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The correlated color temperature (CCT) and color rendering index (CRI) are two significant indicators related to the color appearance and visual effects of illumination. This paper concentrates on dynamic dimming for phosphor-converted (PC) white LEDs to achieve tunable CCT and adequate CRI, via compensation of red/green spectra. The LED systems described have a simple configuration consisting of a PC white LED, a monochrome green LED and a monochrome red LED, which can be individually driven. Compared to individual PC white LEDs, both the spectral continuity and uniformity of the mixed white light are enhanced. The tunable dimming models are proposed by combination of spectral colorimetry and photo-electro-thermal (PET) theory, thus multi-physics effects are involved. From the modeling process and results, the nonlinear characteristics are observed. Experimental verifications present good agreement existing between calculations and measurements, both in terms of values and variation trends. These proposed models could be effective tools to figure out photometric characteristics and visual perception of illumination. On the other hand, they could provide schemes of reference to improve the illumination environment adapting to various special occasions and personal preferences.

The effect of active and passive power supply modes on the resistance of light-emitting diodes (LEDs) fabricated on the basis of a multilayer AlGaAs heterostructure to irradiation by gamma quanta has been studied. For the LEDs under study, regardless of the power regime during irradiation, three characteristic stages of radiation power reduction were distinguished; in this case, the second stage is characterized by a higher damage factor, and the third stage is characterized by the appearance of catastrophic failures. During irradiation of LED in the active power mode, two differently directed processes of change in the radiation power are observed. It is assumed that the first process is due to a decrease in the LED radiation power owing to the introduction of the corresponding radiation defects. The second process is due to the partial restoration of the radiation power owing to radiation, radiation-thermal, and/or electrically stimulated annealing of a part of the created defects. The observed restoration of the radiation power in the active power supply mode of the LED during irradiation significantly increases its resistance to irradiation with gamma quanta. [ABSTRACT FROM AUTHOR]

In this study, blue perovskite quantum dots (PQDs) were prepared using didodecyldimethylammonium bromide (DDAB), which can passivate surface defects caused by the loss of surface ligands and reduce particle size distribution. After the passivation of DDAB, blue CsPbClxBr3−x PQDs dispersed in n-octane produced a more compact and uniform PQD thin film than the non-passivated ones. The resulting device showed a stabile lifetime, and an EL peak of 470 nm and a maximum EQE of 1.63% were obtained at an operating voltage of 2.6 V and a current density of 0.34 mA/cm2. This work aims to provide a simple method to prepare blue-emitting PQDs and high-performance PQD-based light-emitting devices. [ABSTRACT FROM AUTHOR]

Light-emitting diodes (LED) are widely employed in display applications and lighting systems. Further research on LED that incorporates carbon nanostructures and metal nanoparticles exhibiting surface plasmon resonance has demonstrated a significant improvement in device performance. These devices offer lower turn-on voltages, higher external quantum efficiencies, and luminance. De facto, plasmonic nanoparticles, such as Au and Ag have boosted the luminance of red, green, and blue emissions. When combined with carbon nanostructures they additionally offer new possibilities towards lightweight and flexible devices with better thermal management. This review surveys the diverse possibilities to combine various inorganic, organic, and carbon nanostructures along with plasmonic nanoparticles. Such combinations would allow an enhancement in the overall properties of LED.

Keywords: passive optical networks (PON); visible-light communication (VLC); light-emitting diodes (LED); optical wireless communication (OWC); infrared LED (IR-LED) EN passive optical networks (PON) visible-light communication (VLC) light-emitting diodes (LED) optical wireless communication (OWC) infrared LED (IR-LED) 379 383 5 07/05/22 20220701 NES 220701 1 Introduction Nowadays, requirements for high-speed and high-capacity networks are increasing with a great pace, more often in buildings, due to the greater use of Internet services and online games [[1], [3]]. To provide solution to microwave frequency-dependent communication, optical wireless communication using visible-light communication (VLC) is recognized as the potential way out and premier alternative based on low-cost light-emitting diodes (LEDs) [[5]]. Passive optical networks (PON), visible-light communication (VLC), light-emitting diodes (LED), optical wireless communication (OWC), infrared LED (IR-LED) 5 Wang Y, Wang Y, Chi N, Yu J, Shang H. Demonstration of 575-Mb/s downlink and 225-Mb/s uplink bi-directional SCM-WDM visible light communication using RGB LED and phosphor-based LED. [Extracted from the article]

PurposeComputer vision syndrome (CVS) is one of the most frequently encountered problems among video display terminals (VDT) users, but little is known regarding the short-term effect after exposure to light-emitting diodes (LED). The purpose of this study was to determine if short-term exposure to LED leads to changes in corrected distance visual acuity (CDVA), lipid layer thickness (LLT), blink rates, partial blink ratio, and computer vision syndrome questionnaire (CVS-Q) score.DesignProspective, cross-sectional study.MethodsIn this study, participants were recruited at the National Cheng-Kung University Hospital, a tertiary referral center in southern Taiwan, for examination. Participants were asked to complete the CVS-Q and undergo a series of ocular examinations, including CDVA, LLT, blink rates and partial blink ratio before and after watching an LED display for 15 min. Main Outcome Measures were changes in CDVA, LLT, blink rates, partial blink ratio, and CVS-Q measurements.ResultsIn total, 120 eyes from 60 participants (mean age: 35.7 ± 9.4 years) were included; 31 participants were men (51.7%), and 29 were women (48.3%). The CDVA, LLT, blink rates, and partial blink ratio did not change after watching the LED display. The CVS-Q score significantly improved after short-term LED exposure (P < 0.001). A subgroup analysis of subjects with a baseline LLT of

This article presents a deep analysis of the low-frequency ripple transferred from the bus voltage to the light-emitting diode (LED) current in integrated two-stage power converters, operating as offline LED drivers. This analysis presents a design methodology to select the optimum power control stage converter to the LED load and to reduce the bulk capacitance. The main focus is to analyze the ripple transfer ratio of the three main nonisolated dc–dc converters, namely buck, boost, and buck–boost. Moreover, this article presents a step-by-step case study for an existing converter and the proposed converter supplying a 26.9-W Luxeon 3014 LED load. The experimental results show that the integrated buck and boost converter requires a bus capacitance of 1200 μF, whereas in the integrated buck and buck–boost converter, the capacitance is reduced to 680 μF by applying the method proposed. This represents that the replacement of a boost converter by a buck–boost converter on the second stage allows a 50% reduction of the bus capacitance while keeping the same current ripple. [ABSTRACT FROM AUTHOR]

The color, electrical, optical and thermal properties of light-emitting diode (LED) systems are highly dependent on one another. This paper proposes an analysis model that links the optical power, correlated color temperature (CCT), and circadian action factor (CAF) together with the electrical and thermal effects of phosphor-converted LEDs. The proposed model applies to tunable white LED systems with various color temperatures of LEDs whose spectral power distribution (SPD) can be individually controlled. The total optical power is due to the combined emitted optical power of both LEDs, the overall CCT is built upon a non-linear empirical LED model, and the overall CAF is quantified based on an extended Gaussian SPD model. The proposed prediction model consists a series of optical and chromatic evaluation, with which it is simple for LED system designers to comply. In model verification, the bi-color white LED source made up of a warm color LED (2700 K) and a cool color LED (7600 K) is adopted, with good agreement between the calculated and experimental results.

In this study, blue perovskite quantum dots (PQDs) were prepared using didodecyldimethylammonium bromide (DDAB), which can passivate surface defects caused by the loss of surface ligands and reduce particle size distribution. After the passivation of DDAB, blue CsPbClxBr3−x PQDs dispersed in n-octane produced a more compact and uniform PQD thin film than the non-passivated ones. The resulting device showed a stabile lifetime, and an EL peak of 470 nm and a maximum EQE of 1.63% were obtained at an operating voltage of 2.6 V and a current density of 0.34 mA/cm2. This work aims to provide a simple method to prepare blue-emitting PQDs and high-performance PQD-based light-emitting devices.

We investigated the influence of different conditions (light composition and plant growth regulators (PGRs) in culture media) on the morphophysiological parameters of Stevia rebaudiana Bertoni in vitro and in vivo. Both PGRs and the light spectra applied were found to significantly affect plant morphogenesis. During the micropropagation stage of S. rebaudiana, optimal growth, with a multiplication coefficient of 15, was obtained in an MS culture medium containing 2,4-epibrassinolide (Epin) and indole-3-acetic acid (IAA) at concentrations of 0.1 and 0.5 mg L-1, respectively. During the rooting stage, we found that the addition of 0.5 mg L-1 hydroxycinnamic acid (Zircon) to the MS medium led to an optimal root formation frequency of 85% and resulted in the formation of strong plants with well-developed leaf blades. Cultivation on media containing 0.1 mg L-1 Epin and 0.5 mg L-1 IAA and receiving coherent light irradiation on a weekly basis resulted in a 100% increase in the multiplication coefficient, better adventitious shoot growth, and a 33% increase in the number of leaves. S. rebaudiana microshoots, cultured on MS media containing 1.0 mg L-1 6-benzylaminopurine (BAP) and 0.5 mg L-1 IAA with red monochrome light treatments, increased the multiplication coefficient by 30% compared with controls (white light, media without PGRs). [ABSTRACT FROM AUTHOR]

Consideration is given to the possibility of using LED light sources with different ratios of red (650 - 660 nm), orange (600 - 610 nm) and blue (440 - 450 nm) light in the light flux in the rooting stage of garden strawberry (Fragaria × ananassa (Duch. ex Weston) Duch. ex Rozier) grown in vitro. The study covered a sizable diversity of strawberry cultivars (selected from the in vitro collection): ‘Borovitskaya’, ‘Vityaz’, ‘Zenga Zengana’, ‘Khoney’, ‘Tsaritsa’, ‘Kubata’, ‘Dukat’, ‘Marmalada’, ‘Valenta’, ‘Rusich’, ‘Krasavitsa Zagorya’, ‘Neznakomka’ and ‘Roksana’, thus ensuring quite diversified results. It was established that the use of LED sources with an increased content of red light in the light flux increased the rooting percentage (1.15-1.25 times) and the number of roots per one microcutting (1.29-1.77 times) in in vitro culture, as compared with fluorescent lamp lighting. It was observed that with different spectral compositions of light the rooting ability of microcuttings was cultivar-specific.

In this paper, a 3D indoor visible light positioning (VLP) system with fast computation time using received signal strength (RSS) is proposed and experimentally demonstrated. Assisted by the deep learning techniques, the complexity of the trilateration problem is greatly reduced, and the trilateration problem can be formulated as a linear mapping leading to faster position estimation than the conventional estimation. Moreover, a new method of off-line preparation is adopted to minimize the workload of the VLP system deployment for more practical usage. The proposition is implemented on an atto-cellular VLP unit, through which the real-time performance and positioning accuracy are demonstrated and validated in a 3D positioning experiment performed in a space of 1.2 × 1.2 × 2 m3. The experimental results show that a positioning accuracy of 11.93 cm in confidence of 90% is achieved with 50 times faster the computation time compared to the conventional scheme.

The color, electrical, optical and thermal properties of light-emitting diode (LED) systems are highly dependent on one another. This paper proposes an analysis model that links the optical power, correlated color temperature (CCT), and circadian action factor (CAF) together with the electrical and thermal effects of phosphor-converted LEDs. The proposed model applies to tunable white LED systems with various color temperatures of LEDs whose spectral power distribution (SPD) can be individually controlled. The total optical power is due to the combined emitted optical power of both LEDs, the overall CCT is built upon a non-linear empirical LED model, and the overall CAF is quantified based on an extended Gaussian SPD model. The proposed prediction model consists a series of optical and chromatic evaluation, with which it is simple for LED system designers to comply. In model verification, the bi-color white LED source made up of a warm color LED (2700 K) and a cool color LED (7600 K) is adopted, with good agreement between the calculated and experimental results. [ABSTRACT FROM AUTHOR]

Red plus blue light-emitting diodes (LEDs) are commonly applied in plant factories with artificial lighting due to photosynthetic pigments, which absorb strongly in red and blue light regions of the spectrum. However, plants grown under natural environment are used to utilizing broad-wide spectrum by long-term evolution. In order to examine the effects of addition light added in red plus blue LEDs or white LEDs, green and purple leaf lettuces (Lactuca sativa L. cv. Lvdie and Ziya) were hydroponically cultivated for 20 days under white LEDs, white plus red LEDs, red plus blue LEDs, and red plus blue LEDs supplemented with ultraviolet, green or far-red light, respectively. The results indicated that the addition of far-red light in red plus blue LEDs increased leaf fresh and dry weights of green leaf lettuce by 28% and 34%, respectively. Addition of ultraviolet light did not induce any differences in growth and energy use efficiency in both lettuce cultivars, while supplementing green light with red plus blue LEDs reduced the vitamin C content of green leaf lettuce by 44% and anthocyanin content of purple leaf lettuce by 30% compared with red plus blue LEDs, respectively. Spectral absorbencies of purple leaf lettuce grown under red plus blue LEDs supplemented with green light were lower in green light region compared with those grown under red plus blue LEDs, which was associated with anthocyanin contents. White plus red LEDs significantly increased leaf fresh and dry weights of purple leaf lettuce by 25%, and no significant differences were observed in vitamin C and nitrate contents compared with white LEDs. Fresh weight, light and electrical energy use efficiencies of hydroponic green and purple leaf lettuces grown under white plus red LEDs were higher or no significant differences compared with those grown under red plus blue LEDs. In conclusion, white plus red LEDs were suggested to substitute for red plus blue LEDs in hydroponic lettuce (cv. Lvdie and Ziya) production in plant factories with artificial lighting. [ABSTRACT FROM AUTHOR]

Three novel poly(2,7‐carbazole)s having hole injection and transporting pendent moieties of carbazole and triphenylamine at the N‐position were synthesized for achieving pure blue electroluminescence. The N‐pendants in the polymers correspond to N‐phenylcarbazol‐2‐yl (P1), N,N‐diphenylamino‐N‐phenylcarabazol‐2‐yl (P2), and 4‐phenyl having a hydrocarbon chain with a triphenylamine terminal (P3), respectively. Electronic, optical, and electroluminescence properties of these polymers were compared with those of a poly(2,7‐carbazole) directly connected with triphenylamine at the N‐position (P0) having an aggregation‐induced emissive property. The photoluminescence (PL) spectra suggested that they could emit in the region of blue light in the film state. Especially, P2 that has the fixed and large diphenylaminocarbazolyl pendant showed a deep‐blue fluorescence with CIE(x, y) = (0.15, 0.07). The P0, P2, and P3 based light emitting diode devices showed maximum electroluminescence wavelengths in the range of 430–450 nm. The P2 device showed pure blue emission (CIE[x, y] = [0.18, 0.16]), high luminance (1130 cd/m2) and current density (628 mA/cm2) at 8 V, whereas low‐energy emissions around 500–600 nm were emerged at higher than 9 V. The P0 and P3 devices also showed a blue electroluminescence in the range of 8–11 V, but their luminance and efficiency were low. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 2526–2534 [ABSTRACT FROM AUTHOR]

We investigated the influence of different conditions (light composition and plant growth regulators (PGRs) in culture media) on the morphophysiological parameters of Stevia rebaudiana Bertoni in vitro and in vivo. Both PGRs and the light spectra applied were found to significantly affect plant morphogenesis. During the micropropagation stage of S. rebaudiana, optimal growth, with a multiplication coefficient of 15, was obtained in an MS culture medium containing 2,4-epibrassinolide (Epin) and indole-3-acetic acid (IAA) at concentrations of 0.1 and 0.5 mg L−1, respectively. During the rooting stage, we found that the addition of 0.5 mg L−1 hydroxycinnamic acid (Zircon) to the MS medium led to an optimal root formation frequency of 85% and resulted in the formation of strong plants with well-developed leaf blades. Cultivation on media containing 0.1 mg L−1 Epin and 0.5 mg L−1 IAA and receiving coherent light irradiation on a weekly basis resulted in a 100% increase in the multiplication coefficient, better adventitious shoot growth, and a 33% increase in the number of leaves. S. rebaudiana microshoots, cultured on MS media containing 1.0 mg L−1 6-benzylaminopurine (BAP) and 0.5 mg L−1 IAA with red monochrome light treatments, increased the multiplication coefficient by 30% compared with controls (white light, media without PGRs).

Free‐radical photopolymerization is scarcely used for the manufacturing of fiber‐reinforced polymers. The main issue relies on the penetration depth of light which affects the conversion degree when photopolymerizing thick samples. Consequently, this could lead to inhomogeneous polymer properties. The ability of acylphosphine oxides to photobleach under near UV irradiation makes them of great interest for the curing of thick samples. Therefore, the influence of (2,4,6‐trimethylbenzoyl) phosphine oxide on the curing of composites under LED is investigated. Although that a frontal photopolymerization process can be evidenced, it was found that full photobleaching is hardly obtained at high concentration of photoinitiator. Six layers laminates made of unidirectional fiber glass and unsaturated polyester resin were prepared. The existence of an optimal range of concentration for which the conversion of the resin is the most homogeneous throughout its thickness was pointed out, a fact that is confirmed by dynamic mechanical analysis. Interestingly, this effect is reflected in the shrinkage of the resin as shown by direct measurements or deflection experiments. Mechanical analysis was undertaken whose results correlate well with the aforementioned study, demonstrating the occurrence of a balance between the concentration of photoinitiator and the mechanical properties of the samples. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 898–906 The effect of the penetration depth of light during the frontal free‐radical photopolymerization of LED‐cured fiber‐reinforced polymers is studied. The photobleaching of the photoinitator is shown to be incomplete, leading to inhomogeneities in properties. An optimal range of photoinitiator concentration is pointed out which allows the formation of high performance composites. [ABSTRACT FROM AUTHOR]

Abstract A high power light-emitting diodes (LED) light source, which is assembled by many LED chips and heat sink, has a not uniform temperature distribution at working condition. Analysis and prediction of a high-power LED system lifetime are complicated and time-consuming. In this study, two artificial neural networks (ANN) are employed to simplify the LED lighting system's lifetime prediction and increase the precision of such analysis. The temperature distribution of the high power light source is calculated by Finite element method (FEM) with LED chip photo-electro-thermal (PET) ANN. With the precise LED temperature distribution, the lifetime for multi-chip high-power LED light source can be predicted by lifetime ANN. The PET ANN is used to simplify the multi-physics coupling in LED PET analyzing. The lifetime ANN can predict the lifetime of a LED chip across a wide range of temperatures and not merely corresponding to several testing and interpolation points. This work aims to rapidly analyze multi-chip high-power lighting systems characteristics. The repeated tests and calculations of PET and lifetime are avoided with this method. This approach presents a new and effective way to assess the reliability of high-power LED light source. [ABSTRACT FROM AUTHOR]

Vascular diseases are becoming an epidemic with an increasing aging population and increases in obesity and type II diabetes. Point-of-care (POC) diagnosis and monitoring of vascular diseases is an unmet medical need. Photoacoustic imaging (PAI) provides label-free multiparametric information of deep vasculature based on strong absorption of light photons by hemoglobin molecules. However, conventional PAI systems use bulky nanosecond lasers which hinders POC applications. Recently, light-emitting diodes (LEDs) have emerged as cost-effective and portable optical sources for the PAI of living subjects. However, state-of-art LED arrays carry significantly lower optical energy (

The possibility of prolonging space missions—and consequently the permanence of humans in space—depends on the possibility of providing them with an adequate supply of fresh foods to meet their nutritional requirements. This would allow space travelers to mitigate health risks associated with exposure to space radiation, microgravity and psychological stress. In this review, we attempt to critically summarize existing studies with the aim of suggesting possible solutions to overcome the challenges to develop a bio-regenerative life support system (BLSS) that can contribute to life support, supplying food and O2, while removing CO2 on the International Space Station (ISS). We describe the physical constraints and energy requirements for ISS farming in relation to space and energy resources, the problems related to lighting systems and criteria for selecting plants suitable for farming in space and microgravity. Clearly, the dimensions of a growth hardware that can be placed on ISS do not allow to produce enough fresh food to supplement the stored, packaged diet of astronauts; however, experimentation on ISS is pivotal for implementing plant growth systems and paves the way for the next long-duration space missions, including those in cis-lunar space and to the lunar surface.

Photoacoustic computed tomography (PACT) has been widely explored for non-ionizing functional and molecular imaging of humans and small animals. In order for light to penetrate deep inside tissue, a bulky and high-cost tunable laser is typically used. Light-emitting diodes (LEDs) have recently emerged as cost-effective and portable alternative illumination sources for photoacoustic imaging. In this study, we have developed a portable, low-cost, five-dimensional (x, y, z, t, λ ) PACT system using multi-wavelength LED excitation to enable similar functional and molecular imaging capabilities as standard tunable lasers. Four LED arrays and a linear ultrasound transducer detector array are housed in a hollow cylindrical geometry that rotates 360 degrees to allow multiple projections through the subject of interest placed inside the cylinder. The structural, functional, and molecular imaging capabilities of the LED−PACT system are validated using various tissue-mimicking phantom studies. The axial, lateral, and elevational resolutions of the system at 2.3 cm depth are estimated as 0.12 mm, 0.3 mm, and 2.1 mm, respectively. Spectrally unmixed photoacoustic contrasts from tubes filled with oxy- and deoxy-hemoglobin, indocyanine green, methylene blue, and melanin molecules demonstrate the multispectral molecular imaging capabilities of the system. Human-finger-mimicking phantoms made of a bone and blood tubes show structural and functional oxygen saturation imaging capabilities. Together, these results demonstrate the potential of the proposed LED-based, low-cost, portable PACT system for pre-clinical and clinical applications.

The effect of light-emitting diodes (LEDs) on the production of secondary metabolites in medicinal plants and hairy roots is receiving much attention. The roots and rhizomes of the traditional Chinese medicinal plant Salvia miltiorrhiza Bunge are widely used for treating cardiovascular and cerebrovascular diseases. The main components are liposoluble tanshinones and hydrophilic phenolic acids. Moreover, hairy root culture of S. miltiorrhiza has been used in research of valuable plant-derived secondary metabolites. In this study, we examined the effect of LEDs with different combinations of wavelengths on the content of the main components in hairy roots of S. miltiorrhiza . Tanshinone IIA (TSIIA) content in hairy roots was significantly decreased with all light treatments containing blue light by >60% and was 9 times lower with LED treatment duration changed from 1 week to 3 weeks. HMGR , DXS2 , DXR , GGPPS , CPS and CYP76AH1 genes involved in the tanshinone biosynthesis pathway were downregulated by blue light. Furthermore, light quality treatments have different effect on the accumulation of phenolic acids in hairy roots of S. miltiorrhiza . The light treatments 6R3B, 6B3IR, 7RGB and 2R6BUV for 3 weeks could increase rosmarinic acid (RA) content slightly but not salvianolic acid B (SAB) content. Different secondary metabolite contents could be regulated by different wavelength combinations of LEDs. Blue light could reduce TSIIA content in hairy roots of S. miltiorrhiza via gene regulation. [ABSTRACT FROM AUTHOR]

We present a freeform lens for application to light-emitting diodes (LED) road lighting. We propose a simple source-target luminous intensity mapping method based on Snell's law and geometric-optics analysis. We calculated different contours of cross-sections to construct a freeform lens with a smooth surface. The computer simulation results show that the lighting performance of a single freeform lens is not sufficient for road lighting. For the road lamp simulation, we adopted an oval arrangement of freeform lenses on a printed circuit board. In addition, we performed tolerance analysis to determine the tolerance limits of manufacturing and installation errors. A road lamp at a height of 12 m can create rectangular illumination with an area of 40 m × 12 m, 69.7% uniformity, and average illuminance of 24.6 lux. This lighting performance can fully comply with the urban road lighting design standard. [ABSTRACT FROM AUTHOR]

Advancements in light-emitting diode (LED) technology have made them a viable alternative to current lighting systems for both sole and supplemental lighting requirements. Understanding how wavelength specific LED lighting can affect plants is thus an area of great interest. Much research is available on the wavelength specific responses of leaves from multiple crops when exposed to long-term wavelength specific lighting. However, leaf measurements do not always extrapolate linearly to the complexities which are found within a whole plant canopy, namely mutual shading and leaves of different ages. Taken together, both tomato (Solanum lycopersicum) leaves under short-term illumination and lisianthus (Eustoma grandiflorum) and tomato whole plant diurnal patterns of plants acclimated to specific lighting indicate wavelength specific responses of both H2O and CO2 gas exchanges involved in the major growth parameters of a plant. Tomato leaves grown under a white light source indicated an increase in transpiration rate and internal CO2 concentration and a subsequent decrease in water-use-efficiency (WUE) when exposed to a blue LED light source compared to a green LED light source. Interestingly, the maximum photosynthetic rate was observed to be similar. Using plants grown under wavelength specific supplemental lighting in a greenhouse, a decrease in whole plant WUE was seen in both crops under both red-blue (RB) and red-white (RW) LEDs when compared to a high pressure sodium (HPS) light. Whole plant WUE was decreased by 31% under the RB LED treatment for both crops compared to the HPS treatment. Tomato whole plant WUE was decreased by 25% and lisianthus whole plant WUE was decreased by 15% when compared to the HPS treatment when grown under RW LED. The understanding of the effects of wavelength specific lighting on both leaf and whole plant gas exchange has significant implications on basic academic research as well as commercial greenhouse production.

By modifying traditional remote phosphor-diffuser-packaged light-emitting diode systems, we have managed to increase the luminous efficacy from 145.7 to 162.3 lm/W. One mechanism responsible for this achievement is associated with randomizing the directions of light beams transmitting through an interior diffuser, whose position is optimized based on an overall merit. The other mechanism is identified as the gradual attenuation of the undesirable blue-ring image along the distance from the diffuser toward the phosphor base. The identification of these two mechanisms is verified by luminous efficacy measurements, 3-D image plots, and combined Monte Carlo algorithm ray tracing simulation results. In addition, merits related to correlated color temperatures and issues pertaining to costs are briefly discussed.

Liquid crystal displays (LCDs) are used as screens in consumer electronics and are indispensable in the modern era of computing. LCDs utilize light-emitting diodes (LEDs) as backlight modules and emit high levels of blue light, which may cause retinal photoreceptor cell damage. However, traditional blue light filters may decrease the luminance of light and reduce visual quality. We adjusted the emitted light spectrum of LED backlight modules in LCDs and reduced the energy emission but maintained the luminance. The 661W photoreceptor cell line was used as the model system. We established a formula of the ocular energy exposure index (OEEI), which could be used as the indicator of LCD energy emission. Cell viability decreased and apoptosis increased significantly after exposure to LCDs with higher emitted energy. Cell damage occurred through the induction of oxidative stress and mitochondrial dysfunction. The molecular mechanisms included activation of the NF-κB pathway and upregulation of the expression of proteins associated with inflammation and apoptosis. The effect was correlated with OEEI intensity. We demonstrated that LCD exposure-induced photoreceptor damage was correlated with LCD energy emission. LCDs with lower energy emission may, therefore, serve as suitable screens to prevent light-induced retinal damage and protect consumers’ eye health.

Dengue fever is the most serious vector-borne disease in Asia. There are still no dengue vaccines or therapeutic drugs, and vector-mosquito control is the main prevention and treatment method. The prevention and control of dengue-fever vector mosquitoes in Taiwan is still dominated by larval control. However, the removal of the source of mosquito-borne diseases has not been fully implemented, and the removal process of vector-borne mosquitoes cannot keep up with their breeding rate. In addition, chemical agents used in the elimination of pathogenic mosquitoes may cause mosquito resistance and environmental pollution. Therefore, it is important to develop new prevention and control technologies. This study is dedicated to the development of a mosquito trapping optical system with high efficiency and low glare that is safe for humans. The system is mainly equipped with ultraviolet light-emitting diodes (UV-LED), a freeform-surfaced optical reflector, and a photocatalyst. The reflector can lead light downward for the protection of user eyes, and expand the range of trapping mosquitoes to 225 π m2. Based on practical experiments, captured mosquitoes increased by about 450% through the proposed system compared to conventional traps using UV LED. In addition, the proposed system is shown to be 45% more enhanced in trapping capability after a photocatalyst (titanium dioxide) coating is applied to its reflector.

Purpose: The zebrafish is an established animal model commonly used in biological, neuroscience, and genetic research. We have developed a new light stimulating system using white light-emitting diodes (LEDs) to elicit ERGs from zebrafish larvae. The purpose of this study was to record full-field ERGs and to evaluate the inter-trial reliability of the ERGs recorded with our system from zebrafish larvae. Methods: The stimulating device used white LEDs that were attached to a stereomicroscope, and the location of the recording electrode on the cornea could be monitored while the eye was being stimulated. Full-field scotopic and photopic ERGs were recorded from larvae at the age of 5-7 days post-fertilization (dpf). Intensity-response curves were constructed from the ERGs. Inter-trial reliability of the ERGs recorded by our system was evaluated. Results: This stimulating system could be used for efficient and reliable ERG recordings from 5-7 dpf larvae. The amplitudes, implicit times, and the waveforms of the scotopic and photopic ERGs were similar to those reported in earlier studies. Inter-trial reliability of the amplitudes of the photopic ERG b-waves was excellent with an intra-class correlation coefficient of 0.98. Conclusion: We conclude that this new light stimulation system using white LEDs attached to a stereomicroscope will be helpful in recording reliable ERGs from zebrafish larvae. [ABSTRACT FROM AUTHOR]

To alleviate the mismatch between electron/hole velocities and improve the quantum efficiencies, the cobalt-doped ZnO (CZO) dilute magnetic films grown by pulsed-laser deposition at a low temperature of 100 °C were served as the external electron retarding n-electrodes for vertical InGaN light-emitting diodes (LEDs). The retardation of the electron mobility is owing to the scatter of electrons via the spin-orbit interaction of Co2+ ions and their corresponding ferromagnetic properties. A 150-nm-thick CZO film was chosen as the n-electrode for the vertical green LED (530 nm). In comparison to conventional lateral LED, the vertical LEDs without and with the CZO n-electrode had 21.3% and 39.6% improvements in the output power (at 350 mA), respectively. The vertical LED with the CZO n-electrode showed an increment in the light output power (at 350 mA) by 15.1% as compared with the vertical LED without the CZO n-electrode. Obviously, after inserting the CZO n-electrode, the excessively large mobility difference between the electron and hole carriers in the conventional vertical LED is reduced significantly, which can decrease the nonradiative recombination rate and improve the emission characteristic. The results also reveal the CZO film served as an external electron retarding electrode is highly potential for vertical LED applications. [ABSTRACT FROM PUBLISHER]

ABSTRACT Two new electron-transporting copolyphenylenes P1NH and P2NH possessing balanced charges crucial to emission efficiency of polymer light-emitting diodes (PLEDs) have been synthesized and applied as an electron-transporting layer (ETL). The main chain structure is all para-linkage for P1NH and both para- and meta-linkage for P2NH, with the same pendant electron-withdrawing benzimidazolyl and polar diethanolaminohexyloxy groups. Both copolymers possess excellent thermal stability ( Td > 300 °C, Tg > 100 °C) due to their rigid backbones. In addition, the pendant groups effectively lower LUMO (∼ −2.70 eV) and HOMO (∼ −5.70 eV) levels, resulting in improved electron-transporting and hole-blocking capabilities. Multilayer yellow-emitting PLEDs with a configuration of ITO/PEDOT:PSS/SY/ETL/LiF/Al were successfully fabricated by the spin-coating process. The maximum luminance and maximum current efficiency of the P1NH-based device were 12,881 cd/m2 and 10.94 cd/A, respectively, superior to the performance of P2NH-based device (4938 cd/m2, 3.70 cd/A) and the device without ETL (8690 cd/m2, 2.78 cd/A). Current results indicate that P1NH is highly effective in enhancing electron transport and device performance. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 2494-2505 [ABSTRACT FROM AUTHOR]

ABSTRACT Blue light-emitting polyfluorenes, PPF-FSOs and PPF-SOFs were synthesized via introducing spiro[fluorene-9,9′-thioxanthene- S,S-dioxide] isomers (2,7-diyl and 2′,7′-diyl) (FSO/SOF) into the poly[9,9-bis(4-(2-ethylhexyloxy) phenyl)fluorene-2,7-diyl] (PPF) backbone, respectively. With the increasing contents of FSO and SOF moieties, the absorption and PL spectra of PPF-FSOs show slight red shift, while that of PPF-SOFs exhibit blue shift, respectively. The HOMO and LUMO levels reduce gradually with increasing SOF unit in PPF-SOFs. The polymers emit blue light peaked around 430-445 nm and show an excellent spectral stability with the variation in current densities. The distinctly narrowing EL spectra were observed with the incorporation of isomers in the polymers. The full width at half maximum reduced by 15 nm for PPF-SOFs, resulting in a blue shift with the CIE coordinates from (0.16, 0.11) to (0.16, 0.08). With a device configuration of ITO/PEDOT:PSS/EML/CsF/Al, a maximum luminance efficiency (LEmax) of 2.00 cd A−1, a maximum external quantum efficiency (EQEmax) of 3.76% with the CIE coordinates of (0.16, 0.08) for PPF-SOF15 and a LEmax of 1.68 cd A−1, a EQEmax of 2.38% with CIE (0.16, 0.12) for PPF-FSO10 were obtained, respectively. The result reveals that spiro[fluorene-9,9′-thioxanthene- S,S-dioxide] isomers are promising blocks for deep-blue light-emitting polymers. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 2332-2341 [ABSTRACT FROM AUTHOR]

Advancements in light-emitting diode (LED) technology have made them a viable alternative to current lighting systems for both sole and supplemental lighting requirements. Understanding how wavelength specific LED lighting can affect plants is thus an area of great interest. Much research is available on the wavelength specific responses of leaves from multiple crops when exposed to long-term wavelength specific lighting. However, leaf measurements do not always extrapolate linearly to the complexities which are found within a whole plant canopy, namely mutual shading and leaves of different ages. Taken together, both tomato (Solanum lycopersicum) leaves under short-term illumination and lisianthus (Eustoma grandiflorum) and tomato whole plant diurnal patterns of plants acclimated to specific lighting indicate wavelength specific responses of both H2O and CO2 gas exchanges involved in themajor growth parameters of a plant. Tomato leaves grown under a white light source indicated an increase in transpiration rate and internal CO2 concentration and a subsequent decrease in water-use-efficiency (WUE) when exposed to a blue LED light source compared to a green LED light source. Interestingly, the maximum photosynthetic rate was observed to be similar. Using plants grown under wavelength specific supplemental lighting in a greenhouse, a decrease in whole plant WUE was seen in both crops under both red-blue (RB) and red-white (RW) LEDs when compared to a high pressure sodium (HPS) light. Whole plant WUE was decreased by 31% under the RB LED treatment for both crops compared to the HPS treatment. Tomato whole plant WUE was decreased by 25% and lisianthus whole plant WUE was decreased by 15% when compared to the HPS treatment when grown under RW LED. The understanding of the effects of wavelength specific lighting on both leaf and whole plant gas exchange has significant implications on basic academic research as well as commercial greenhouse production. [ABSTRACT FROM AUTHOR]

Relative reflected intensity of the incident exciting light is proposed to measure the junction temperature of light-emitting diodes (LEDs) under test. Reflectance spectra at a wide junction temperature range are acquired. Multichannel optical fibers greatly increase the collecting efficiency of the reflected light. Lock-in technique is utilized to exclude the interference of the emitting light from LEDs under test and to increase the dynamic range greatly. The results are in good agreement with those directly tested by a microthermocouple. To avoid extra carrier absorption and modulation effect, the incident exciting light should harbor smaller bandgap than that of LEDs under test. [ABSTRACT FROM AUTHOR]

Inevitable self-heating effects have been investigated for LEDs to date. In this paper, we present the thermally-induced penalty (TIP), and derive an upper external quantum efficiency (EQE) limit for a given bare LED by adding TIP to the real EQE. We find that the red-AlGaInP LED exhibits no efficiency droop under room temperature and the TIP is responsible for its real EQE droop. Among the TIPs of red, green, and blue LEDs, the red-AlGaInP LED suffers the most severe penalty. This TIP can serve as a criterion for LED cooling design, with its lower values leading to higher cooling rates. [ABSTRACT FROM AUTHOR]

Electronic waste (e-waste) is the world's fastest-growing type of waste, with lighting accounting for 9% of the total. Light-emitting diodes (LEDs) are composed of the most concentrated critical elements (Ag and Au) and recovery of these metals could generate economic benefits and reduce the burdens of environmental pollution; nevertheless, the absence of information about their composition currently presents a challenge in recycling these metals with minimal prospects for recovery. This study assessed the distribution and variation of elemental concentrations of 16 different elements in three generations of LEDs (12 different LED units): sub-mounted-device (SMD #10), chip-on-board (COB #1), and positive-intrinsic-negative (PIN #1). The SMD LEDs contained a considerable amount of Au with a median average concentration of 1204 mg/kg (ranging from 323 − 3687 mg/kg), which was similar to that of COB (1550 mg/kg), but higher than that of PIN LED (175 mg/kg). Based on the total threshold limiting concentration (TTLC), the Cu levels (605,823 mg/kg) in the SMD package exceeded the regulatory limits (2500 mg/kg). Concentrations of the hazardous elements Cr (29 mg/kg), Pb (12 mg/kg), Cd (0.1 mg/kg), and As (1 mg/kg) in the LED packages were within the regulatory limits. To recycle precious metals and other technological metals, a well-organized and dedicated optimized assessment of the value of metals is required especially in accordance with the concept of criticality and recyclability. Two factors, i.e., a high resource index (RI) and technology index (TI), suggest the importance of waste to the economy and has a significant potential for recycling with less processing burdens. Present findings indicated that the COB and a few of the studied SMD LEDs (3020, 4014, 5630, and 7020), exhibit high criticality and recyclability. For the RI and TI index, the contribution of metals such as Cu, Fe, Al, and Au were dominant. These findings can serve as a reference for the development of a viable approach for the recycling and recovery of targeted metals from LED e-waste. • The study assessed the concentrations of various metals in three generations of LEDs. • High amount of Au was found in SMD LEDs (1204 mg/kg) and COB LED (1550 mg/kg). • The Cu in SMD LEDs (605,823 mg/kg) exceeded the regulatory limit. • Hazardous elements (Cr, Pb, As, Cd) in LEDs were below the regulatory limit. • COB and a few SMD LEDs exhibit high criticality and recyclability. [ABSTRACT FROM AUTHOR]

In this paper, we demonstrate how driving current affects photometric performances of a white light organic light emitting diode (OLED) for general lighting purpose. Experiments reveal that a ripple current with 40% amplitude, 50-Hz–100-kHz frequency, and sinusoidal and triangle waveform has little influence on the test OLED. In the pulse-width modulation mode, both duty cycle and frequency of pulse current affect OLED's performance, and more particularly, their efficacy and correlated color temperature. Such influences become worse at high frequency and low duty cycle. The reason for this influence is a considerable difference between electron and hole mobility, and a time-dependent distribution of charge carrier within the structure leading to a movement of recombination zone therefrom. [ABSTRACT FROM AUTHOR]

The nonstoichiometric ITO/n-SiC/i-SiC/p-Si/Al light-emitting diodes (LEDs) with dense Si quantum dots (Si-QDs) embedded in the Si-rich SixC1-x -based i-SiC layer are demonstrated. The Si-rich SixC1-x films with buried Si-QDs are grown by the plasma-enhanced chemical vapor deposition with varying substrate temperatures. After the annealing process, the average Si-QD size in the Si-rich Si0.52C0.48 film is 2.7 ± 0.4 nm with a corresponding volume density of 1.43 × 1018 cm-3. By increasing the deposition temperatures from 300°C to 650°C, the turn-on voltage and turn-on current of the ITO/n-SiC/i-SiC/p-Si/Al LEDs are found to decrease from 13 to 4.2 V and from 0.63 to 0.34 mA, respectively. In addition, these Si-rich SixC1-x LEDs provide the maximal electroluminescent (EL) power intensity increasing from 1.1 to 4.5 μW/cm2. The yellow (at 570 nm) EL emission power of the ITO/n-SiC/i-SiC/p-Si/Al LEDs reveals a saturated phenomenon due to the Auger effect. The dissipated energy by the lattice thermal vibration contributes to a decayed EL emission power at higher biased currents. The corresponding power-current slope is observed to enhance from 0.45 to 0.61 μW/A with the substrate temperature increasing to 650°C.

Airports play a critical role in the air transport value chain. Each air transport value chain stakeholder requires energy to conduct their operations. Airports are extremely energy intensive. Greenhouse gases are a by-product from energy generation and usage. Consequently, airports are increasingly trying to sustainably manage their energy requirements as part of their environmental policies and strategies. This study used an exploratory qualitative and quantitative case study research approach to empirically examine Copenhagen Airport, Scandinavia’s major air traffic hub, sustainable airport energy management practices and energy-saving initiatives. For Copenhagen Airport, the most significant environmental impact factors occurring from energy usage are the CO2 emissions arising from both the air side and land side operations. Considering this, the airport has identified many ways to manage and mitigate the environmental impact from energy consumption on both the air and land side operations. Importantly, the application of technological solutions, systems and process enhancements and collaboration with key stakeholders has contributed to the airport’s success in mitigating the environmental impact from energy usage at the airport whilst at the same time achieving energy savings.

Results of using powerful LED matrices to inspect metal articles for hidden corrosion by active thermal-wave method are described. The effect of the color of paint-and-lacquer coating on the efficiency of heating with LED and halogen emitters is analyzed. The possibility of using powerful LED panels as thermal stimulation sources in portable flaw detectors is described. [ABSTRACT FROM AUTHOR]

ABSTRACT Six new conjugated polymers comprising of carbazole, fluorene, and ethylene dioxythiophene (EDOT) moieties along the backbone with a pendant cyano group attached to the ethylene moiety have been designed and synthesized via Sonogashira coupling polymerization reaction. Optical and electrochemical characterizations have shown that the energy band gaps lie within the range of 2.35-2.44 eV. Additionally, the presence of carbazole and EDOT makes these polymers better hole transporting materials, which is reflected from their low oxidation potential peaks (0.55-1.11 V) in cyclic voltammograms. Furthermore, the aggregation enhanced emission (AEE) phenomenon resulted in a 2.6-fold increase in fluorescence intensity in a 90:10 THF/water mixture in comparison to pristine THF. The AEE properties were further verified by DLS (dynamic light scattering) experiment and SEM (scanning electron microscopy) studies. Polymers in solution as well as in polystyrene matrix emit in the green region (quantum yield in solution state Φ f =41-43%) with CIE values (0.25-0.36, 0.52-0.57). Excellent thermal stability is observed for the new polymers. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 2774-2784 [ABSTRACT FROM AUTHOR]

ABSTRACT Two D-π-A-type 2,2,2-trifluoroacetophenone derivatives, namely, 4′-(4-( N, N-diphenyl)amino-phenyl)-phenyl-2,2,2-trifluoroacetophenone (PI-Ben) and 4′-(4-(7-( N, N-diphenylamino)-9,9-dimethyl- 9H-fluoren-2-yl)-phenyl-2,2,2-trifluoroacetophenone (PI-Flu), are developed as high-performance photoinitiators combined with an amine or an iodonium salt for both the free-radical polymerization of acrylates and the cationic polymerization of epoxides and vinyl ether upon exposure to near-UV and visible light-emitting diodes (LEDs; e.g., 365, 385, 405, and 450 nm). The photochemical mechanisms are investigated by UV-Vis spectra, molecular-orbital calculations, fluorescence, cyclic voltammetry, photolysis, and electron-spin-resonance spin-trapping techniques. Compared with 2,2,2-trifluoroacetophenone, both photoinitiators exhibit larger redshift of the absorption spectra and higher molar-extinction coefficients. PI-Ben and PI-Flu themselves can produce free radicals to initiate the polymerization of acrylate without any added hydrogen donor. These novel D-π-A type trifluoroacetophenone-based photoinitiating systems exhibit good efficiencies (acrylate conversion = 48%-66%; epoxide conversion = 85%-95%; LEDs at 365-450 nm exposure) even in low-concentration initiators (0.5%, w/w) and very low curing light intensities (1-2 mW cm−2). © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 1945-1954 [ABSTRACT FROM AUTHOR]