Intensity Of Light-emitting Diodes Research Articles

Thermal transient evaluation and optical characterization of packaged light-emitting diodes

The study signifies the simultaneous thermal and optical characterizations of pre-molded and ceramic package light-emitting diodes (LEDs) at an increasing driving current. Results indicate that at high driving current produces greater luminous intensity and lower LED efficiency. Besides, pre-molded package LED exhibits better thermal management than ceramic package LED at package-level, and in contrast at board-level. Here, the packaging material properties and ratio of contacting surface areas are applied for description.

Photonic crystals and Bragg gratings for the mid-IR and terahertz spectral ranges

A method for the fabrication of 2D periodic structures by contact optical photolithography with image inversion is reported. The optical properties of photonic crystals and Bragg gratings for mid-IR and terahertz emitters are considered. The possibility of raising the integral emission intensity of light-emitting diodes for the mid-IR spectral range is demonstrated. The requirements to gratings for the output of terahertz emission generated by surface plasmons excited in layers of narrow-gap degenerate semiconductors with an accumulation layer are determined.

A multispectral LED array for the reduction of background autofluorescence in brain tissue

The presence of fixative-induced and cellular-derived artifactual autofluorescences (AAFs) presents a challenge in histological analysis involving immunofluorescence. We have established a simple and highly effective method for the reduction of AAFs that are ubiquitous in fixed mammalian brain and other tissues. A compact AAF-quenching photo-irradiation device was constructed using a commercially available light emitting diode (LED) array, cooling unit, and supporting components. The LED panel is comprised of an array of multispectral high intensity LEDs which serve as the illumination source for the photo-irradiation process. Rabbit and cat brain specimens of 5μm- and 40μm-thicknesses, respectively, were photo-irradiated for various durations. The AAFs were reduced to near tissue background levels after 24h of treatment for both deparaffinized and paraffinized rabbit brain specimens, and for the free-floating cat brain specimens. Subsequent immunofluorescence staining using primary antibodies against GFAP, NeuN, Iba-1, and MAP-2, and the corresponding Qdot® and Alexafluor® fluoroconjugates confirmed that the LED photo-irradiation treatment did not compromise the efficiency of the immunofluorescence labeling. The use of the device is not labor intensive, and only requires minimal tissue processing and experimental set-up time, with very low maintenance and operating costs. Finally, multiple specimens, in both slide and well-plate format, can be simultaneously photo-irradiated, thus, allowing for scalable batch processing.

YAG:Ce3+, Gd3+ nano-phosphor for white light emitting diodes

YAG:Ce3+, Gd3+ nano-phosphors were synthesised by the glycothermal method. The X-ray diffraction measurements showed that the samples can be well-crystallised at 600°C. The transition electron microscope showed that the particles have sizes mostly in the range between 35 and 100 nm. The YAG:Ce nano-phosphor had a wide emission band ranging from blue to yellow with a peak at 532 nm, due to the transition from the lowest 5d band to 2F7/2, 2F5/2 states of the Ce3+ ion. Red-shift of emission peak wavelength from 532 to 568 nm was achieved doping Gd3+ ions into the YAG:Ce3+ to substitute some Y3+ ions. White light emitting diodes (LEDs) were obtained by combining blue LED chip (InGaN-based 460 nm emitting) with (Y2.94− x Ce0.06Gd x )Al5O12 phosphor. As x has the value of 0.8, an intense white LED with good colour rendering of 86 was obtained.

Efeito da terapia LED (» = 945 ± 20 nm) de baixa intensidade sobre tecido epitelial de ratos diabéticos em processo de reparo

INTRODUCAO: O diabetes mellitus e uma condicao sistemica que pode causar retardo da resposta tecidual frente a uma lesao. Diversos estudos tem apontado o laser como importante ferramenta terapeutica para o auxilio do processo de reparo tecidual. Contudo, poucos estudos foram realizados com o emprego de LED (Light Emitting Diode). Assim, o objetivo deste trabalho foi analisar o efeito da terapia com LED (λ = 945 ± 20nm) de baixa intensidade sobre tecido epitelial de ratos diabeticos em processo de reparo. METODOS: Para tal, foi realizada a inducao de diabetes experimental em 20 ratos machos (Wistar), com administracao de 40mg/kg, por via endovenosa, de mono-hidrato de aloxana diluido em solucao tampao. Apos 14 dias, os animais foram submetidos a incisao tecidual na regiao dorsal, seguida de sutura e divididos em grupo-controle (GI e GIII, 3 e 7 dias pos-lesao, respectivamente), e grupo-tratado com LED (GII e GIV, 3 e 7 dias pos-lesao, respectivamente). Os animais do grupo tratado (n = 10) foram irradiados de forma transcutânea, em duas sessoes (30 minutos e 48 horas pos-lesao). RESULTADOS: O numero de fibroblastos foi significativamente maior no GIV em relacao ao GIII. CONCLUSAO: Considerando o aumento do numero de fibroblastos (analise quantitativa) e o adequado fechamento da lesao (analise qualitativa), pode-se concluir que houve um efeito positivo da terapia LED na regiao do infravermelho proximo sobre o processo de reparo, apos 7 dias de lesao tecidual em animais diabeticos (GIV).

A study of LED with surface photonic crystal structure fabricated by the nanoimprint lithography

Surface photonic crystal (PC) structure can improve the external quantum efficiency of light-emitting diode (LED). However, it is very difficult to fabricate large area and uniform nanometer photonic crystal structure in this field. In this paper, two-dimensional PC with hole-like structure is successfully transferred to the surface of gallium nitride LED (GaN-LED) by the mental-polymer double-layer mask dry etching technology combined with the nanoimprint lithography. The large area nanometer PC patterns with pore diameter of 240 nm and period of 450 nm are obtained. The results show that the photoluminescence peak intensity of LED with the PC structure is 7.2 times higher than that of the conventional LED.

Controlled electroluminescence of n-ZnMgO/p-GaN light-emitting diodes

Effective control of room-temperature electroluminescence of n-ZnMgO/p-GaN light-emitting diodes (LEDs) over both emission intensity and wavelength is demonstrated. With varied Mg concentration, the intensity of LEDs in the near-ultraviolet region is increased due to the effective radiative recombination in the ZnMgO layer. Furthermore, the emission wavelength is shifted to the green/yellow spectral region by employing an indium-tin-oxide thin film as the dopant source, where thermally activated indium diffusion creates extra deep defect levels for carrier recombination. These results clearly demonstrate the effectiveness of controlled metal incorporation in achieving high energy efficiency and spectral tunability of the n-ZnMgO/p-GaN LED devices.

Indoor Localization System based on Artificial Landmarks and Monocular Vision

This paper presents a visual localization approach that is suitable for domestic and industrial environments as it enables accurate, reliable and robust pose estimation. The mobile robot is equipped with a single camera which update sits pose whenever a landmark is available on the field of view. The innovation presented by this research focuses on the artificial landmark system which has the ability to detect the presence of the robot, since both entities communicate with each other using an infrared signal protocol modulated in frequency. Besides this communication capability, each landmark has several high intensity light-emitting diodes (LEDs) that shine only for some instances according to the communication, which makes it possible for the camera shutter and the blinking of the LEDs to synchronize. This synchronization increases the system tolerance concerning changes in brightness in the ambient lights over time, independently of the landmarks location. Therefore, the environment’s ceiling is populated with several landmarks and an Extended Kalman Filter is used to combine the dead-reckoning and landmark information. This increases the flexibility of the system by reducing the number of landmarks required. The experimental evaluation was conducted in a real indoor environment with an autonomous wheelchair prototype.

Evaluating Useful Life and Developing Replacement Schedules for LED Traffic Signals: Statistical Methodology and a Field Study

:LEDs (light-emitting diodes) have been widely adopted for use within traffic signals, recently replacing incandescent bulbs. LEDs degrade slowly – unlike incandescent bulbs that fail catastrophically. When the luminous intensity of LEDs falls below a pre-specified threshold, they pose danger to traffic. The long-term performance and degradation rates of LEDs have not been thoroughly studied in order to gain an understanding of their useful lives and appropriate replacement schedules. There exist many stochastic factors that affect LED degradation rates making their analysis complicated. This article provides a statistical methodology based on ordinary least-squares regression for measuring the useful life and the degradation rate of an LED signal, and presents details from a field study conducted in Missouri, U.S. Our results indicated that signal type, color, and manufacturer affect degradation, and therefore useful life should be calculated for each subgroup of LED traffic signals separately. Results of this research provide a much needed methodology for engineering managers in departments of transportation and local communities for replacing LEDs.

Comparison of the EMI Performance of LED PWM Dimming Techniques for LED Video Display Application

Light-emitting diode (LED) video displays enclose thousands of LEDs which create the resulting image. LED intensity is regulated using pulse width modulation (PWM). Though the individual LED current is small, the total current consumed is large. Simultaneous switching of a large number of LEDs dimmed by PWM can cause serious electromagnetic interference (EMI). Three LED PWM dimming techniques have been studied for potential EMI. Techniques represent different current pulse positioning in time: the aim of study was to compare the spectrum of current produced in LED video display power supply circuits when discussed techniques are used for pixel intensity control. It was assumed that the produced EMI is proportional to the power supply current. The power supply filter and transient load decoupling capacitors were not taken into account. The uniform and nonuniform pixels' intensities distribution within an image were assumed. Spectrum has been studied on a single pixel and the video display tile containing 16 × 32 LEDs. Resulting time diagrams and frequency responses are presented. The results indicate that, despite expected significant advantage of binary PWM methods, in realistic case all methods' performance is similar.

X-ray imaging using a consumer-grade digital camera

2 þ Computed radiography abstract The recent advancements in consumer-grade digital camera technology and the introduction of high- resolution, high sensitivity CsBr:Eu 2 þ storage phosphor imaging plates make possible a new cost- effective technique for X-ray imaging. The imaging plate is bathed with red stimulating light by high- intensity light-emitting diodes, and the photostimulated image is captured with a digital single-lens reflex (SLR) camera. A blue band-pass optical filter blocks the stimulating red light but transmits the blue photostimulated luminescence. Using a Canon D5 Mk II camera and an f1.4 wide-angle lens, the optical image of a 240 � 180 mm 2 Konica CsBr:Eu 2 þ imaging plate from a position 230 mm in front of the camera lens can be focussed so as to laterally fill the 35 � 23.3 mm 2 camera sensor, and recorded in 2808 � 1872 pixel elements, corresponding to an equivalent pixel size on the plate of 88 mm. The analogue-to-digital conversion from the camera electronics is 13 bits, but the dynamic range of the imaging system as a whole is limited in practice by noise to about 2.5 orders of magnitude. The modulation transfer function falls to 0.2 at a spatial frequency of 2.2 line pairs/mm. The limiting factor of the spatial resolution is light scattering in the plate rather than the camera optics. The limiting factors for signal-to-noise ratio are shot noise in the light, and dark noise in the CMOS sensor. Good quality images of high-contrast objects can be recorded with doses of approximately 1 mGy. The CsBr:Eu

Multi-wavelength spatial LED illumination based detector for in vitro detection of botulinum neurotoxin A activity

A portable and rapid detection system for the activity analysis of botulinum neurotoxins (BoNT) is needed for food safety and bio-security applications. To improve BoNT activity detection, a previously designed portable charge-coupled device (CCD) based detector was modified and equipped with a higher intensity more versatile multi-wavelength spatial light-emitting diode (LED) illumination, a faster CCD detector and the capability to simultaneously detect 30 samples. A FITC/DABCYL Förster Resonance Energy Transfer (FRET)-labeled peptide substrate (SNAP-25), with BoNT-A target cleavage site sequence was used to measure BoNT-A light chain (LcA) activity through the FITC fluorescence increase that occurs upon peptide substrate cleavage. For fluorescence excitation, a multi-wavelength spatial LED illuminator was used and compared to our previous electroluminescent (EL) strips. The LED illuminator was equipped with blue, green, red and white LEDs, covering a spectrum of 450–680 nm (red 610–650 nm, green 492–550 nm, blue 450–495 nm, and white LED 440–680 nm). In terms of light intensity, the blue LED was found to be ∼80-fold higher than the previously used blue EL strips. When measuring the activity of LcA the CCD detector limit of detection (LOD) was found to be 0.08 nM LcA for both the blue LED (2 s exposure) and the blue EL (which require ≥60 s exposure) while the limits of quantitation (LOQ) is about 1 nM. The LOD for white LED was higher at 1.4 nM while the white EL was not used for the assay due to a high variable background. Unlike the weaker intensity EL illumination the high intensity LED illumination enabled shorter exposure times and allowed multi-wavelength illumination without the need to physically change the excitation strip, thus making spectrum excitation of multiple fluorophores possible increasing the versatility of the detector platform for a variety of optical detection assays.

An Optimum Design and Fabrication of Focus Lens for High Intensity Light-Emitting Diodes

A maximum output intensity of high-power light-emitting diodes (LEDs) with high-efficiency focus lens is demonstrated. A commercial software package of Trace Pro and one-factor method are used to simulate the focus lens. The optimum parameters of focus-lens design are the radius curvature, cavity depth, and lens height are 2.75, 2.45, and 5.7 mm, respectively. For the fabrication of focus lens with injection molding, the optimum parameters are simulated by adapting Taguchi's method of the smaller-the better algorithm in a software package for Moldex 3D. By employing both optimum design and fabrication of the focus lens, a maximum peak intensity for 64.6 cd for a 1 W blue LED module was realized under a constant driving current of 320 mA and the voltage of 3.2 V. In comparison with a commercial focus lens used in high-power LEDs under the same test conditions, the high-power LEDs with proposed focus lens exhibits about 2–3 times improvement in the output intensity. This study may provide a practical guideline for design and fabrication of a high-efficiency focus lens used in high-intensity high-power LED modules.

A comparison of several nanoscale photocatalysts in the degradation of a common pollutant using LEDs and conventional UV light

A comparative study on the photocatalytic activities of four different catalysts, P-25 TiO 2, TiO 2 nanofibers, tin-doped TiO 2 nanofibers under UV light irradiation at 350 nm, and coumarin (C-343) coated TiO 2 nanofibers at 436 nm light emitting diodes (LED) is reported. Catalysts performance has been compared based on their reflectance spectrum and activity. A common water contaminant 4-chlorophenol was used as a substrate to compare the activity of the different catalysts under both direct and dye sensitized conditions. Results indicated that amongst the four different catalysts the activity of P-25 was the highest. However the activity of C-343 coated TiO 2 nanofibers in the LED (436 nm) based reactor was competitive. Identification of reaction intermediates implied that the reaction pathways under UV (band gap) and visible (dye sensitized) irradiation were different. Nonetheless, ring opening took place in all reactions with both maleic and dihydroxymaleic have been identified as intermediates. The study indicates that ordered arrays of TiO 2 irradiated by panels of arrays of low cost high intensity LEDs might be used for the design of reactors. The near monochromaticity, long life, and operation under direct currents are advantages of using LEDs.

An Intense Green/Yellow Dual-Chromatic Calcium Chlorosilicate Phosphor Ca3SiO4Cl2 : Eu2 + –Mn2 + for Yellow and White LED

A series of intense green/yellow phosphors was synthesized by a high-temperature solid-state reaction. Their luminescent properties were characterized by means of powder diffuse reflection, photoluminescence excitation and emission spectra, and lifetime and temperature-dependent emission spectra in the temperature range of 10–450 K. The phosphors show intense broad absorption bands between 250 and 450 nm, matching well with the near-ultraviolet (380–420 nm) emission band of InGaN-based chips, and exhibit two dominating bands situated at 512 and 570 nm, ascribed to the allowed transition of the ion and the transition of the ion, respectively. The lifetime of the ion decreases with increasing the concentration of the ion, strongly supporting an efficient energy transfer from to . By combining with near-ultraviolet InGaN chips, intense yellow light-emitting diodes (LEDs) with a much lower ultraviolet light leakage were successfully fabricated based on the phosphor, and intense white LEDs were made based on a blend of blue chlorophosphate phosphor and the green/yellow phosphor . The color coordinate, correlated color temperature , general color-rendering index , and luminous efficiency of the fabricated white LEDs are (0.3281, 0.3071), 6065 K, 84.5, and 11 lm/W, respectively.

Effect of Type of Light Curing Unit on Shear Bond Strength of Resin Composite.

Aims: To compare the shear bond strength (SBS) of composite bonded to dentin cured by three light curing units (LCUs), which are quartz tungsten halogen (QTH) and two types of light emitting diode (LED) machines. Materials and Methods: Buccal dentin of 90 upper premolars was exposed, prior to restorative procedure. Samples divided into 3 groups, restoration of each group cured by Astralis 5 [Austria], Top Light, [Taiwan] and Ultradent [USA]. Each group further subdivided into three subgroups. After bonding application, each subgroup of every group restored by one of 3 composites: Point 4™, Tetric and Degufill mineral. Composite applied and cured for 40 seconds. Samples thermocycled and loaded at tooth–composite interface. Results: Analysis of variance (ANOVA) with significance p < 0.05 followed by Duncan Multiple Range Test, showed that SBS of subgroups that cured by Ultradent (400 mW/cm2) was significantly higher than Astralis 5 (405 mW/cm2) and Top Light (141 mW/cm2). The SBS of Astralis 5 was significantly higher than Top Light. No significant differences found among subgroups those cured by same LCU. Conclusions: Shear bond strength of resin composite bonded to dentin is directly proportional with the light intensity. However, better result obtained by a high intensity LEDs compared with an equivalent intensity QTH–LCUs.

Characteristics of Green Light-Emitting Diodes Using an InGaN:Mg/GaN:Mg Superlattice as p-Type Hole Injection and Contact Layers

Mg-doped InGaN/GaN p-type short-period superlattices (SPSLs) are developed for hole injection and contact layers of green light-emitting diodes (LEDs). V-defect-related pits, which are commonly found in an InGaN bulk layer, can be eliminated in an InGaN/GaN superlattice with thickness and average composition comparable to those of the bulk InGaN layer. Mg-doped InGaN/GaN SPSLs show significantly improved electrical properties with resistivity as low as ∼0.35 ohm-cm, which is lower than that of GaN:Mg and InGaN:Mg bulk layers grown under optimized growth conditions. Green LEDs employing Mg-doped InGaN/GaN SPSLs for hole injection and contact layers have significantly lower reverse leakage current, which is considered to be attributed to improved surface morphology. The peak electroluminescence intensity of LEDs with a SPSL is compared to that with InGaN:Mg bulk hole injection and contact layers.

Solid-State Pressure-Tolerant Illumination for MBARI's Underwater Low-Light Imaging System

A significant amount of energy is consumed by the typical illumination systems of underwater vehicles. Attempts to utilize more efficient LED illumination underwater have been unsuccessful because the light-emitting diodes (LEDs) were coupled to a standard imaging system and they were not able to generate enough light to adequately illuminate the scene. In cases where the LEDs were grouped together, to provide more scene illumination, the lighting assembly was inefficient in size. The recent availability of high intensity LEDs provides a way to produce efficient and adequate lighting from a compact assembly. This paper covers the development of a deep ocean assembly based on these high intensity LEDs

Uncertainty evaluation for the spectroradiometric measurement of the averaged light-emitting diode intensity

An uncertainty evaluation is presented for the spectroradiometric measurement of the averaged LED intensity (ALI), which is a standardized photometric quantity of LEDs introduced by the Commission Internationale de l'Eclairage. Using a spectral irradiance standard lamp as a calibration source for the spectroradiometer, 12 uncertainty components are sorted out and their propagation formulated with correlations between the components taken into account. The procedure of uncertainty evaluation is demonstrated for four LED samples of different colors; red, green, blue, and white. The relative uncertainties of the ALI of the test samples are determined to be in a range from 4.1% to 5.5% (k=2), but most of their dominant uncertainty components turn out to be systematic and correlated. In conclusion, correlations between the uncertainty components critically affect the overall uncertainty of the LED measurement using a spectroradiometer.

Machine vision developments

PurposeTo review recent developments in machine vision hardware and techniques, as revealed in the Image Processing and Optical Technology Exhibition, 2006.Design/methodology/approachDifferent sections of the paper examine new cameras and their interfacing, smart cameras with DSP processors, a powerful framegrabber, high intensity light emitting diode (LED) lighting, and developments in teraherz sources and detection.FindingsSmart cameras now exist with greater processing speed than a PC. A new generic programming interface aims to ease the incompatibilities of digital cameras. Water cooling has produced a very intense and long life LED light, and a novel goniophotometer has no moving parts. Rapid advances are occurring in the field of terahertz imaging.Originality/valueProvides an update on machine vision technology for scientists and engineers generally, and a source of contact information for specialists to follow up where necessary.