LED-based Lighting Research Articles

Combinatorial screening of luminescent and structural properties in a Ce(3+)-doped Ln-Al-Si-O-N (Ln = Y, La, Gd, Lu) system: the discovery of a novel Gd3Al(3+x)Si(3-x)O(12+x)N(2-x):Ce(3+) phosphor.

The discovery of novel phosphors for use in light emitting diodes (LED) has gained in significance because LED-based solid-state lighting applications now attract a great deal of attention for energy savings and environmental concerns. Recent research trends have centered on the discovery of novel phosphors, not on slight variations of well-known phosphors. In a real sense, novelty goes beyond simple variations or improvements in existing phosphors. A brilliant strategy for the discovery of novel phosphors is to introduce an appropriate activator to existing inorganic compounds. These compounds have structures that are well-defined in crystallographic structure databases, but they have never been considered as a phosphor host. Another strategy is to discover new host compounds with structures that cannot be found in existing databases. We have simultaneously pursued both strategies by employing metaheuristics-assisted combinatorial material search techniques. In the present investigation, we screened a search space consisting of Ln-Al-Si-O-N (Ln = Y, La, Gd, Lu), and thereby we discovered a blue-light-emitting novel phosphor, Gd3Al(3+x)Si(3-x)O(12+x)N(2-x):Ce(3+), with a monoclinic system in the C2 space group--a potential candidate for UV-LED applications.

Polymeric Materials in Phosphor-Converted LEDs for Lighting Applications: Outlook and Challenges

Solid-state lighting technologies such as LED-based lighting are steadily gaining market share and promise significant energy efficiencies. This article describes some key polymer materials used in LED packages, especially for phosphor encapsulation. We discuss the use of various silicone materials as encapsulants, and bring out the advantages and issues with this approach. The key issues discussed include thermal stability, the consequences of exposure to high temperatures such as discoloration and mechanical failure, refractive index matching, and heat removal (thermal conductivity). We present a number of approaches designed to alleviate these issues, including the use of composite/hybrid materials.

Sliding-Mode-Control-Based Boost Converter for High-Voltage–Low-Power Applications

This paper presents the analysis and design of a very high-voltage-gain single-stage boost converter operating at the boundary between continuous conduction mode (CCM) and discontinuous conduction mode (DCM). The converter is supplied by a 12-V car battery and attains 1200 V with a voltage gain of 100. The use of a hysteretic comparator in the control loop precludes the risk of modulator saturation and facilitates the operation at the mentioned boundary. Sliding-mode control theory is applied to analyze the dynamic behavior of the switching regulator and to establish the system stability conditions. The performance of the converter is investigated using silicon carbide (SiC) devices for the power switch realization. LED-based efficient lighting systems can be a promising application of the proposed system.

The Impact of Light Emitting Diodes

The Electrochemical Society Interface • Winter 2015 • www.electrochem.org 43 T he Luminescence and Display Materials Division (LDM) was last featured in Interface in the winter 2009 issue. In that issue I wrote about the emerging technology of solid state lighting (SSL), which was then the subject of intensive research by many members of LDM. At that time, one envisioned the replacement of inefficient incandescent lamps by LED-based systems, leading to more than 3% reduction of energy consumption in the U.S., and accompanied by a similar reduction in pollution, greenhouse gases, and costs.1 It turns out that our predictions have been surpassed by recent developments in solid state lighting: the combined efforts of industry and academia, in conjunction with government support, have led to LED-based lighting devices, which are not only superior to incandescent lamp, but also to fluorescent lighting, the main light source in commercial and industrial applications. While high quality fluorescent lamps yield about 100 lumens/watt, hereby reaching the achievable potential for this technology, SSL devices have reached higher efficiencies already, with prototypes reaching 200 lumens/ watt.2 The importance of these rapid, and globally important, developments was recognized in 2014 by the Nobel Prize Committee, which awarded the Nobel Prize in Physics 2014 to Isamu Akasaki, Hiroshi Amano, and Shuji Nakamura, “for the invention of efficient blue light-emitting diodes which has enabled bright and energysaving white light sources.”3 In this issue, Martin Hermus and Jakoah Brgoch report on recent approaches to develop efficient and stable phosphor materials in their article, “Phosphor by Design: Approaches Toward the Development of Advanced Luminescent Materials.” One would expect phosphor development to be an important research topic, but other aspects of SSL attract attention as well. The contribution “Polymeric Materials in Phosphor-Converted LEDs for Lighting Applications: Outlook and Challenges,” by Maxim Tchoul, Alan Piquette, and Alexander Linkov, addresses in detail the role of polymeric materials in solid state lighting, New technologies often have negative, unforeseen implications, and the article “Impact of Light Emitting Diode Adoption on Rare Element Use in Lighting: Implications for Yttrium, Europium, and Terbium Demand,” by Anthony Y. Ku, Anant A. Setlur, and Johnathan Loudis, addresses the question of possible shortages of critical rare earth elements. While the articles in this issue emphasize SSL, it should be noted that our LDM Division does (and should) provide a forum for all aspects of light-emitting processes and techniques for their implementation, and I find that advances in the different research areas often profit from the intellectual cross-fertilization among our members at the ECS meetings. Thus I hope to see you at PRiME 2016 in Honolulu.

A green-emitting α-substituted β-diketonate Tb3+ phosphor for ultraviolet LED-based solid-state lighting

The α-substituted β-diketonate [Ln(3Cl-acac)3(H2O)2] [Ln = Tb, Gd] complexes (with 3Cl-acac– being 3-chloro-2,4-pentanedionate) were characterized by elemental analysis, infrared, ultraviolet (UV)-visible and photoluminescence spectroscopies. For comparison purposes regarding photoluminescence, the well-known [Tb(acac)3(H2O)2] complex was also synthesized. By considering the phosphorescence spectra of [Gd(3Cl-acac)3(H2O)2], the effect of chloride replacement of hydrogen on the triplet state energy of the 3Cl-acac ligand was revealed. To support the interpretation and rationalization of the experimental results, Time-dependent DFT calculations were performed on Tb(3Cl-acac)3(H2O)2. Additionally, the possibility of Tb(3Cl-acac)3(H2O)2 to be used as potential green-emitting phosphor material for solid-sate light emitting diodes was evaluated. A prototype was successfully fabricated coating a near-UV LED (370 nm) with the Tb(3Cl-acac)3(H2O)2 complex.

Experimental assessment of color-rendering indices and color appearance under varying setups

The Color-Rendering Index (CRI) for light source is a quantitative measure of the capability to preserve color appearance of illuminated objects. Recently, CRI has had a renewed interest because of the new LED-based lighting systems. These sources usually have a Color-Rendering Index rather low, but a good preservation of color appearance and a pleasant visual appeal. Various attempts to develop a more reliable new color-rendering index have been done so far, but researchers are still working on the topic. This article presents the open issues related to CRI and discusses some of the approaches available in literature. In order to have a baseline to verify the above points, we present an experiment performed with human observers to assess the appearance preservation of a color under a set of light sources. The test protocol uses 3D reference objects and can be used as an alternative way to assess CRI. The results are then compared with a range of available color rendering indices. The goal is not to make a rank among CRIs, rather to assess their variability relative to human judgment through different setups and light sources.

High-performance lighting evaluated by photobiological parameters.

The human reception of light includes image-forming and non-image-forming effects which are triggered by spectral distribution and intensity of light. Ideal lighting is similar to daylight, which could be evaluated by spectral or chromaticity match. LED-based and CFL-based lighting were analyzed here, proposed according to spectral and chromaticity match, respectively. The photobiological effects were expressed by effectiveness for blue light hazard, cirtopic activity, and photopic vision. Good spectral match provides light with more similar effects to those obtained by the chromaticity match. The new parameters are useful for better evaluation of complex human responses caused by lighting.

A smart LED luminaire for energy savings in pedestrian road lighting

In this paper, an energy efficient streetlight for pedestrian roads is introduced. Energy efficiency is achieved via up-to-date light-emitting diode (LED) technology and added intelligence utilising integrated sensors and wireless control. Thermal and electrical design of the luminaire contributed to good technical functionality. The performance of the luminaire was validated with testing. The luminaire was compared with commercial lamp and LED-based street lighting technology by technical values and user acceptance. Energy savings of 19–44% through improved luminous efficacy was demonstrated without added intelligence. With smart control further power saving potential of 40–60% was shown depending on the lighting environment and pedestrian presence. User feedback of a pilot installation comparing commercial luminaires with the newly developed streetlight revealed that on average the users preferred the developed streetlight over the commercial luminaires.

Thermal simulation and validation of LED-based luminaires using two-resistor compact thermal model

The increase in the LED junction temperature is an important problem since it directly affects the lumen output and the colour characteristics of the LED chips, resulting in low performance in LED-based lighting systems. In this study, commercial computational fluid dynamics software is used with the JEDEC’s two-resistor compact thermal model to analyse the temperature distribution in two selected luminaires. It is aimed to show that use of the two-resistor model and measurement combination is a fast and easy way of predicting thermal behaviour of the system and LED junction temperatures instead of trial and error designs and thus ensures a better estimation for the total luminous flux of the luminaire and lowers the costs and time required for the prototyping processes.

Toward a “Standard” Television Camera Color Model

The introduction of high-efficiency light sources such as LEDs in TV and film production studios has revitalized the earlier work of W. N. Sproson, and E. W. Taylor (BBC) on the effects of lighting for television. In the report of this work at IBC2011, Alan Roberts gave a well-informed look into what may well be the consequences of uncritically introducing LED-based studio lighting into program production. In order to fully realize the proposed Television Lighting Consistency Index (TLCI-2012), it is necessary to have information about the spectral sensitivity in modern TV cameras using CCD and CMOS sensors. Since camera manufacturers are reluctant to disclose such information, work has been undertaken at the Norwegian Broadcasting Corp. (NRK) to measure the spectral sensitivity properties of modern HDTV cameras. The result of this work has enabled the authors to develop the proposal for a “standard” television camera color model that is presented in this paper.

LED 기반 그린에너지 조명시스템을 위한 전력품질 측정

LED 기반 그린에너지 조명 시스템의 성공적인 연구 개발과 원만한 설치 운영을 위해서는 펄스 파, 스파이크 파를 비롯한 비선형신호와 고조파, sag, swell 등을 포함한 불요신호에 대한 실시간 전력품질측정이 요구된다. 본 논문에서는 그린에너지 조명시스템 응용을 타깃으로 기존 저주파수 대 (60Hz～수KHz)는 물론 수십 KHz 이상의 고주파수 대에 발생하는 각종 전원 신호 분석이 가능한 저가형 전력품질측정 (power quality measurement: PQM) 방안을 제안하고, 이를 TI 320F28335 MCU(micro-controller unit) 기반 PQM 테스트 베드로 구현한다. 제안된 알고리즘은 CCS (Code Composer Studio) 3.3 환경에서 C언어로 작성하였으며, 임의 신호 발생기(NF-WF1974)로부터 발생된 모의 신호를 활용하여 구현된 알고리즘을 검증한다. 테스트 베드를 이용하여 LED SMPS로부터 발생되는 각종 비선형 전류 신호 측정, FFT를 이용한 고조파 신호의 분석이 가능할 뿐 아니라 이산 웨이블렛 변환을 이용한 sag, swell, interruption 등의 고품질 전력신호 측정도 가능하다.

A transportable system for the in situ recording of color Denisyuk holograms of Greek cultural heritage artifacts in silver halide panchromatic emulsions and an optimized illuminating device for the finished holograms

In this paper we will present the Z-Lab transportable color holography system, the HoLoFoS illuminator and results of actual in situ recording of color Denisyuk holograms of artifacts on panchromatic silver halide emulsions. Z-lab and HoLoFoS were developed to meet identified prerequisites of holographic recording of artifacts: a) in situ recording b) a high degree of detail and color reproduction c) a low degree of image distortions. The Z-Lab consists of the Z3RGB camera, its accessories and a mobile darkroom. HoLoFoS is an RGB LED-based lighting device for the display of color holograms. The device is capable of digitally controlled intensity mixing and provides a beam of uniform color cross section. The small footprint and emission characteristics of the device LEDs result in a narrow band, quasi point source at selected wavelengths. A case study in recording and displaying ‘Optical Clones’ of Greek cultural heritage artifacts with the aforementioned systems will also be presented.

Optimum design domain of LED-based solid state lighting considering cost, energy consumption and reliability

Design parameters of LED-based solid state lighting products are interdependent and the corresponding requirements are dictated by operating conditions. We propose a scheme to define optimum design domains of LED-based luminaires for a given light output requirement by taking cost, energy consumption and reliability into consideration. First three required data sets to define design domains are expressed as contour maps in terms of the forward current and the junction temperature (If and Tj): (1) face lumen and cost requirement as lumen/LED; (2) power consumption and energy requirement as luminaire efficacy (LE); and (3) reliability requirement as L70 lifetime. Then, the available domain of design solutions is defined as a common area that satisfies all the requirements of a luminaire. The proposed scheme is implemented for a wall wash light and the optimum design solutions are presented.

LED기반 실내 조명 구조에 따른 무선통신 채널의 품질 분석

가시광 통신은 반도체 LED를 이용하여 정보를 브로드캐스트 하며, 백색광 LED는 조명과 광무선 통신을 하나의 광원을 사용하여 제공할 수 있다. 본 논문에서는 단일칩 백색광 LED를 활용하여 조명과 통신에 적합한 조명기구를 제안한다. 백생광 LED 조명기구의 구조에 따른 수평 조도특성, 무선채널 대역특성, 심볼간 간섭현상, 신호대 잡음비 및 비트 에러율을 분석함으로써 장애물이 있는 경우 제안한 LED 조명이 기존의 조명보다 우수한 조명 및 통신 채널을 제공함을 보이고자 한다. Visible light communications (VLC) uses modern solid-state LEDs to broadcast information. Emerging white-light LEDs allows the combination of lighting and optical wireless communication in one optical source. In this paper, a new LED lighting using one-chip-type white LED is proposed for efficient illumination and optical wireless communications. Performance analysis such as horizontal illuminance, 3-dB cut-off frequency, inter-symbol interference, signal-to-noise ratio and bit-error rate shows the effects of the shapes of LED lighting. Performance of the proposed LED lighting under the existence of obstacles is superior to that of the existing LED lighting in illumination and optical wireless communication.

A terracotta bio-battery

Terracotta pots were converted into simple, single chamber, air-cathode bio-batteries. This bio-battery design used a graphite-felt anode and a conductive graphite coating without added catalyst on the exterior as a cathode. Bacteria enriched from river sediment served as the anode catalyst. These batteries gave an average OCV of 0.56V±0.02, a Coulombic efficiency of 21±5%, and a peak power of 1.06mW±0.01(33.13mW/m2). Stable current was also produced when the batteries were operated with hay extract in salt solution. The bacterial community on the anode of the batteries was tested for air tolerance and desiccation resistance over a period ranging from 2days to 2weeks. The results showed that the anode community could survive complete drying of the electrolyte for several days. These data support the further development of this technology as a potential power source for LED-based lighting in off-grid, rural communities.

Combustion synthesis of multicomponent ceramic phosphors for solid state lighting

About 50% of the world’s need for lighting is provided by artificial lighting. For over the last decade, the world has witnessed rapid shift from conventional Hg-based lighting to LED-based solid state lighting (SSL). SSL technology extensively uses YAG:Ce3+ phosphor for production of white light emitting devices (LEDs). Part of the blue light from the (In,Ga)N LED chip is absorbed by a thin layer of Ce3+-doped YAG and is converted into yellow light. The combination of blue and yellow gives a bright white light source with an overall energy efficiency exceeding that of a compact fluorescent lamp. Several soft chemical routes have been explored for synthesis of YAG but were discarded due to their complex nature, high cost for the industrialization, phase impure materials, etc. In this paper we describe rapid one-step modified combustion synthesis of YAG:Ce3+ and related phosphors carried out at 500°C using a mixed fuel. Photoluminescence spectra of YAG:Ce3+ and LED prepared thereof are comparable with those of commercial phosphors.

Design of a Soft-Switching Asymmetrical Half-Bridge Converter as Second Stage of an LED Driver for Street Lighting Application

High-brightness LEDs are considered remarkable lighting devices due to their high reliability, chromatic variety, and increasing efficiency. As a result, a high number of solutions for supplying LED strings are emerging. One-stage solutions are cost-effective, but their efficiency is low because they have to fulfill several purposes with only one converter: power factor correction (PFC), galvanic isolation (in some cases), and current regulation. Two-stage and three-stage solutions have higher efficiency because each stage is optimized for only one or two tasks and they are the preferred options when supplying several strings at the same time. In this paper, a two-stage solution is proposed. The first stage is the well-known PFC boost converter. The second stage, on which this paper is focused, is the asymmetrical half bridge (AHB). Its design has been optimized based on the needs and characteristics of LED-based street lighting applications. The proposed transformer design (with asymmetrical secondary windings) minimizes the conduction losses while the model of the converter during the dead times optimizes their duration, reducing switching losses in the MOSFETs and diodes. Experimental results obtained with a 40-W prototype show an efficiency as high as 94.5% for this second stage and validate the proposed design procedure and model.

Electrical Through-Hole and Planar Interconnect Generation in Roll-to-Roll LED Lighting Manufacturing using Industrial Inkjet Printheads

ABSTRACTDespite the availability of many high-volume and low-cost manufacturing processes for LED-based lighting applications, relying mainly on fixed patterns such as LED-backlights and RGB-pixelated displays, novel applications, such as “mood lighting” or interior wall displays call for more complicated and shaped LED arrangements. The presented work is based of a novel roll-to-roll (R2R) process to adaptively and cost-efficiently generate LED arrangements on RMPD® substrates.Inkjet printing of planar and though-hole electrical interconnections is of high importance to the process, as it provides a fully digital way of interconnecting devices electrically, accounting for the actual position of the component and spatially provide different ink film thicknesses.Xaar’s industrial inkjet printheads are used to dispense defined volumes of 50 pL of a silver nanoparticle ink in order to provide high reliability and good positioning accuracy while main-taining low satellite drop densities. Specific printing strategies are investigated at a print speed of 0.1 m/s to allow for a reliable electrical connection in case of up to 50 μm deep via connections to the buried component.Due to the low glass-transition nature of the underlying substrates, low sintering tempera-tures are required to preserve the mechanical properties of the substrate. Low temperature oven sintering yielding sufficient conductivity to drive a current of 40 mA will be discussed.

Phosphors for LED-based Solid-State Lighting

The efficacy of solid-state lighting (SSL) based upon InGaN LEDs has improved by >10x over the past decade: the efficacy of cool white LEDs surpasses linear fluorescent lamp (LFLs) efficacies (>100 lm/W) and warm white 1W LEDs surpasses compact fluorescent lamps (CFLs) efficacies (>60-70 lm/W).

LEDs for Solid-State Lighting: Performance Challenges and Recent Advances

Over the past decade, advances in LEDs have enabled the potential for wide-scale replacement of traditional lighting with solid-state light sources. If LED performance targets are realized, solid-state lighting will provide significant energy savings, important environmental benefits, and dramatically new ways to utilize and control light. In this paper, we review LED performance targets that are needed to achieve these benefits and highlight some of the remaining technical challenges. We describe recent advances in LED materials and novel device concepts that show promise for realizing the full potential of LED-based white lighting.