Low-power Light-emitting Diodes Research Articles

Achieving Multiwavelength Optical Amplification Based on Polymer Waveguides Doped with NaYF4:Er3+, Yb3+ Nanoparticles under Commercial and Convenient Led Pumping

AbstractRelying on a reverse energy transfer mechanism between erbium (Er3+) and ytterbium (Yb3+) ions, optical gains at wavelengths of 1550, 980, and 1067 nm are achieved in NaYF4: Er3+, and Yb3+ nanoparticles‐doped polymer waveguides under excitation of low‐power light‐emitting diodes (LEDs) instead of 976 or 1480 nm semiconductor laser as pump sources. The optical gains at 1550, 980, and 1067 nm are demonstrated in five waveguide structures: active‐rectangular, evanescent‐field with and without an aluminium (Al) reflector, and dual‐active hybrid with and without an Al reflector. The maximum relative optical gains of 6.6, 4.0, and 3.8 dBcm−1 are realized at 1550, 1067, and 980 nm, respectively, in a 5 mm long dual‐active hybrid waveguide with cross‐section of 4 × 10 µm, and a ≈100 nm‐thick Al reflector grown under the lower cladding layer under excitation of a 395 nm LED. This work proves the feasibility of using a low‐cost LED to realize multi‐wavelength amplification in a dense wavelength‐division multiplexing system and is thus valuable for the development of complex multi‐functional photonic‐integrated‐module mixed‐band optical communication systems.

Measurement of nano molar ammonium with a cyclic olefin copolymer microchip and low-power LED

In oligotrophic regions, ammonium (NH4+) concentrations can be below 50 nM, however, few existing instruments can measure below this level with high confidence. This work, based on the o-pthaldialdehyde (OPA) fluorescence assay, is applied to measure nanomolar NH4+ in a novel optofluidic Cyclic Olefin Copolymer (COC) microchip using a low-power (20 mW) Light Emitting Diode (LED) as the excitation source. The optical arrangement was first modeled using ray tracing software to determine the initial detection volume size. Ammonium standards made with artificial seawater of 5 nM to 1000 nM, were run in triplicates. The limit of detection (LOD) obtained was 1.5 nM (3 x σ of the blank) or a LOD of 15 nM when the y-intercept and the vertical variation of each measured concentration on the calibration curve were taken into consideration (y-intercept +3. S y/x). Precision at 5 nM and 1000 nM was 3.3% and 0.5% respectively. The optofluidic system was also compared to an off-the-shelf fluorometer (Jasco FP2020) and an existing high-resolution shipboard analyser using five different standard concentrations. The LOD and the ammonium concentrations uncertainty for the Jasco FP2020, shipboard analyser, and current microsystem were 217 nM, 39 nM, and 15 nM and ± 232 nM, ± 48 nM, and ± 16 nM respectively. The optical setup was also validated using real samples from the Atlantic. This optical design, without optical fibres, makes the system simple and suitable for use with other fluorescent assays when compact, rugged, low-cost, and low-power consumption instrumentation is required.

Low-power blue LED and red laser effects on plasmid DNA, survival, and photolyase mRNA levels in Escherichia coli cultures

Low-power lasers and light-emitting diodes (LEDs) are used for photobiomodulation therapy, but the photobiological effects on DNA repair mechanisms in bacteria cells are disputed yet. This work aimed to evaluate the induction of DNA damages in plasmids, bacterial survival and proliferation, and photolyase mRNA levels in E. coli cultures exposed to low-power blue LED and red laser, followed by ultraviolet c (UVC) radiation. Aliquots of pUC19 plasmids and E. coli C600 cultures were exposed to low-power blue LED (470 nm) and red laser (658 nm) at different fluences. Other E. coli C600 cultures were exposed to UVC radiation after exposure to low-power blue LED and red laser. After irradiations, plasmids were submitted to agarose gel electrophoresis to evaluate DNA damage, bacterial cultures were spread onto Petri dishes content rich medium and incubated to evaluate bacterial survival and proliferation, and photolyase mRNA levels in bacterial cells were evaluated by reverse transcription-quantitative polymerase chain reaction. The results suggest that exposure to blue and red lights emitted from low-power LEDs and lasers does not cause DNA strand breaks in bacterial plasmids and does not alter the survival and mRNA levels from photolyase gene in E. coli cells, but increases bacterial survival and proliferation in E. coli cultures exposed to UVC radiation depending on LED and laser fluences.

High-Gain of NdIII Complex Doped Optical Waveguide Amplifiers at 1.06 and 1.31µm Wavelengths Based on Intramolecular Energy Transfer Mechanism.

Chelate phosphine oxide ligand (9,9-dimethyl-9H-xanthene-4,5-diyl) bis (diphenylphosphineoxide) (XPO) is prepared as a neutral ligand to synthesize complex Nd (TTA)3 (XPO) (TTA = 2-thenoyltrifluoroacetone). An appropriate energy gap between the XPO and TTA ligands, which can support two additional energy transfer routines from the first excited triplet state (T1 ) energy level of the XPO to that of the TTA, improves energy transfer in the Nd complex. Based on intramolecular energy transfer mechanism, optical gains at 1.06 and 1.31µm are demonstrated in Nd (TTA)3 (XPO)-doped polymer waveguides with the excitation of low-power light-emitting diodes (LEDs) instead of semiconductor lasers as pump sources. Using the vertical top-pumping mode of a 365nm LED, relative gains of 22.5 and 8.4dBcm-1 are obtained at 1.06 and 1.31µm, respectively, in a 0.2 cm long embedded waveguide with a cross-section of 8×5µm2 . The active core layer is Nd (TTA)3 (XPO)-doped SU-8 polymer. Moreover, relative gains are achieved in evanescent-field waveguide with a cross-section of 6×4µm2 . The 21.0 and 5.6dBcm-1 relative gains are achieved at 1.06 and 1.31µm, respectively, with a net gain of 13.8±0.3dBcm-1 obtained at 1.06µm in a 0.9 cm long SU-8 waveguide with Nd (TTA)3 (XPO)-doped polymethylmethacrylate as upper cladding.

Photoionization cross section of first excited state of lithium

We report the accurate quantitative measurements of the photoionization (PI) cross section of lithium-7 confined in a magneto-optical trap (MOT). The losses from the MOT induced by radiation of the low-power light-emitting diodes (LEDs) are measured as a function of the photoionizing radiation intensity. On the basis of these measurements, the PI cross section from the 2P3/2 excited state of lithium is evaluated for three different LEDs. The PI cross sections of lithium from the 2P3/2 state at 259, 280, 307 nm are determined to be (5.4 ± 0.4), (8.1 ± 0.8) and (9.5 ± 1.1) Mb respectively. Accuracy of our measurements is better than that of previous reported results. The semiclassical calculations taking into account the fine structure of the first excited state of lithium are performed. Our values are in good agreement with experimental results earlier reported and are consistent with the theoretical data.

Electromagnetic Interference Characteristics and Reduction Using CISPR11 for a Medical Light Emitting Diode Drive DCDC Buck Converter

Recently, many low-power LED (Light Emitting Diode) lighting fixtures that can contribute to a low-carbon society have been installed in clinical settings. However, since Alternating Current (AC) voltage cannot be used directly for LED devices, Direct Current (DC) voltage must be applied LED devices. For this reason, it is necessary for the LED equipment to install an ACDC power converter. A buck converter as an ACDC power converter is applied to the LED equipment, but Electromagnetic Interference (EMI) radiated from it has a strong influence on the wireless communication of a medical place. In particular, EMI radiated emission to medical telemeter systems using wireless communication becomes a significant problem of biomedical signal discontinuations. To investigate the EMI radiated strength, it must be measured using CISPR11 medical equipment international standard (International Special Committee on Radio Interference) on Limits and methods of measurement. This paper is focused on the LED drive DC power converter EMI radiated emission. The CISPR11 measurement EMI disturbance characteristics when a buck type current control DCDC buck converter circuit is used for the lighting of an LED device are shown. It is reported experimental results of EMI radiated emission characteristics improvement by changing the input and output circuit constants of the proposed circuit. Moreover, it is shown that can reduce to the floor noise level (background noise) when an output capacitor is inserted without an input filter.

NIR Irradiation Based on Low-Power LED Drive Module Design for Fat Reduction.

In this study, we designed a low-power visible ray (V) drive module based on a light-emitting diode (LED) to initiate fat reduction using light source irradiation. A chemical phantom of muscle and fat was fabricated, and the performance of the proposed LED drive module was tested using this chemical phantom. The LED light source could reduce fat by irradiating the skin 4–5 cm deep. The device exhibits a negative feedback and parallel amplification to maintain a stable circuit based on low-power consumption. Muscles have a high-water content and low impedance, whereas fats have a low water content and significant salt content. Therefore, fat exhibits high impedance. Chemical phantoms were fabricated according to these impedance values, and the fat reduction effect using the LED circuits was analyzed. When the fat phantom was irradiated by the light source, the fat impedance lowered, and we confirmed that fat reduction could be obtained. This study is expected to be applicable to family medicine and weight management health care.

Impact of thermal interface material on luminous flux curve of InGaAlP low-power light-emitting diodes

Purpose One major problem in the lighting industry is the thermal management of the devices. Handling of thermal resistance from solder point to the ambiance of the light-emitting diode (LED) package is linked to the external thermal management that includes a selection of the cooling mode, design of heatsink/substrate and thermal interface material (TIM). Among the significant factors that increase the light output of the of the LED system are efficient substrate and TIM. In this work, the influence of TIM on the luminous flux performance of commercial indium gallium aluminium phosphide (InGaAlP) low-power (LP) LEDs was investigated. Design/methodology/approach One batch of LEDs was mounted directly onto substrates which were glass-reinforced epoxy (FR4) and aluminium-based metal-core printed circuit boards (MCPCBs) with a dielectric layer of different thermal conductivities. Another batch of LEDs was prepared in a similar way, but a layer of TIM was embedded between the LED package and substrate. The TIMs were thermally conductive epoxy (TCE) and thermally conductive adhesive (TCA). The LED parameters were measured by using the integrated system of thermal transient tester (T3Ster) and thermal-radiometric characterization of LEDs at various input currents. Findings With the employment of TIM, the authors found that the LED’s maximum luminous flux was significantly higher than the value mentioned in the LED datasheet, and that a significant reduction in thermal resistance and junction temperature was revealed. The results showed that for a system with low thermal resistance, the maximum luminous flux appeared to occur at a higher power level. It was found that the maximum luminous flux was 24.10, 28.40 and 36.00 lm for the LEDs mounted on the FR4 and two MCPCBs, respectively. After TCA application on the LEDs, the maximum luminous flux values were 32.70, 36.60 and 37.60 lm for the FR4 and MCPCBs, respectively. Moreover, the findings demonstrated that the performance of the LED mounted on the FR4 substrate was more affected by the employment of the TIM than that of MCPCBs. Research limitations/implications One of the major problems in the lighting industry is the thermal management of the device. In many low-power LED applications, the air gap between the two solder pads is not filled up. Heat flow is restricted by the air gap leading to thermal build-up and higher thermal resistance resulting in lower maximum luminous flux. Among the significant factors that increase the light output of the LED system are efficient substrate and TIM. Practical implications The findings in this work can be used as a method to improve thermal management of LP LEDs by applying thermal interface materials that can offer more efficient and brighter LP LEDs. Using aluminium-based substrates can also offer similar benefits. Social implications Users of LP LEDs can benefit from the findings in this work. Brighter automotive lighting (signalling and backlighting) can be achieved, and better automotive lighting can offer better safety for the people on the street, especially during raining and foggy weather. User can also use a lower LED power rating to achieve similar brightness level with LED with higher power rating. Originality/value Better thermal management of commercial LP LEDs was achieved with the employment of thermal interface materials resulting in lower thermal resistance, lower junction temperature and brighter LEDs.

Looking Through Paintings by Combining Hyper-Spectral Imaging and Pulse-Compression Thermography.

The use of different spectral bands in the inspection of artworks is highly recommended to identify the maximum number of defects/anomalies (i.e., the targets), whose presence ought to be known before any possible restoration action. Although an artwork cannot be considered as a composite material in which the zero-defect theory is usually followed by scientists, it is possible to state that the preservation of a multi-layered structure fabricated by the artist’s hands is based on a methodological analysis, where the use of non-destructive testing methods is highly desirable. In this paper, the infrared thermography and hyperspectral imaging methods were applied to identify both fabricated and non-fabricated targets in a canvas painting mocking up the famous character “Venus” by Botticelli. The pulse-compression thermography technique was used to retrieve info about the inner structure of the sample and low power light-emitting diode (LED) chips, whose emission was modulated via a pseudo-noise sequence, were exploited as the heat source for minimizing the heat radiated on the sample surface. Hyper-spectral imaging was employed to detect surface and subsurface features such as pentimenti and facial contours. The results demonstrate how the application of statistical algorithms (i.e., principal component and independent component analyses) maximized the number of targets retrieved during the post-acquisition steps for both the employed techniques. Finally, the best results obtained by both techniques and post-processing methods were fused together, resulting in a clear targets map, in which both the surface, subsurface and deeper information are all shown at a glance.

LED-based opto-wetting and fluidic transport for droplet mixing

Light energy is utilized as an extensive tool for actuation of fluid flow in microfluidic devices. We report a novel method of droplet actuation using LED (light-emitting diode) that can be utilized for microfluidic mixing applications. This low power LED which emits light of peak wavelength 395 nm delivering luminous power of less than 300 millicandela (mcd) was used to create an interfacial tension gradient on solid–liquid interface containing photoresponsive molecule of azobenzene (C12H10N2). LED-induced photoisomerization of azobenzene creates a spatial gradient in interfacial energy on the solid–liquid interface, which enhances the droplet movement. The concept of LED-enhanced fluidic actuation was demonstrated using droplets of water, urine, blood serum over photoresponsive substrate. The substrates were prepared by coating the surface of silicon substrate with azobenzene dissolved in silicone resin solution. Detailed experimental characterization of LED-actuated droplet velocity was performed, where the effect of parameters such as frequency of light actuation, droplet volume, concentration of azobenzene was evaluated. Droplet transport of DI water (de-ionized) of volume 60 µL was achieved at a velocity of 160 µm/s corresponding to LED actuation frequency of 1 Hz. In vitro quantification of blood calcium and urine pH was performed using fabricated chip scale opto-wetting platforms. The proposed work could be useful in the development of droplet microfluidic chips, where combinatorial mixing can be achieved using an array of LEDs.

Comparative Analysis Between Water-Cooled and Air-Cooled Heat Dissipation in a High-Power Light-Emitting Diode Chipset

With a substantial increase in thermal power density, the operating temperature of high-power light-emitting diodes (LEDs) rises rapidly, exerting a notable effect on chipsets’ performance. A water-cooled microchannel radiator and an air-cooled radiator are proposed to solve this problem. The effects of key factors of both radiators on heat dissipation in a high-power LED chipsets, and general comparisons between each method, are analyzed via Fluent. The simulation results indicate that heat dissipation from the water-cooled microchannel radiator is readily affected by the microchannel’s flow rate and aspect ratio. A larger flow rate and larger aspect ratio favor improved heat dissipation in the water-cooled microchannel radiator. Heat dissipation in the air-cooled radiator is related to volumetric flow rate, rib number, rib height, rib thickness, and substrate thickness. A larger volumetric flow rate, rib number, and rib height favor heat dissipation in the air-cooled radiator. However, there is a critical thickness value: if the thickness is less than the critical value, heat dissipation is greatly affected by rib thickness and substrate thickness, if the thickness is larger than the critical value, the influence is insignificant. The high-power LED chipsets’ temperature is also related to the insulating substrate’ input power and thermal conductivity. A large input power leads to a substantial increase in temperature, and larger thermal conductivity of the insulating substrate minimizes temperature increase in the high-power LED chipsets. When comparing the two radiators, results show an air-cooled radiator should be used in low-power LED chipsets. When an air-cooled radiator cannot satisfy the chipset’s needs, a water-cooled microchannel radiator should be utilized.

Nonisolated Single-Switch Two-Channel LED Driver with Simple Lossless Snubber and Low-Voltage Stress

In two-channel light-emitting diode (LED) driver, capacitive-current-balancing method is the simplest and the most effective way to equally balance the current in each channel due to its simplicity. As a result, the capacitive balancing method was used with flyback or tapped-boost converters in low-power LED applications. Since flyback and tapped-boost converters suffer from a snubber loss and a high-voltage stress on the switching devices, conventional approaches use additional passive components, resulting in the limitations on the cost and power density. In this paper, a new converter topology for low-power two-channel LED application has been proposed. The proposed converter uses the blocking capacitor and the output capacitor as a snubber capacitor so that it has a low-voltage stress without using the additional components. Although the blocking capacitor plays a role as a snubber capacitor, the current balancing characteristic is still preserved. Furthermore, the proposed converter has a high efficiency since it minimizes the number of semiconductor components in the current paths. The effectiveness of the proposed converter has been verified with an offline 3.3 Vdc input and 11.55 W rated output prototype.

Influence of thermal interface material on thermal performance of InGaAlP thin-film SMD LED mounted on different substrate packages

PurposeProper thermal management is a key to improve the efficiency and reliability of light-emitting diodes (LEDs). This paper aims to report the influence of applying thermally conductive materials on thermal performance of indium gallium aluminum phosphide (InGaAlP)-based thin-film surface-mounted device (SMD) LED.Design/methodology/approachThe LED thermal and optical parameters were determined using the combination of thermal transient tester (T3Ster) and thermal and radiometric characterization of power LEDs (TeraLED) instruments. The LED was mounted on FR4, 2W and 5W aluminum (Al) package substrates. Measurements were carried out by setting different boundary conditions: air between LED package and substrate and using thermally conductive epoxy (TIM A) and adhesive (TIM B) of thermal conductivity 1.67 and 1.78 W/mK, respectively.FindingsFor LED mounted on FR4 package, the total real thermal resistance is improved because of TIM B by 6 and 9 per cent at 50 and 100 mA, respectively. Likewise, the relative decrease in total thermal resistance of LED on 2W Al package is about 9 and 11 per cent. As well, for LED mounted on 5W Al package, the total real thermal resistance is reduced by 2 and 4 per cent.Originality/valueNo much work can be found in the literature on thermal interface material effects on thermal performance of low-power SMD LED. This work can assist in thermal management of low-power LEDs.

A Highly Efficient Coupled-Inductor SEPIC Topology Based PFC DC–DC Converter for Low Power LED Lighting Systems

ABSTRACTThis paper deals with the design, simulation, and implementation of a single-stage single ended primary inductance converter (SEPIC) power factor correction (PFC) converter-based light emitting diode (LED) driver useful to operate for wide supply voltage variations. The proposed non-isolated SEPIC converter has been chosen to operate in discontinuous conduction mode (DCM) using pulse frequency modulation (PFM) control scheme to control output current through an LED lamp string. The primary focus of this work is to develop an efficient power converter with improved power quality performances for low power LED lighting systems. The modeling, simulation, and implementation of the proposed driver have been carried out for a 28 W LED string load. To confirm the design of the proposed driver, various power quality performance parameters are analyzed which are found well within the norms of international standard IEC 61000-3-2 of class C equipment throughout the universal AC mains.

Variation of thermal resistance with input current and ambient temperature in low-power SMD LED

PurposeThermal behavior of light-emitting diode (LED) device under different operating conditions must be known to enhance its reliability and efficiency in various applications. The purpose of this study is to report the influence of input current and ambient temperature on thermal resistance of InGaAlP low-power surface-mount device (SMD) LED.Design/methodology/approachThermal parameters of the LED were measured using thermal transient measurement via Thermal Transient Tester (T3Ster). The experimental results were validated using computational fluid dynamics (CFD) software.FindingsAs input current increases from 50 to 90 mA at 25°C, the relative increase in LED package (ΔRthJS) and total thermal resistance (ΔRthJA) is about 10 and 4 per cent, respectively. In addition, at 50 mA and ambient temperature from 25 to 65°C, the ΔRthJS and ΔRthJA are roughly 28 and 22 per cent, respectively. A good agreement between simulation and experiment results of junction temperature.Originality/valueMost of previous studies have focused on thermal management of high-power LEDs. There were no studies on thermal analysis of low-power SMD LED so far. This work will help in predicting the thermal performance of low-power LEDs in solid-state lighting applications.

Removal of dibutyl phthalate from aqueous environments using a nanophotocatalytic Fe, Ag-ZnO/VIS-LED system: modeling and optimization

ABSTRACTAn (Fe, Ag) co-doped ZnO nanostructure was synthesized by a simple chemical co-precipitation method and used for the degradation of dibutyl phthalate (DBP) in aqueous solution under visible light-emitting diode (LED) irradiation. (Fe, Ag) co-doped ZnO nanorods were characterized by powder X-ray diffraction, Fourier transform infrared spectroscopy, UV–VIS diffuse reflectance spectroscopy, elemental mapping, Field emission scanning electron microscopy, transmission electron microscope and Brunauer–Emmett–Teller surface area analysis. A Central Composite Design was used to optimize the reaction parameters for the removal of DBP by the (Fe, Ag) co-doped ZnO nanorods. The four main reaction parameters optimized in this study were the following: pH, time of radiation, concentration of the nanorods and initial DBP concentration. The interaction between the four parameters was studied and modeled using the Design Expert 10 software. A maximum reduction of 95% of DBP was achieved at a pH of 3, a photocatalyst concentration of 150 mg L−1 and a DBP initial DBP concentration of 15 mg L−1. The results showed that the (Fe, Ag) co-doped ZnO nanorods under low power LED irradiation can be used as an effective photocatalyst for the removal of DBP from aqueous solutions.

Modeling Spectra of Low-Power SMD LEDs as a Function of Ambient Temperature

The information of spectral changes with various parameters is a key for optimizing the performance and thus improving long-term reliability of light-emitting diodes (LEDs) in solid-state lighting applications. In this paper, the extension of spectrum model was used to estimate the spectral flux of indium gallium aluminum phosphide (InGaAlP)-based low-power surface-mounted device (SMD) LEDs. The spectra and photometric parameters of LED packages were measured at several ambient temperatures to test the spectrum model extension. The spectrum model is constructed at 298 K to predict the spectral fluxes of the LED at any ambient temperature. Carrier temperature, peak frequency, and bandgap energy variations with ambient temperature are included in this extension. The agreement between the measured and theoretical results of spectrum, luminous flux, and International Commission on Illumination (CIE) color coordinates validates the extended spectral model for low-power LEDs.

Antibacterial and cytotoxic effects of photoexcited Au clusters via blue high-power or white low-power light-emitting diode irradiation

Antibacterial and cytotoxic effects of photoexcited Au clusters via blue high-power or white low-power light-emitting diode irradiation

Plasmonic phototherapy of gold nanoparticles with Light Emitting Diode

Plasmonic Photo therapy (PPT) is a developing treatment modality for premalignant and malignant conditions. In this study, Gold nanospheres of 30 nm chose as potential sensitizer based on their pros and cons. Green Light Emitting Diode (LED) with 530nm of 30mW used as irradiation source. The cytotoxic effect of 30 nm GNPs based on the concentration and time was studied with MTT assay. In PPT, we study the cell death mechanism with non-coherent low power LED with GNP by photo irradiation study in Vero, Hela and Hep 2 cell lines. Post therapeutic changes in normal Vero and malignant Hela and Hep 2 cell lines were also observed for 2 ,24 and 48 hours. We observed localized apoptotic/secondary necrosis in irradiated spot, leading to irreversible cell. The viability and cell division of non-irradiated cells around irradiated spot was observed microscopically and by MTT assay. In PPT, fluence and GNP concentration were optimized since they perform crucial role in the mode of cell death. In this study we hypothesized that; plasmonic phototherapy leads to apoptosis with green LED of 30mW with 30nm GNPs.

Influence of light on the adsorption processes during interaction between reducer gases and a SnO2 film

The influence of the light of a low-power light-emitting diode on the adsorption processes in SnO2 sensor layers of test structures of gas sensors has been analyzed. It is established that the optical activation of SnO2 surface induces an additional peak of gas sensitivity at temperatures that are lower than the temperature of maximum gas sensitivity of the sensor without illumination. The results indicate that there are two mechanisms of light stimulation of gas adsorption.