plant growth processes. Therefore, the optimum light spectrum for various plant growth processes such as leaf and fruit growth may be different. Greenhouse mini-cucumber (Cucumis sativus L.) is a tall crop, with most leaf growth occurring in the top and middle canopy while fruit growth occurs in the middle and bottom canopy. Therefore, optimized vertical light spectral distribution profiles could be developed for improving both vegetative and fruit growth. In this study, we investigated the effects of different vertical spectra of light-emitting diodes (LED) lighting under high-pressure sodium (HPS) and plasma overhead lighting on plant growth and fruit yield of mini-cucumber. The study was conducted from October 2014 to April 2015 in a large greenhouse divided into 4 sections (50 m2 growing area in each section). Two sections were installed with plasma overhead light and the other two sections with HPS light, with both of them providing the same amount of overhead light (165 μmol m-2 s-1). Four vertical LED regimes (the top far red with bottom blue; the top blue with bottom far red; the top far red with bottom red; the top red with bottom far red) were applied to 4 plots inside each of the 4 sections. The blue or red LED each provided 10 µmol m-2 s-1, while the far red LED provided 8 µmol m-2 s-1 of light. The vertical LED treatments resulted in more than a 10% difference in fruit yield despite the small amount of light, indicating that the vertical light distribution had a large influence on plant growth. Top blue LED reduced leaf size and plant height in the early growth period which reduced total fruit yield for the plants grown under plasma light but not under HPS. Far red LED placed at the top of the canopy increased fruit yield, in comparison to bottom canopy placement, for plants grown under plasma light. This study has demonstrated that vertical light spectral distribution can have a large influence on plant growth and development, and optimized light distribution should and can be developed for year-round greenhouse vegetable production with supplemental lighting.

Scanning tunnelling microscope light emission: Finite temperature current noise and over cut-off emission

The spectral distribution of light emitted from a scanning tunnelling microscope junction not only bears its intrinsic plasmonic signature but is also imprinted with the characteristics of optical frequency fluc- tuations of the tunnel current. Experimental spectra from gold-gold tunnel junctions are presented that show a strong bias (Vb) dependence, curiously with emission at energies higher than the quantum cut-off (eVb); a component that decays monotonically with increasing bias. The spectral evolution is explained by developing a theoretical model for the power spectral density of tunnel current fluctuations, incorporating finite temperature contribution through consideration of the quantum transport in the system. Notably, the observed decay of the over cut-off emission is found to be critically associated with, and well explained in terms of the variation in junction conductance with Vb. The investigation highlights the scope of plasmon-mediated light emission as a unique probe of high frequency fluctuations in electronic systems that are fundamental to the electrical generation and control of plasmons.

The spectral power distribution of light and twilight photometry

The influence of spectral light distribution of light sources for visibility in twilight conditions photometry is considered. Study of this subject is analyzed. The calculations of S/P ratio of samples of the lights of the leading Ukrainian companies and recommendations as for improvement of the efficiency of lighting conditions for driving conditions in twilight time are submitted.

Light distribution and spectral composition within cultures of micro-algae: Quantitative modelling of the light field in photobioreactors

Light, being the fundamental energy source to sustain life on Earth, is the external factor with the strongest impact on photosynthetic microorganisms. Moreover, when considering biotechnological applications such as the production of energy carriers and commodities in photobioreactors, light supply within the reactor volume is one of the main limiting factors for an efficient system. Thus, the prediction of light availability and its spectral distribution is of fundamental importance for the productivity of photo-biological processes.The light field model here presented is able to predict the intensity and spectral distribution of light throughout the reactor volume based on the incident light and the spectral characteristics of the photosynthetic microorganism. It takes into account the scattering and absorption behaviour of the micro-algae, as well the adaptation of the biological system to different light intensities.Although in the form exposed here the model is optimized for photosynthetic microorganism cultures inside flat- type photobioreactors, the theoretical framework is easily extensible to other geometries. Our calculation scheme has been applied to model the light field inside Synechocystis sp. PCC 6803 wild-type and Olive antenna mutant cultures at different cell-density concentrations exposed to white, blue, green and red LED lamps, delivering results with reasonable accuracy, despite the data uncertainties. To achieve this, Synechocystis experimental attenuation profiles for different light sources were estimated by means of the Beer-Lambert law, whereby the corresponding downward irradiance attenuation coefficients Kd(λ) were obtained through inherent optical properties of each organism at any wavelength within the photosynthetically active radiation band. The input data for the algorithm are chlorophyll-specific absorption and scattering spectra at different mean acclimatisation irradiance values for a given organism, the depth of the photobioreactor, the cell-density and also the intensity and emission spectrum of the light source.In summary, the model is a general tool to predict light availability inside photosynthetic microorganism cultures and to optimize light supply, in respect to both intensity and spectral distribution, in technological applications. This knowledge is crucial for industrial-scale optimisation of light distribution within photobioreactors and is also a fundamental parameter for unravelling the nature of many photosynthetic processes.

A Basis for Selecting Light Spectral Distribution for Evaluating Leaf Photosynthetic Rates of Plants Grown under Different Light Spectral Distributions

A Basis for Selecting Light Spectral Distribution for Evaluating Leaf Photosynthetic Rates of Plants Grown under Different Light Spectral Distributions

On the induction of injury in tomato under continuous light: circadian asynchrony as the main triggering factor.

Unlike other species, when tomato plants (Solanum lycopersicum L.) are deprived of at least 8h of darkness per day, they develop a potentially lethal injury. In an effort to understand why continuous light (CL) is injurious to tomato, we tested five factors, which potentially could be responsible for triggering the injury in CL-grown tomato: (i) differences in the light spectral distribution between sunlight and artificial light, (ii) continuous light signalling, (iii) continuous supply of light for photosynthesis, (iv) continuous photo-oxidative pressure and (v) circadian asynchrony - a mismatch between the internal circadian clock frequency and the external light/dark cycles. Our results strongly suggest that continuous-light-induced injury does not result from the unnatural spectral distribution of artificial light nor from the continuity of light per se. Instead, circadian asynchrony seems to be the main factor inducing the CL-induced injury, but the mechanism is not by the earlier hypothesised circadian pattern in sensitivity for photoinhibition. Here, however, we show for the first time diurnal fluctuations in sensitivity to photoinhibition during normal photoperiods. Similarly, we also report for the first time diurnal and circadian rhythms in the maximum quantum efficiency of PSII (Fv/Fm) and the parameter F0.

The Influence of Internal Coloured Surfaces on the Circadian Efficiency of Indoor Daylight

The discovery of circadian stimulation by daylight has changed our understanding of the important effect the daylight has on our health and wellbeing. The new medical facts that emerged during the last decade have proven that a long-term absence of circadian light stimulation may be associated with sleep disturbance, tiredness and increased incidence of chronic depression, bipolar disorder, and seasonal affective disorder. The reason is the difference between the visual and biological (circadian) response to light and how it is being perceived by human beings: while the visual perception represented by the luminous efficiency function peaks at the wavelength of 555 nm, the circadian photoreception curve peaks in the blue light spectrum at ~450 nm. The primary circadian stimulation by daylight depends on the properties of light impinging on the retina. An experimental study was designed to quantify the effect of internal coloured surfaces on our circadian stimulation by daylight. Four identical models of a standard office were manufactured, equipped by wallpapers of different colours, and exposed to daylight. Illuminance and spectral distribution of light were measured at different positions along the room and the potential circadian stimulation was evaluated by an established model. The measurements have proven that although the visual comfort may be satisfactory, circadian stimulation may be inhibited, especially when room´s surfaces are yellow. Thus, proper choice of internal surfaces´ colours is important to prevent the potential negative health consequences.

Light-induced changes in the photosynthetic physiology and biochemistry in the diatom Skeletonema marinoi

Light is a driving force behind the synthesis of biomass in photoautotrophs. In pelagic ecosystems, highly variable light strongly affects microalgae at an ecological (success and succession), molecular (acclimation, carbon allocation), photosynthetic and growth levels. Therefore, manipulation of light appears to be an attractive tool for enhancing growth of microalgae in order to extend the use of these organisms in biotechnological field. In this study, we investigate the responses of the diatom alga Skeletenoma marinoi to different growth light regimes, that induced composite acclimative patterns manifesting in strong alterations in the cell biology. Although the growth rate is dependent upon the integrated daily light dose received by the algae, we demonstrate that physiological and biochemical acclimation responds to additional light stimuli. The application of fluctuating red light on a sinusoidal blue light spectral distribution induces an increase in non-photochemical quenching and the de-epoxidation state of the xanthophyll cycle along with modifications of the metabolic state of the cells, e.g. an increase in carbohydrates, glycolipids and saturated fatty acids. Providing an unnatural square-wave light course induces drastic changes in photosynthesis, pigment and macromolecular composition of the cells.

Light irradiance and spectral distribution effects on cyanobacterial hydrogen production

Light is an essential energy source for photosynthetic cyanobacteria. Changes in both light irradiance and spectral distribution will affect their photosynthetic productivity. Compared to the light irradiance, little investigations have been carried out on the effect of light spectra towards cyanobacterial hydrogen production. Hence, this work aims to investigate the effects of both light quantity and quality on biohydrogen productivity of heterocystous cyanobacterium, A.variabilis. Under white light condition, the highest hydrogen production rate of 31 µmol H2 mg chl a -1 h-1 was achieved at 70 µE m-2 s-1. When the experiment was repeated at the same light irradiance but different light spectra of blue, red and green, the accumulations of hydrogen were significantly lower than the white light except for blue light. As the light irradiance was increased to 350 µE m-2 s-1, the accumulated hydrogen under the blue light doubled that of the white light. Besides that, an unusual prolongation of the hydrogen production up to 120 h was observed. The results obtained suggest that blue light could be the most desirable light spectrum for cyanobacterial hydrogen production.