Light-emitting Diode Light Source Research Articles

Temperature rises in the round window caused by various light sources during insertion of rigid endoscopes: an experimental animal study.

The instruments used in endoscopic surgery include rigid endoscopes of different diameters and angles, sources of light and monitors. In this study, we explored temperature rises in the round window caused by insertion of rigid endoscopes of different diameters into the middle ear; the endoscopes were fitted with different light sources. An experimental animal study. We subjected seven guinea pigs to simulate otological surgery at room temperature. We monitored body temperatures, along with temperature rises caused by the use of 0° rigid endoscopes of diameters 3 or 4 mm, fitted with light sources including a halogen light, a light-emitting diode (LED) and a xenon light. Data were collected every second from a sensor placed in the round window. An experimental study on 7 guinea pigs. Rise of the temperature on round window. Rigid endoscopes caused the temperature of the tympanum to rise when xenon and halogen light sources were used, regardless of endoscope diameter. However, the temperature rise was less when a LED light source was employed. The endoscopic instruments used in middle ear surgery caused the temperature of the round window to rise. The rise varied with endoscope diameter and the type of light source used.

Thermal analysis of chip-on-flexible LED packages with Cu heat sinks by SnBi soldering

Purpose – The purpose of this paper is to discuss the possibility of using soldering process for the bonding of chip-on-flexible (COF) light-emitting diode (LED) packages to heat sinks. The common bonding materials are thermal conductive adhesives. For thermal performance and reliability concerns, Tin-Bismuth (SnBi) lead-free solder paste was used for the connection of the COF packages and the Cu heat sinks by a soldering process in this study. Meanwhile, the geometrical effect of the SnBi solder layer on the thermal performance was also investigated. Design/methodology/approach – The effects of the bonding materials and the area of the solder layers on the thermal performance of the LED modules were investigated by finite element simulation and experimental tests. Findings – The SnBi soldered modules show much lower thermal resistance at the bonding layers than the adhesive-bonded LED module. Vertical heat transfer from the LED chips to the heat sinks is the primary heat dissipation mode for the SnBi soldered modules. Thus, the LED module with local solder layer shows similar LED thermal performance with the full-area soldered module. Meanwhile, the local soldering process decreases the possibility to form randomly distributed defects such as the large area voids and residue flux in the solder layers. Research limitations/implications – The research is still in progress. Further studies mainly focus on the reliability of the samples with different bonding materials. Practical implications – COF package is a new structure for LED packages. This study provides a comparison between SnBi solder and adhesive material on the thermal performance of the LED. Meanwhile, the authors optimized the geometrical design for the solder layer. The study provides a feasible bonding process for COF packages onto heat sinks. Originality/value – This study provides a soldering process for the COF LED packages. The thermal performance of the LED light source was improved significantly by the new process.

Light source design for spectral tuning in biomedical imaging.

We propose an architecture with a remote phosphor-based modular and compact light-emitting diode (LED) light source in a noncontact dermoscope prototype for skin cancer screening. The spectrum and color temperature of the output light can easily and significantly be changed depending on spectral absorption characteristics of the tissues being imaged. The new system has several advantages compared to state-of-the-art phosphor converted ultrabright white LEDs, used in a wide range of medical imaging devices, which have a fixed spectrum and color temperature at a given operating point. In particular, the system can more easily be adapted to the requirements originating from different tissues in the human body, which have wavelength-dependent absorption and reflectivity. This leads to improved contrast for different kinds of imaged tissue components. The concept of such a lighting architecture can be vastly utilized in many other medical imaging devices including endoscopic systems.

Complementary optimization method of freeform lens design for uniform illumination with extended light-emitting diode sources

A freeform lens design method based on energy mapping and complementary optimization approaches is proposed to achieve uniform illumination with extended light-emitting diode (LED) sources. This method is primarily derived from a simple source–a target energy mapping approach, while a complementary illuminance on the target plane is introduced to optimize the primary axisymmetric lens so that the profile of the lens can be reformed to produce uniform illumination when applying an extended LED source. By using this optimization method, the illuminance uniformity and optical efficiency of the lens can be improved, respectively, from 0.56 to 0.85 and from 92.4% to 94.3% for an LED light source with chip diameter of 8.9 mm, while the aspect ratio of the lens clear aperture to the source diameter is only 3.8.

Reflector designed for light-emitting-diode lighting source in three-dimensional space

Reflectors used for light-emitting-diode (LED) light source are designed in three-dimensional space to produce uniform illuminance effect. Reflector's surfaces are calculated by the source-target mapping method in Geometrical Optics. Ignoring scattering and absorption loss of the material, reflectors’ performances are investigated. The simulation results show that the light efficiency which is the ratio of light flux in the target surface to that from LED light source can reach above 95%. And the illuminance uniformity which is the ratio of minimum illuminance (min E) to average illuminance (ave E) also can reach above 95%. Finally, the array of reflectors is investigated and the result shows it still has good performance.

Atmospheric extinction in solar tower plants: absorption and broadband correction for MOR measurements

Abstract. Losses of reflected Direct Normal Irradiance due to atmospheric extinction in concentrated solar tower plants can vary significantly with site and time. The losses of the direct normal irradiance between the heliostat field and receiver in a solar tower plant are mainly caused by atmospheric scattering and absorption by aerosol and water vapor concentration in the atmospheric boundary layer. Due to a high aerosol particle number, radiation losses can be significantly larger in desert environments compared to the standard atmospheric conditions which are usually considered in ray-tracing or plant optimization tools. Information about on-site atmospheric extinction is only rarely available. To measure these radiation losses, two different commercially available instruments were tested, and more than 19 months of measurements were collected and compared at the Plataforma Solar de Almería. Both instruments are primarily used to determine the meteorological optical range (MOR). The Vaisala FS11 scatterometer is based on a monochromatic near-infrared light source emission and measures the strength of scattering processes in a small air volume mainly caused by aerosol particles. The Optec LPV4 long-path visibility transmissometer determines the monochromatic attenuation between a light-emitting diode (LED) light source at 532 nm and a receiver and therefore also accounts for absorption processes. As the broadband solar attenuation is of interest for solar resource assessment for concentrated solar power (CSP), a correction procedure for these two instruments is developed and tested. This procedure includes a spectral correction of both instruments from monochromatic to broadband attenuation. That means the attenuation is corrected for the time-dependent solar spectrum which is reflected by the collector. Further, an absorption correction for the Vaisala FS11 scatterometer is implemented. To optimize the absorption and broadband correction (ABC) procedure, additional measurement input of a nearby sun photometer is used to enhance on-site atmospheric assumptions for description of the atmosphere in the algorithm. Comparing both uncorrected and spectral- and absorption-corrected extinction data from 1-year measurements at the Plataforma Solar de Almería, the mean difference between the scatterometer and the transmissometer is reduced from 4.4 to 0.57 %. Applying the ABC procedure without the usage of additional input data from a sun photometer still reduces the difference between both sensors to about 0.8 %. Applying an expert guess assuming a standard aerosol profile for continental regions instead of additional sun photometer input results in a mean difference of 0.8 %. Additionally, a simulation approach which just uses sun photometer and common meteorological data to determine the on-site atmospheric extinction at surface is presented and corrected FS11 and LPV4 measurements are validated with the simulation results. For T1 km equal to 0.9 and a 10 min time resolution, an uncertainty analysis showed that an absolute uncertainty of about 0.038 is expected for the FS11 and about 0.057 for the LPV4. Combining both uncertainties results in an overall absolute uncertainty of 0.068 which justifies quite well the mean RMSE between both corrected data sets. For yearly averages several error influences average out and absolute uncertainties of 0.020 and 0.054 can be expected for the FS11 and the LPV4, respectively. Therefore, applying this new correction method, both instruments can now be utilized to sufficiently accurately determine the solar broadband extinction in tower plants.

Projection displays: New technologies, challenges, and applications

AbstractThe achievable color gamut and light output of projection displays based on light‐emitting diodes (LEDs), phosphor conversion, and lasers are discussed. The color appearance phenomena, colorfulness, and the Helmholtz–Kohlrausch effect are discussed in the context of LED and laser illumination of projection displays, as well as some pitfalls concerning the interpretation of the Helmholtz–Kohlrausch effect. Also the laser speckle phenomenon and the characterization of it are addressed. The importance of both the American National Standards Institute (ANSI) contrast and the sequential contrast of projectors, as well as the discrepancy between measured and perceived contrasts, are explained. Visibility criteria for contouring artifacts are explained and compared with new emerging electro‐optical transfer functions that are more adapted to this issue. Stereoscopic solutions and early prototypes of autostereoscopic multi‐view, super multi‐view projection displays, and electro‐holographic displays are discussed as well as the limiting factors of these systems in the context of display resolution, and LED and laser light sources.

Step-stress accelerated testing of high-power LED lamps based on subsystem isolation method

The lifetimes of high-power light-emitting diode (LED) lamps are investigated by step-stress accelerated test. The entire lamp is divided into three subsystems, namely, the LED light source, the driver, and the mechanical fixture. Step-stress accelerated tests are conducted on the LED light source only, which is placed in a thermal chamber and connected to other subsystems outside the aging furnace. Thus, the highest possible stress level can be reached for the LED light source. The reliability characteristics of the LED light source are analyzed based on the step-stress accelerated degradation test model. The fault tree and Monte Carlo algorithm are used to deduce the reliability of the entire LED lamp. The case study shows that the tested samples underwent similar degradation mechanisms under three reasonable stress levels and that the proposed procedure is fast and effective in accelerating the decay process of LED lamps. The predicted LED lamp lifetime is close to the value specified by the LED lamp manufacturer. The proposed subsystem isolation method can overcome the obstacle resulting from the significant difference between the breakdown stress limits of each subsystem.

Compact multi-channel surface plasmon resonance sensor for real-time multi-analyte biosensing.

A compact multi-channel surface plasmon resonance (SPR) biosensor is demonstrated based on a tablet as the measurement platform. The SPR biosensor employs a bundle of fiber-optic SPR sensors as the multiplexed sensing elements that are illuminated by a light-emitting diode (LED) plane light source and detected by a cordless camera. The multi-channel SPR biosensor was based on optical fiber components for precise, label-free and high-throughput detection without the use of complex, specialized or fragile instrumentation that would require optical calibration. The reference and control channels compensated for the fluctuation of the LED light source and the bulk refractive index, increasing the accuracy and reliability of the biosensor. The multi-channel SPR biosensor was applied for multi-analyte biosensing of immunoglobulin G (IgG) and concanavalin A (Con A). The channels functionalized with staphylococcal protein A (SPA) and ribonuclease B (RNase B) only showed relative intensity responses to their corresponding analytes. Moreover, the multi-channel SPR sensors responded to the specific detection of IgG and Con A with an approximately linear relative intensity response to the analyte concentration. Hence, multiple analytes were simultaneously and quantitatively detected with the multi-channel SPR biosensor. This compact, cost-effective multi-channel SPR biosensor is adapted for point-of-care tests, which are important in healthcare and environmental monitoring and for biomolecular interaction analysis.

Optimized lens design for small angle uniform illumination from an extended source

Based on the edge-ray principle of non-imaging optics, an optical design method for a lens producing small angle, uniform illumination from a high-power light-emitting diode light source has been developed. The energy correspondence between the light-emitting diode light source and the illuminance distribution on a target plane was established, and a number of discrete points for freeform profile curves which could achieve uniform illumination over a small angle were calculated and fitted to create a lens. Finally, simulations were performed using software. The influence of the size of light source on the emitting angle under uniform illumination was also investigated. The results show that the optical system can achieve uniform illumination with an extended source, the divergence angle being controlled within a minimum range by the optical design method.

White LED compared with other light sources: age-dependent photobiological effects and parameters for evaluation

Ergonomic science at work and living places should appraise human factors concerning the photobiological effects of lighting. Thorough knowledge on this subject has been gained in the past; however, few attempts have been made to propose suitable evaluation parameters. The blue light hazard and its influence on melatonin secretion in age-dependent observers is considered in this paper and parameters for its evaluation are proposed. New parameters were applied to analyse the effects of white light-emitting diode (LED) light sources and to compare them with the currently applied light sources. The photobiological effects of light sources with the same illuminance but different spectral power distribution were determined for healthy 4–76-year-old observers. The suitability of new parameters is discussed. Correlated colour temperature, the only parameter currently used to assess photobiological effects, is evaluated and compared to new parameters.

A Method for Reducing Blue Light Hazard from White Light-emitting Diodes Using Colourimetric Characterization of the Display

White light-emitting diodes (LEDs) are used as a light source in many liquid-crystal displays (LCDs), with blue light generated as a spectral distribution characteristic of white LEDs being potentially harmful to the human retina. We propose a method for reducing the blue light only by calibration and profiling without adjusting. Specifically, this paper attempted to verify the efficacy of colourimetric characterisation for reducing or controlling the blue light. Based on the test results of LCD monitors that use a variety of LED light sources, the white LED exhibited maximal blue light emission at 450 nm, and using colourimetric characterization reduced this emission by ~36%. The proposed method is a novel approach for examining the relationship between display technologies and the human retina.

Research on the Effect of Electrical Signals on Growth of Sansevieria under Light-Emitting Diode (LED) Lighting Environment.

The plant electrical signal has some features, e.g. weak, low-frequency and time-varying. To detect changes in plant electrical signals, LED light source was used to create a controllable light environment in this study. The electrical signal data were collected from Sansevieria leaves under the different illumination conditions, and the data was analyzed in time domain, frequency domain and time–frequency domain, respectively. These analyses are helpful to explore the relationship between changes in the light environment and electrical signals in Sansevieria leaves. The changes in the plant electrical signal reflected the changes in the intensity of photosynthesis. In this study, we proposed a new method to express plant photosynthetic intensity as a function of the electrical signal. That is, the plant electrical signal can be used to describe the state of plant growth.

High-Throughput Contact Flow Lithography.

High-throughput fabrication of graphically encoded hydrogel microparticles is achieved by combining flow contact lithography in a multichannel microfluidic device and a high capacity 25 mm LED UV source. Production rates of chemically homogeneous particles are improved by two orders of magnitude. Additionally, the custom-built contact lithography instrument provides an affordable solution for patterning complex microstructures on surfaces.

Phototherapy: A Simple and Safe Treatment for Neonatal Jaundice

Phototherapy: A simple and safe treatment for Neonatal Jaundice. Jaundice is a common finding in premature and full term newborns. Phototherapy has been widely used in the management of Neonatal unconjugated Hyperbilirubinemia for over five decades. Phototherapy devices include Fluorescent, Halogen, Fiberoptic or Light-Emitting Diode light sources. Safety issues and possible complications of phototherapy are discussed. It is a non invasive, safe and easily available therapy worldwide. This review will focus on the use of phototherapy in newborn nurseries.

Effects of type of light on mouse circadian behaviour and stress levels

Light is the principal synchronizing environmental factor for the biological clock. Light quantity (intensity), and light quality (type of light source) can have different effects. The aim of this study was to determine the effects of the type of light experienced from the time of birth on mouse growth, circadian behaviour and stress levels. We raised pigmented and albino mice under 24 h light-dark cycles of either fluorescent or white light-emitting diode (LED) light source during the suckling stage, and the animals were then exposed to various light environments after weaning and their growth rate, locomotor activity and plasma corticosterone concentration were measured. We found that the type of light the animals were exposed to did not affect the animals' growth rates or stress levels. However, we observed significant effects on the expression of the locomotor activity rhythm under low contrast light-dark cycles in pigmented mice, and under constant light in both albino and pigmented mice. These results highlight the importance of environmental light quality (light source) on circadian behavioural rhythms, and the need for close monitoring of light environments in animal facilities.

실리콘 서브 마운틴 기반의 LED 패키지 재료평가 및 신뢰성 시험

The light emitting diodes(LED) package of new structure is proposed to promote the reliability and lifespan by maximize heat dissipation occurred on the chip. We designed and fabricated the LED packages mixing the advantages of chip on board(COB) based on conventional metal printed circuit board(PCB) and the merits of Si sub-mount using base as a substrate. The proposed LED package samples were selected for the superior efficiency of the material through the sealant properties, chip characteristics, and phosphor properties evaluations. Reliability test was conducted the thermal shock test and flux rate according to the usage time at room temperature, high-temperature operation, high-temperature operation, high-temperature storage, low-temperature storage, high-temperature and high-humidity storage. Reliability test result, the average flux rate was maintained at 97.04% for each items. Thus, the Si sub-mount based LED package is expected to be applicable to high power down-light type LED light sources.

Curing efficiency of dual-cure resin cement under zirconia with two different light curing units.

Adequate polymerization is a crucial factor in obtaining optimal physical properties and a satisfying clinical performance from composite resin materials. The aim of this study was to evaluate the polymerization efficiency of dual-cure resin cement cured with two different light curing units under zirconia structures having differing thicknesses. 4 zirconia discs framework in 4 mm diameter and in 0.5 mm, 1 mm and 1.5 mm thickness were prepared using computer-aided design system. One of the 0.5 mm-thick substructures was left as mono-layered whereas others were layered with feldspathic porcelain of same thickness and ceramic samples with 4 different thicknesses (0.5, 1, 1.5 and 2.0 mm) were prepared. For each group (n=12) resin cement was light cured in polytetrafluoroethylene molds using Light Emitting Diode (LED) or Quartz-Tungsten Halogen (QHT) light curing units under each of 4 zirconia based discs (n=96). The values of depth of cure (in mm) and the Vickers Hardness Number values (VHN) were evaluated for each specimen. The use of LED curing unit produced a greater depth of cure compared to QTH under ceramic discs with 0.5 and 1 mm thickness (p<0.05).At 100μm and 300 μm depth, the LED unit produced significantly greater VHN values compared to the QTH unit (p<0.05). At 500 μm depth, the difference between the VHN values of LED and QTH groups were not statistically significant. Light curing may not result in adequate resin cement polymerization under thick zirconia structures. LED light sources should be preferred over QTH for curing dual-cure resin cements, especially for those under thicker zirconia restorations.

In vivo evaluation of battery-operated light-emitting diode-based photodynamic therapy efficacy using tumor volume and biomarker expression as endpoints.

In view of the increase in cancer-related mortality rates in low- to middle-income countries (LMIC), there is an urgent need to develop economical therapies that can be utilized at minimal infrastructure institutions. Photodynamic therapy (PDT), a photochemistry-based treatment modality, offers such a possibility provided that low-cost light sources and photosensitizers are available. In this proof-of-principle study, we focus on adapting the PDT light source to a low-resource setting and compare an inexpensive, portable, battery-powered light-emitting diode (LED) light source with a standard, high-cost laser source. The comparison studies were performed in vivo in a xenograft murine model of human squamous cell carcinoma subjected to 5-aminolevulinic acid-induced protoporphyrin IX PDT. We observed virtually identical control of the tumor burden by both the LED source and the standard laser source. Further insights into the biological response were evaluated by biomarker analysis of necrosis, microvessel density, and hypoxia [carbonic anhydrase IX (CAIX) expression] among groups of control, LED-PDT, and laser-PDT treated mice. There is no significant difference in the percent necrotic volume and CAIX expression in tumors that were treated with the two different light sources. These encouraging preliminary results merit further investigations in orthotopic animal models of cancers prevalent in LMICs.

LED measurement for development of a non-destructive detector of unsuitable chicken eggs in influenza vaccine production

In Japan, fertilised chicken eggs are used to produce influenza vaccines; however, some eggs die and then contaminate the vaccine stock solution, which causes large economic losses and raises health concerns. Therefore, a non-destructive test that allows distinction of normal and unsuitable chicken eggs was developed, first using visible and near-infrared (VNIR) spectroscopy and subsequently a light-emitting diode (LED) light source. Eggs were sampled from an egg farm, and each of the eggs categorised as either normal or unsuitable using candling. Linear discriminant analysis was applied using wavelength absorbance data to distinguish between normal and unsuitable eggs. All of the optical absorbance values of the normal eggs were found to be higher than those of unsuitable eggs. To reduce the production cost, LED lights and photodiodes were used as the light source and light receptors, respectively. A discrimination rate of 92.9% was obtained when LED was used as the light source.