General Light Source Research Articles

一般LED光源均匀配光的自由曲面菲涅耳透镜

一般LED光源均匀配光的自由曲面菲涅耳透镜

Recent Progress in Blue Phosphors: From Non-Thermal Quenching to Highly Efficient Phosphor

In the present era of solid-state lighting, white light-emitting diodes (WLEDs) have received enormous attention as general lighting source due to its energy efficiency and environmental friendly technology. However, the current high power WLED faces serious challenge of luminescence loss of phosphor due to the generation of heat under operation and at elevated temperature known as thermal quenching. Therefore, it is highly desirable to find new phosphors with high efficiency and thermal stability. Hence, our search for a new and efficient phosphor host, has led to the emergence of oxohalide/oxide host with very high PL and conversion efficiency. In this talk, some works from our laboratory on the recent progress in blue-emitting phosphors are summarized. In particular, new NASICON based blue-emitting phosphor shows negligible thermal quenching for WLED applications, which exhibited broad blue emission under near UV excitation and retains its luminescence at elevated temperature of 473 K. Also, some blue-emitting phosphors with their excellent optical properties are reported.1,2 References[1] S. J. Gwak, P. Arunkumar, and W. B. Im, J. Phys. Chem. C, Vol.118, pp. 2686-2692, 2014.[2] Y. H. Kim and W. B. Im, Opt. Lett., Vol.39, pp. 4887-4890, 2014. Figure 1

Solid-State Lighting: A Concise Review of the State of the Art on LED and OLED Modeling

This article presents an overview of technologies for solid-state lighting (SSL). In recent years, light-emitting diodes (LEDs) have developed characteristics desirable for lighting applications. The success of these light sources for general lighting depends on the system design, which comprises an understanding of electrical and photometrical characteristics under the temperature effect on device performance. This review focuses on the main theoretical models for the characterization of SSL devices, regarding the electrical and thermal aspects to reach the desired photometrical characteristic for a lighting system. An approach about inorganic LEDs and organic LEDs (OLEDs) will be presented along with the application of these devices in SSL systems.

Enabling a blue-hazard free general lighting based on candle light-style OLED.

Increasing studies report blue light to possess a potential hazard to the retina of human eyes, secretion of melatonin and artworks. To devise a human- and artwork-friendly light source and to also trigger a "Lighting Renaissance", we demonstrate here how to enable a quality, blue-hazard free general lighting source on the basis of low color-temperature organic light emitting diodes. With the use of multiple candlelight complementary emitters, the sensationally warm candle light-style emission is proven to be also drivable by electricity. To be energy-saving, highly efficient candle-light emission is demanded. The device shows, at 100 cd m-2 for example, an efficacy of 85.4 lm W-1, an external quantum efficiency of 27.4%, with a 79 spectrum resemblance index and 2,279 K color temperature. The high efficiency may be attributed to the candlelight emitting dyes with a high quantum yield, and the host molecules facilitating an effective host-to-guest energy transfer, as well as effective carrier injection balance.

Manufacturing of Cs3Sb Photocathode in Atmospheric Conditions

<TEX>$Cs_3Sb$</TEX> photocathode was formed by newly developed process and successive in-situ lighting devices were fabricated in a process chamber. R, G, and B phosphors were applied on the anode plate, respectively. Major parameters such as brightness, power consumption, and efficacy were measured. The wavelength of LED excitation source was 450 nm. Both high power and low power modes were applied in the measurement. Measurement values were clearly differentiated by the voltage application modes. The measured values of each parameter was good enough to be applied for general lighting source. The results showed that <TEX>$Cs_3Sb$</TEX> photocathode formed in atmospheric conditions was functioning as good as the photocathode formed in UHV conditions, and thus it could be applied to advanced lighting devices.

Organic Host Materials for Solution‐Processed Phosphorescent Organic Light‐Emitting Diodes

AbstractAs a new technology for flat‐panel displays and general lighting sources, solution‐processed phosphorescent organic light‐emitting diodes (PhOLEDs) unfurl a bright future, due to their merits of high quantum efficiency and easy fabrication. In recent years, great progress has been made in the device performance of solution‐processed PhOLEDs, by developing both high‐efficiency organometallic phosphors and novel solution‐processable organic host materials. This review highlights recently developed organic host materials for triplet guest emitters in solution‐processed PhOLEDs. The solution‐processable host materials are classified into three types – small molecule, dendrimer, and polymer – according to their molecular architecture and molecular weight. The material design concept and the relationships between the molecular structure, material properties and device performance are the focus of this discussion. A future strategy for the development of high‐performance solution‐processed host materials is proposed.

Practical Use and Calculation of CCT and Duv

Correlated color temperature (CCT) is often used to represent chromaticity of white light sources, but chromaticity is two-dimensional, and another dimension, the distance from the Planckian locus, is often missing. Duv is defined in ANSI C78.377 for this purpose but is not yet widely used. In this article, the use of a combination of CCT and Duv is proposed as an intuitive expression of chromaticity of white light sources for general lighting. In addition, this article presents practical calculation methods to calculate CCT and Duv, having sufficient accuracy, within an error of 1 K, in a wide range of chromaticity, from 1000 to 20,000 K in CCT and −0.03 to 0.03 in Duv.

ILight: Device-Free Passive Tracking Using Wireless Sensor Networks

In this paper, we study indoor passive tracking problem using wireless sensor networks, in which we assume that a target being tracked is clean, i.e., there is no any equipment carried by the target, hence, the tracking procedure is considered to be passive. We first show that received signal strength indicator and link quality indicator are not as effective as expected for passive detection (tracking) through our extensive testbed studies, and further propose to utilize light to track targets using WSNs. To the best of our knowledge, this is the first work, which studies the passive tracking problem in WSNs using light sensors and general light sources. We present a number of probability-based algorithms to study the moving patterns (properties) of targets being tracked. We design and implement our tracking system named as iLight consisting of 40 wireless sensor nodes and one base station. Through extensive experimental results, we show that iLight can track both single target and multiple targets efficiently.

Utilization of Solvothermally Grown InP/ZnS Quantum Dots as Wavelength Converters for Fabrication of White Light-Emitting Diodes

This work reports on a simple solvothermal synthesis of InP/ZnS core/shell quantum dots (QDs) using a much safer and cheaper phosphorus precursor of tris(dimethylamino)phosphine than the most popularly chosen tris(trimethylsilyl)phosphine. The band gap of InP QDs is facilely controlled by varying the solvothermal core growth time (4 vs. 6 h) with a fixed temperature of 150 degrees C, and the successive solvothermal ZnS shelling at 220 degrees C for 6 h results in green- and yellow-emtting InP/ZnS QD with emission quantum yield of 41-42%. The broad size distribution of as-synthesized InP/ZnS QDs, which appears to be inherent in the current solvothermal approach, is improved by a size-selective sorting procedure, and the emission properties of the resulting size-sorted QD fractions are investigated. To produce white emission for general lighting source, a blue light-emitting diode (LED) is combined with non-size-soroted green or yellow QDs as wavelength converters. Furthermore, the QD-LED that includes a blend of green and yellow QDs is fabricated to generate a white lighting source with an enhanced color rendering performance, and its electroluminescent properties are characterized in detail.

형광체 코팅에 따른 Remote Phosphor 구조의 백색 LED 패키지 특성 평가

We developed a package of remote phosphor structure having blue LED chips and phosphors physically separated, and the characteristics were evaluated according to different classifications of phosphor coatings. Remote phosphor was produced by screen printing coating on glass substrate with phosphor content rated paste and heat treatment. After mounting Remote phosphor, which has been classified according to number of coatings, on top of blue LED chips, luminous flux, luminous efficacy, CCT and CRI were measured. The measurement results showed the most suitable characteristics of white LED package as a general light source when the content rate of phosphor in Remote phosphor was 80 wt.% with 3 layers of coatings and thickness over .

Applying micro genetic algorithm to numerical model for luminous intensity distribution of planar prism LED luminaire

Several technological problems have to be resolved for LED to be used as a general purpose light source. For instance, LED luminaires have a property of high luminance due to a narrow beam angle and a small volume compared to general light sources. There are several differences between existing luminaires and the intensity distribution of an LED luminaire. An optical engineer has the challenging problem of designing a spatially extended and non-uniform light source. It is difficult for LED luminaires to obtain the target luminous intensity distribution required in a space, because the design process requires much trial and error. And the process also requires much design time. In this study, an optimization algorithm of a numerical model for luminous intensity distribution of planar LED luminaires was developed to find optimized prism angles. This algorithm would used the micro genetic algorithm technique which is the improved form of genetic algorithms. Also, this algorithm is capable of deriving the optimized angle of a prism to achieve the target luminous intensity distribution of planar prism LED luminaires. Therefore, the purpose of this study is to introduce a numerical model of a planar prism LED luminaire and to develop a optimization algorithm that is able to find an optimum luminaire optical design solution using the micro genetic algorithm.

Energy Star 기준에 따른 Omnidirectional LED 벌브의 전기적 광학적 특성 분석

An LED (light emitting diode) has the advantages of lower power consumption, energy saving, high efficiency, long lifetime, and environmental friendliness so that it has been getting the spotlight as a next-generation light source. Thus, the application range of an LED has been extended to various fields including indoor and outdoor lighting. Recently, the high efficient LED lighting has been developed, an LED has been extended its market rapidly every year and is expected to replace the general light source within near future. In this study were measured electrical and optical properties for 6 types of LED bulbs which are being developed to replace the general incandescent lamps, and were analysed under the standard of the omnidirectional lamp required by the Energy Star.

The PSD General Response Function

The general response of a 1-D position-sensitive detector (PSD) is derived by solving the Lucovsky equation in a fully general way. A general light source is divided into many sections in space domain and pulse elements in time domain. Each section is regarded as a plane-wave element and each pulse as a square-wave pulse. By virtue of the linear superposition of the Green function, the general response is regarded as the summation of respective responses to those elements. The response indicates that a PSD is a decaying photocurrent accumulator, both in space and time domains. Results discussed in this paper are quite in agreement with the facts and the conclusions from the previous papers. In addition, analysis on the alternating current (ac) response characteristics by virtue of the general response shows that there is a hysteretic oscillation in accord with the light intensity variation and that the response is insensitive to high-frequency ac light signals.

평면 프리즘 LED 조명기구 배광수치모델의 다양한 배광 제어를 위한 연구

There are several technological problems have to be resolved for LEDs to be used as a general purpose light source. In addition, there are several differences between existing luminaires and the general planer LED luminaire for the intensity distribution. Therefore, the optical engineer then faces the challenging a problem of designing for a spatially extended and non-uniform light source. In the previous studies on the optical design of luminaires, a lot of studies on reflectors and light source have been conducted but the ones on prisms and lenses are insufficient at present. This study developed the numerical model of planar prism LED luminaire to control luminous intensity distribution of LED luminaires. And this study presents an optical calculation process for the prism optical design of a planar prism LED luminaire and a comparison of the simulation results between the developed numerical model and Photopia 2.0 to verify the accuracy of the numerical model. In addition, this study showed a method for the control of various luminous intensity distribution from the developed numerical model.

A NADH-dependent fiber-optic biosensor for ethanol determination with a UV-LED excitation system

A fluorometric fiber-optic biosensor for ethanol determination was constructed and tested. An ultraviolet light emitting diode (UV-LED) was used as a fluorescence excitation source for nicotinamide adenine dinucleotide (NADH). The use of a UV-LED conferred the advantages of low power consumptions and the potential for portable application. The biosensor consists of a UV-LED based portable excitation system (λ=340nm), fiber optic spectrometer and an optical fiber probe with an alcohol dehydrogenase immobilized membrane. These instruments were connected using a Y-shaped optical fiber assembly. According to the experimental assessment, the power consumption was reduced to one percent of general UV light source. The measurement system was useful for 1.00–300μmolL−1 of NADH. EtOH measurement test was also carried out. The wide calibration range of the EtOH biosensor was 0.10–100.00mmolL−1, with high selectivity versus other chemical substances. The biosensing system is simplified and miniaturized by use of LED in compare with previous methods. For this advantage, the biosensing system is expected to be used for point-of-care testing applications or daily health care tests.

A general calculation of the 3-D disk of least confusion using skew ray tracing

A general and analytical method is proposed to determine the 3-D contour of the disk of least confusion (DLC) produced by an optical system for a point light source located at any arbitrary position in the object space. By using the skew ray tracing method, the sensitivity method, and the Jacobian matrix, we can analytically obtain the caustic and the marginal rays. Consequently, the DLC can be determined by the intersection of the obtained caustic and marginal rays. In addition, this proposed method covers common cases with special light sources, e.g. mutually parallel incident rays parallel to the optical axis, or a point light source located on the optical axis. This proposed methodology will be useful in the analysis of rays and in the design of optical systems with a general point light source. A general case is used as illustrative example to validate its applications.

A Long-Term Energy Saving Analysis on LEDs General Lighting in China

Based on survey of China's lighting products market and estimation of trends of LEDs technical innovation of general lighting, the paper has established a model to analyze the impacts on China's future lighting market and energy efficiency potential as LEDs appear to be a next generation of general lighting source. By doing scenarios analysis, the results of this study indicated that only 1% of LEDs contribution rate to the lighting market will be realized by 2018, while up to nearly 2.5% by 2020 under the baseline scenarios; for technology-breakthrough scenarios, 1% of LEDs contribution rate will be realized by 2015, increase to 14% by 2020; while under the price-breakthrough scenarios, LEDs will constitute 1% contribution rate to the general lighting market by 2013, two years earlier in comparison, due to the decreased price, the market penetration process will speed up and by 2015 and 2020 the contribution rate of LEDs to general lighting market will increase to 9% and 69% respectively. Meanwhile, the electricity saving effects of LEDs with regard to general lighting field will show up approximately by 2013, with electricity consumption increase from over 278.4 Twh for general lighting of 2005 to 398.2 Twh in 2020 under baseline scenario; while under the technology-breakthrough scenario, the consumption for lighting of 2020 will be 344.9 Twh, under price-breakthrough scenario, the figure will drop to 313.4 Twh instead. Therefore, in 2020 there will be an energy saving possibility of 53.4 Twh with regard to the technology-breakthrough scenario; meanwhile the price-breakthrough solution in comparison with the baseline has a considerable energy saving potential over 84.8 Twh.

Crosslinkable Hole‐Transport Layer on Conducting Polymer for High‐Efficiency White Polymer Light‐Emitting Diodes

Organic and polymer light-emitting diodes (LEDs) have been the subject of intensive investigation in recent years because of their potential as emissive elements for flat-panel displays and white-light sources for general lighting. As dualinjection devices, multilayer structures with discrete hole-injection layers (HILs) and/or hole-transport layers (HTLs), light-emitting layers (EMLs), and electron-transport layers (ETLs) are necessary for high efficiency, where these layers can be optimized, respectively, according to their functions. [1–3] For LEDs based on small molecules, it is rather straightforward to adopt this multilayer strategy via layer-bylayer vacuum deposition. However, for polymer-based LEDs, where solution-based casting or spin-coating is the basic way to form films, it is very challenging to form multilayer structures, because of solvent erosion of previously deposited layers during spin-coating. [4] To overcome this problem, a

A unified framework for scene illuminant estimation

Most existing illuminant estimation algorithms work with assumptions of specific source types (e.g. directional light source or point light source). The assumptions bring up two main limitations which significantly restrict their applicabilities: first, the prior knowledge about source types is needed; second, it can not handle complex scenes where multiple source types co-exist. In this paper, we develop a general light source model which is designed to model arbitrary light sources. With the general source model, we are able to estimate multiple illuminants of different types within a single unified framework. We use a plastic sphere to probe both diffuse and specular reflections of a scene. With specular reflections, we estimate geometric parameters of the illuminants by a novel ray tracing and matching algorithm. The diffuse reflections are used to estimate photometric parameters of the illuminants. We also notice that common source types are degenerate cases of the general source model under certain conditions. Therefore, we can approximate light sources with common source types by checking the conditions. The approximations serve as type determinations of light sources, which makes our framework extremely useful for lighting related algorithms which need prior knowledge about light sources. Experiment results on a variety of real images demonstrate the efficiency and accuracy of our algorithm.

Spectral design considerations for white LED color rendering

White LED spectra for general lighting should be designed for high luminous efficacy as well as good color rendering. Multichip and phosphor-type white LED models were analyzed by simulation of their color characteristics and luminous efficacy of radiation, compared with those of conventional light sources for general lighting. Color rendering characteristics were evaluated based on the CIE Color Rendering Index CRI, examining not only Ra but also the special color rendering indices Ri, as well as on the CIELAB color difference Eab for the 14 color samples defined in CIE 13.3. Several models of three-chip and four-chip white LEDs as well as phosphor-type LEDs are optimized for various parameters, and some guidance is given for designing these white LEDs. The simulation analysis also demonstrated several problems with the current CRI, and the need for improvements is discussed. © 2005