We present an empirical model of LED emission spectra that is applicable to both InGaN and AlInGaP high-flux LEDs, and which accurately predicts their relative spectral power distributions over a wide range of LED junction temperatures. We further demonstrate with laboratory measurements that changes in LED spectral power distribution with temperature can be accurately predicted with first- or second-order equations. This provides the basis for a real-time colorimetric feedback system for RGB LED clusters that can maintain the chromaticity of white light at constant intensity to within ±0.003 Δuv over a range of 45 degrees Celsius, and to within 0.01 Δuv when dimmed over an intensity range of 10:1.

GaN vertical LED on metal alloy substrate (VLEDMS) has been successfully realized for wavelength spectrum from near UV to green color. Owing to the vertical structure and highly heat-conductive metal alloy substrate, VLEDMS exhibits an ultra high brightness and excellent reliability suitable for solid state lighting (SSL) application. A brightness of 80Lm/W using 450 nm chip mixed with yellow phosphor was achieved by optimization of LED structure epitaxy, chip process and packaging. Using 405 nm chip with polychromatic phosphor a 50 Lm/W white light with color rendering index better than 90 was obtained. We also can get very good uniform correlated color temperature from package with VLEDMS chip.

In this paper we describe GaN based Vertical Light Emitting diode on Metal Alloy Substrate (VLEDMS) as a disruptive technology to solve the heat dissipation and current-crowding effect for the power device operated at high current. We focus on reliability features of VLEDMS under various operation regimes required for solid state lighting (SSL) application.

The transport and annealing properties of phosphorus-doped (Zn,Mg)O thin films grown via pulsed laser deposition (PLD) are studied. The electron carrier concentration for (Zn,Mg)O:P films decreases with increasing deposition and Ar annealing temperature. All the films exhibit good crystallinity with c-axis orientation. This result indicates the importance of activation of the P dopant in (Zn,Mg)O:P films. The as-deposited ZnO:P film properties show less dependence on the deposition growth temperatures. The resistivity of the (Zn,Mg)O:P films is significantly higher than the ZnO:P films grown under similar conditions, indicating separation of the conduction band edge relative to the defect donor state. The annealed ZnO:P films are n-type with resistivity dependent on annealing temperature.

Recently, there has been great interest in developing direct white-light phosphors for solid state lighting. Current commercial white light emitting diodes (LEDs) rely on complicated fabrication methods to produce white light. Utilizing magic-sized, white-light emitting cadmium selenide (CdSe) nanocrystals as a direct white-light phosphor eliminates the need for complex doping schemes and deposition techniques. Herein we report preliminary data representing the first elementary steps in designing and optimizing device architectures for building high-quality, highly efficient white-light emitting LEDs for solid state lighting.

InGaN/GaN multiple quantum well (MQW) light emitting diode (LED) structures with blue and green light emissions have been grown on sapphire substrates by metalorganic chemical vapor deposition. They are investigated by high-resolution X-ray diffraction (HR-XRD), high-resolution transmission electron microscopy (HR-TEM), photoluminescence (PL) and photoluminescence excitation (PLE). HR-XRD showed multiple satellite peaks up to 10th order due to the quantum well superlattice confinement effects. HR-TEM determined the MQW structures and parameters, indicating the high quality of layer interfaces of these LED samples. Excitation power-dependent PL predicates that both piezoelectric field-induced quantum-confined Stark effect and band filling effect influence the luminescent properties. Temperature-dependent PL shows that the QW PL emission peak exhibits a monotonic red-shift and that the full width at half maximum of the PL band shows a W-shaped temperature-dependent behavior with increasing temperature. From the PLE results, a large energy difference, so-called quantum confined Stokes shift, between the band-edge absorption and emission was observed. Penetrating TEM revealed the V-shape defects, and quantum dot-like structures within the InGaN well region, which leads to intense light emissions from these MQW LEDs.

Coupling of a InGaN/GaN multi-quantum well (MQW) and semitransparent metal layer is shown to result in dramatic enhancement of spontaneous emission rate by the surface plasmon effect in the optical spectral range. A five-pairs 18.5nm InGaN/GaN MQW is positioned 175nm, form various thickness (t=5~50nm) silver layer. And periodic patterns (p=0.25~0.8μm) are defined in the top semitransparent metal layer by e-beam lithography, which are grating structures can be incorporated into the metal film to excite surface plasmon between the interference of the metal film and semiconductor. We have experimentally measured photoluminescence intensity and peak position of spontaneous emission of the fabricated structures and compared with the unprocessed samples, whilst still ensuring that most of the emission takes place into the surface plasmon (SP) mode. And the implication of these results for extracting light by reducing total internal reflection (TIR) from light emission diode is discussed.

Silicone based materials have attracted considerable attention from light emitting diode (LED) manufacturers for use as encapsulants and lenses for many high brightness LED (HB LED) devices. Currently silicones function in two key roles in HB LED devices, (1) as protective lenses and (2) stress relieving encapsulants for wire bond protection. The key attributes of silicones that make them attractive as light path materials for high brightness HB LEDs include their high transparency in the UV-visible region, controlled refractive index (RI), stable thermo-mechanical properties, and tuneable modulus from soft gels to hard resins. This paper will describe recent developments in moldable silicone hard resin materials. Progress on cavity moldable and liquid injection moldable (LIM) silicone compositions for discreet components is described. Also, an example of liquid injection overmolding is presented.

White light-emitting-diodes (LEDs) are known as a new generation lighting source. Using a blue LED with a phosphor layer which is excited by blue light and down-converting to the second light, such as yellow light, white light can be produced. Using a one-dimensional mathematical model, we can describe the light propagation by simple absorption, conversion, and reflection terms. We use a multiple phosphor film coating method to determine the coefficient of the model, followed by analysis to determine the optimum phosphor layer LED package. With a phosphor layer plus a yellow light reflector, the white light extraction efficiency could be above 0.9 relative the conventional package's 0.6- 0.8.

At present, light-emitting diode (LED) modules in various shapes are developed and designed for the general lighting, advertisement, emergency lighting, design and architectural markets. To compete with and to surpass the performance of traditional lighting systems, enhancement of Lumen output and the white light quality as well as the thermal management and the luminary integration are key factors for success. Regarding these issues, white LEDs based on the chip-on-board (COB) technology show pronounced advantages. State-of-the-art LEDs exploiting this technology are now ready to enter the general lighting segments. We introduce and discuss the specific properties of the Tridonic COB technology dedicated for general lighting. This technology, in combination with a comprehensive set of tools to improve and to enhance the Lumen output and the white light quality, including optical simulation, is the scaffolding for the application of white LEDs in emerging areas, for which an outlook will be given.

Dimming is an important and necessary feature for light sources used in general lighting applications. An experimental study was conducted to quantify the spectral and luminous efficacy change of high-power colored and pc-white LEDs under continuous current reduction (CCR) and pulse-width modulation (PWM) dimming schemes. For InGaN-based blue, green, and pc-white LEDs, the peak wavelength shifts were in opposite directions for the two dimming schemes. The peak wavelength showed a blue shift with increased current, most likely due to band filling and QCSE dominated effects. InGaN LEDs exhibited red shifts with increased duty cycle, which is dominated by junction heat. AlInGaP red LEDs show mainly thermal-induced red shift with increased current or duty cycle. In addition, the luminous efficacy was always higher for the CCR dimming scheme at dimmed levels, irrespective of the LED type. Keywords: Light-emitting diodes (LEDs), white LEDs, mixed-color white LEDs, pulse-width modulation (PWM), continuous current reduction (CCR), peak wavelength shift, luminous efficacy

The performance of white pc LEDs based on violet chips is analyzed in terms of several metrics (lm/W, mW/lm, and package efficiency). A calculation is developed to evaluate package efficiency using spectroradiometric measurements and accounting for extraneous factors (Stokes' loss, luminous efficacy of the phosphor and bleed). The method is demonstrated on a state of the art "warm white" power LED, and performance entitlement is also discussed.

The successful commercialization of solid-state lighting for general illumination will require an effective method to characterize the color quality of these sources. The distinctive spectral characteristics of solid-state lighting sources present both unique challenges and opportunities with regards to color quality. Color quality is difficult to define, much less measure. Several aspects of color quality, including color fidelity (rendering), chromatic discrimination, and general population preferences must be considered. In some instances, these factors are contradictory. For example, observers tend to prefer lamps that increase object color chroma (vividness), though such chroma increases are deviations from color fidelity. In addition to devising a way to balance the influence of these different dimensions of color quality, consideration must be given to ways of communicating color quality in a simple way, which permits comparison between products. At NIST we're approaching this problem by developing a computational method that takes inspiration from the Color Rendering Index (CRI), but incorporates other aspects of color quality. The output of this Color Quality Scale (CQS) is a composite score incorporating a lamp's ability to accurately render object colors, permit precise discrimination between different colors, and display object colors in a way that is visually pleasing to typical consumers. Visual experimentation will be vital to improve and validate this method, which was initially developed with colorimetric simulations. Preliminary experimentation has begun, focusing on the issues most relevant to the development of commercial standards for color quality.

Due to their small dimensions when used for visible light, the patterning of photonic crystals has only been possible with costly electron beam lithography and low throughput R&D and pilot production grade imprint lithography. This paper will focus on results from a high throughput imprint tool capable of processing over 20 wafers per hour on 50- 100mm sapphire, GaAs, SiC, Ge and metal substrates. An overview of the process used as well as the results of patterning photonic crystal patterns on sapphire wafers and etching them into a SiO2 hard mask will be presented. Finally an analysis of the cost of ownership which currently stands at ~ $20/wf (<$0.01/mm² for 50mm wafers) will be presented and opportunities for improvement discussed.

The purpose of this study is to develop procedures for evaluating the transient effects of solid state light sources used as illumination sources at night. Traditional light sources used at night are designed to preserve dark adaptation by employing long wavelength visible sources that minimally affect rod photoreceptor sensitivity, while new LED light sources provide a mix of visible spectral sources with visible spectral components that may effect rod function and possibly impede night vision. The Crawford transformation was used generate spectral dark adaptation functions for LED flashlight background effects on dark adaptation induced by background exposure conditions from four solid state light sources. Increment background spectral sensitivity functions were generated for each of four LED flashlight sources (S1, S2, & S3) as well as from a merger of each LED source with a broadband Goldman-Weekers (GW) dark adaptometer source (S5) to simulate transition for day to night light environments. Increment background spectral sensitivity for both methods of generating increment spectral sensitivity were consistent in showing similar spectral background effects on spectral sensitivity but differed in the dynamic range of recovery. Those spectra that had components in the middle wavelength region (S2 and S3) showed a more restricted rod function as compared with S1 and S2.

A new trend in illumination is to use dynamic light to set or dynamically vary the ambience of a room or office. For this we need color tunable spots that can reliably vary over at least a wide range of color temperatures, and preferably also more saturated colors. LEDs are in principle ideally suited for this application thanks to their nature of emitting light in a relatively narrow band. For color tunable spot lighting based on the concept of mixing RGB LED colors, the key results have been presented before. Limitations of these 3-intrinsic-color mixing systems with high color rendering properties are found in a limited operating temperature range due to wavelength shifts, a limited color temperature range, and a low maximum operating temperature due to a strong flux decrease with increasing temperature. To overcome these limitations, a 3-color R_pcGB system with phosphor-converted red (R_pc) and a 4-color RAGB system have been investigated. With both systems, a CRI of at least 80 can be maintained over the relevant color temperature range of approximately 2700 K to 6500 K. In this paper we compare these concepts on overall system aspects and report on the performance of prototype spot lamps. The main features of the RAGB and R_pcGB spot lamp concepts can be summarized as: 1) The RAGB spot overcomes CRI and gamut shortcomings of RGB light sources and gives much freedom in wavelength selection, but suffers from temperature sensitivity and complex controls; 2) The R_pcGB spot overcomes shortcomings concerning CRI and thermal dependence of RGB sources and enables relatively simple controls, but needs an improved overall red efficacy. With both color concepts, prototype spot lamps have been built. The amber to red emitting nitridosilicate-based phosphors can be wavelength-tuned for optimal performance, which is found at a peak emission around 610 nm for high color quality systems. This results in a simple and very robust system with good color consistency. For the RAGB system, a spot lamp has been developed, consisting of a 4-chip light source, an optical system with mixing rod that provides color homogenization and beam shaping, and an electronic drive and control unit based on temperature feed forward. Flux- and color-rendering performance can be tuned according to the application requirements.

This paper presents an experimental analysis of high brightness light emitting diodes (HBLEDs) performance and stability under dc and pulsed current bias. Three different families of HBLEDs from three leading manufacturers have been considered. The analysis was carried out by means of current-voltage, integrated optical power and electroluminescence measurements, and failure analysis. After an initial characterization of the electrical, optical and thermal behavior of the devices, a set of ageing tests was carried out, both under dc and pulsed bias conditions. Identified degradation modes were efficiency decrease, series resistance increase, leakage current increase, and modifications of the emitted spectrum. Characterization of devices behavior during stress indicated (i) generation of non-radiative components, (ii) degradation of the anode contacts and bonding wires, (iii) degradation of the phosphorous layer conversion efficiency and (iv) of the plastic package as possible responsible of the electrical and optical degradation of the LEDs. Comparison between dc and pulsed stress carried out using the same average current level and different duty cycle values showed that the use of pulsed bias can reduce the degradation rate with respect to dc bias. However, for duty cycles lower than 20%, fast degradation and abrupt ruptures can take place, due to the high peak current levels.

Recently, many studies have used optical ray-tracing analysis to investigate novel concepts of phosphor-converted white LEDs. Even though optical ray-tracing is a convenient tool, the accuracy of the results depends very much on the optical properties of the various components within the package used in the analysis. Presently, light transmission, reflection, and absorption properties of white LED phosphors are not very well quantified. Therefore, a laboratory study was conducted to quantify at different wavelengths of light the optical properties of a medium that has YAG:Ce phosphor mixed into epoxy. When short-wavelength radiation (blue light) strikes the epoxy-phosphor medium, some portion of the blue light is converted to longer wavelength radiation (yellow light). At a phosphor density suitable for creating a balanced white light, the amount of back-transferred and forward-transferred light, including blue and yellow light, are 53% and 47%, respectively. At a similar phosphor density, when green and red radiant energies strike the epoxyphosphor medium, most of the energy is not converted by the YAG:Ce phosphor because it is beyond the phosphor's excitation region. In this case, nearly equal amounts of green and red radiant energy are transferred in the backward and forward directions. To demonstrate the usefulness of the results obtained in this study, an optical ray-tracing analysis of a remote phosphor white LED package was conducted. This analysis showed that the surface finish of the reflector cup of a reflective type remote phosphor white LED package does not affect extraction efficiency.

Thermal transient measurements of high power GaN-based LEDs with multi-chip designs are presented and discussed in the paper. Once transient cooling curve was obtained, the structure function theory was applied to determine the thermal resistance of packages. The total thermal resistance from junction to ambient considering optical power is 19.87 K/W, 10.78 K/W, 6.77 K/W for the one-chip, two-chip and four-chip packages, respectively. The contribution of each component to the total thermal resistance of the package can be determined from the cumulative structure function and differential structure function. The total thermal resistance of multi-chip packages is found to decrease with the number of chips due to parallel heat dissipation. However, the effect of the number of chips on thermal resistance of package strongly depends on the ratio of partial thermal resistance of chip and that of slug. Therefore, an important thermal design rule for packaging of high power multi-chip LEDs has been analogized.

Heat at the junction of light-emitting diodes (LED) affects the overall performance of the LED in terms of light output, spectrum, and life. Usually it is difficult to measure junction temperature of a LED directly. There are several techniques for estimating LED junction temperature. One-dimensional heat transfer analysis is one of the most popular methods for estimating the junction temperature. However, this method requires accurate knowledge of the thermal resistance coefficient from the junction to the board or pin. An experimental study was conducted to investigate what factors affected the thermal resistance coefficient from the junction to the board of high-power LED. Results showed that the thermal resistance coefficient changed as a function of ambient temperature, power dissipation at the junction, the amount of heat sink attached to the LED, and the orientation of the LED with the heat sink. This creates a challenge for using onedimensional heat transfer analysis to estimate junction temperature of LEDs once incorporated into a lighting system. However, it was observed that junction temperature and board temperature maintains a linear relationship if the power dissipation at the junction is held constant.

We introduce an alternative to pulse width modulation (PWM) for LED intensity control called "Extended Parallel Pulse Code Modulation." Whereas PWM typically requires a microcontroller with a dedicated hardware PWM controller for each channel, we can easily implement pulse code modulation (PCM) in firmware. We show that the spectral content of PWM and PCM signals is equivalent, and so there is no disadvantage from an EMI perspective for circuit or cabling design. We next introduce a PCM-based algorithm that enables a single microcontroller to drive up to one hundred LED channels in real-time with 8- to 12-bit resolution. This parallel PCM technique is suitable, for example, for LED backlighting of video displays and LED-based theatrical lighting systems. Depending on the application, we can implement the algorithm in firmware or in hardware with a field-programmable gate array. A modification of the algorithm takes advantage of the characteristics of the Ferry-Porter law for visual flicker to reduce the modulation frequency. This extended parallel PCM technique relies on the principle of temporal dithering (adapted from digital audio techniques) to reduce quantization errors in the LED intensity signals.

Ray tracing simulations of LED lighting systems typically use the smooth angular intensity profiles supplied by the LED manufacturer. However, measurements of a range of 5 mm LEDs presented in this paper show bright regions in the LEDs' angular distributions. The intensity patterns and bright regions vary between different LEDs, even when the measured angle for 50% integrated light output (as measured using an integrating sphere) is similar. When non-diffuse or partially diffuse optical elements such as clear light guides are part of a lighting system design, this source profile unevenness is intensified, so that bright caustic rings are formed. We have performed lighting simulations using coloured LEDs coupled into a clear light guide, and compared the light output using smoothed LED profiles with that using actual measured profiles. The simulated light patterns projected from the end of a light guide onto a screen are compared with that obtained by experiment. It is shown that the uniqueness of individual LED beam patterns needs to be taken into account for simulation accuracy. This is particularly important when the lighting system combines the output from several LEDs. It is also shown to be crucial in optimising the amount and type of diffusion required for homogenising the light distribution.

In this work, ZnO has been investigated as a substrate technology for GaN-based devices due to its close lattice match, stacking order match, and similar thermal expansion coefficient. Since MOCVD is the dominant growth technology for GaN-based materials and devices, there is a need to more fully explore this technique for ZnO substrates. Our aim is to grow low defect density GaN for efficient phosphor free white emitters. However, there are a number of issues that need to be addressed for the MOCVD growth of GaN on ZnO. The thermal stability of the ZnO substrate, out-diffusion of Zn from the ZnO into the GaN, and H₂ back etching into the substrate can cause growth of poor quality GaN. Cracks and pinholes were seen in the epilayers, leading to the epi-layer peeling off in some instances. These issues were addressed by the use of H₂ free growth and multiple buffer layers to remove the cracking and reduce the pinholes allowing for a high quality GaN growth on ZnO substrate.

Intense visible blue to red emissions were obtained from SiN_x thin films prepared by plasma enhanced chemical vapor deposition (PECVD) using SiH₄ and NH₃ as the source gases. A continuous blue shift of the photoluminescence (PL) peak from 660nm to 440nm was observed by increasing the NH₃ flow rate from 20 to 150sccm, while the flow rate of N₂ diluted 2% SiH₄ was fixed at 650sccm. This controllable PL was attributed to the quantum confinement effect of Si quantum dots (QDs) which were formed during the deposition process and embedded in the SiN_x films. White photoluminescence with multiple emission peaks was achieved for potential solid state lighting applications from multi-layered SiN_x films by changing the SiH₄/NH₃ ratio during the deposition process. This was attributed to a combination of Si quantum dots with different sizes within the different layers. Surface texturing of the thin film samples was conducted by potassium hydroxide (0.56%) etching the (100) Si substrate for 3~40 min at 80°C before deposition. The reflectivity of the etched samples decreased with increasing etch time due to increased surface roughness. The extraction efficiency of light emission from the textured SiN_x thin films was significantly improved, owing to a depression of the internal reflection and interference effects. In addition, the elimination of the multiple emission peaks by surface texturing significantly affected the color coordinates of the output spectrum.

Solid state lighting (SSL) has made substantial inroads into the aviation lighting market in recent years. In many aircraft applications, the unique characteristics of this technology make it superior to the light sources presently employed. However, the novelty of this technology also brings new challenges to successful implementation within rigorous aerospace environs. This paper provides an overview of how the advent of solid state lighting has benefited the aerospace lighting industry, examines some of the current applications and looks forward to future uses of SSL in the aviation market. The discussion will include an examination of aerospace requirements and how SSL technology meets those requirements. The authors will address some of the challenges presented by solid state light relative to the aerospace industry and explore how these issues can be overcome.

The use of RGB and RGBA LEDs in luminaires enables a variety of features, such as color temperature-controllable white light, that have not been available in traditional sources. The general illumination market requires that lamp chromaticity be accurately maintained, and therefore an advanced control scheme must be used. Feeding back tristimulus values alone is not enough to maintain precise color control, given the variability of LEDs during changes in ambient temperature, degradation over life, and manufacturing tolerances. In this paper, we discuss a solution based on photodiodes with color filters combined with feedforward temperature compensation and empirical LED data. We also discuss a method to maintain control feedback loop stability and accuracy over the full dimming range.

OLED technology may be excellently suitable for lighting applications by combining high efficiency, cost effective manufacturing and the use of low cost materials. Certain issues remain to be solved so far, including OLED brightness, color, lifetime, large area uniformity and encapsulation. Another aspect, that might be capable in addressing some of the mentioned issues, is OLED lighting electrical driving. We report on the design of a driving platform for OLED lighting test panels or substrates. It is intended for being a test environment for lighting substrates as well as demonstration/presentation environment. It is based on a 128-channel passive-matrix driver/controller ASIC OC2. Its key component is an MSP430-compatible 16-bit micro-controller core including embedded Flash memory (program), EEPROM (parameter), and RAM (data memory). A significant feature of the device is an electronic approach for improving the lifetime/uniformity behavior of connected OLED. The embedded micro-controller is the key to the high versatility of OC2, since by firmware modification it can be adapted to various applications and conditions. Here its application for an OLED lighting driving platform is presented. Major features of this platform are PC-control mode (via USB interface), stand-alone mode (no external control necessary, just power supply), on-board OLED panel parameter storage, flat geometry of OLED lighting panel carrier (board), AC and DC driving regimes, adjustable reverse voltage, dedicated user SW (PC/Windows-based), sub-tile patterning and single sub-tile control, combination of multiple channels for increasing driving current. This publication contains results of the project "High Brightness OLEDs for ICT & Next Generation Lighting Applications" (OLLA), funded by the European Commission.

Lightguide devices are commonly used in a large number of applications such as light-delivery systems, illumination, and displays. The general approach is to outcouple light from the lightguide without concern for its propagation properties within the guiding material. We introduce the concept of a lightguide with controlled numerical-aperture as it propagates within the guiding substrate and demonstrate the advantages with this approach, compared to other methods commonly used. We also demonstrate the application of our lightguide technology for general illumination with controlled light distribution and high efficiency.

There are many advantages that LEDs offer for use in general illumination. The use of LEDs in certain applications can provide improved energy efficiency. For example, in traffic lights in the United States, LED technology has taken over the market not only because of the energy savings as compared to standard incandescents, but also because of the reduced maintenance costs associated with bulb replacement and improved reliability. With useful lifetimes exceeding 40,000 hours or more, today's high flux LEDs can provide illumination solutions with replacement periods of 8 to 10 years or more. This paper will examine a bridge roadway lighting feasibility study which the authors' company recently undertook. The application required the LED units to reproduce the photometric performance of 64-inch (1.625m) fluorescent lamps. In addition, the LED units were required to survive a harsh, outdoor marine environment with an expected lifetime of 7 years or more. To achieve these results, a number of design elements were studied including: optimum heat dissipation in a sealed enclosure, ease of installation, and design of power supplies having expected lifetimes to match the LED light engines. Results of these studies will be discussed as well as illustrations of the designs chosen.

The use of LED backlighting for LCD displays requires careful binning of red, green, and blue LEDs by dominant wavelength to maintain the color gamuts as specified by NTSC, SMPTE, and EBU/ITU standards. This problem also occurs to a lesser extent with RGB and RGBA assemblies for solid-state lighting, where color gamut consistency is required for color-changing luminaires. In this paper, we propose a "six-color solution," based on Grassman's laws, that does not require color binning, but nevertheless guarantees a fixed color gamut that subsumes the color gamuts of carefully-binned RGB assemblies. A further advantage of this solution is that it solves the problem of peak wavelength shifts with varying junction temperatures. The color gamut can thus remain fixed over the full range of LED intensities and ambient temperatures. A related problem occurs with integrated circuit (IC) colorimeters used for optical feedback with LED backlighting and RGB(A) solid-state lighting, wherein it can be difficult to distinguish between peak wavelength shifts and changes in LED intensity. We apply our six-color solution to the design of a novel colorimeter for LEDs that independently measures changes in peak wavelength and intensity. The design is compatible with current manufacturing techniques for tristimulus colorimeter ICs. Together, the six-color solution for LEDs and colorimeters enables less expensive LED backlighting and solid-state lighting systems with improved color stability.

Application of light emitting diodes is expanding as the luminous output and efficiencies of these devices improve. At the same time, the number of LED package types is increasing, making it challenging to determine the appropriate device for use in lighting product designs. A range of factors should be considered when selecting a LED for an application including color coordinates, luminous efficacy, cost, lumen maintenance, application life, packaging and manufacturability. Additional complexities can be introduced as LED packages become obsolete and replacement parts must be selected. The replacement LED characteristics must be understood and assessed against the parameters of the original device, in order to determine if the change will be relatively simple or will force other end-product changes. While some characteristics are readily measured and compared, other factors, such as lumen maintenance, are difficult to verify. This paper will discuss the characteristics of a LED that should be considered during the design process as well as methods to validate these characteristics, particularly those which are not typically on data sheets or, are critical to the design and warrant additional validation. Particular attention will be given to LED lumen maintenance. While published manufacturer data typically provides temperature versus performance curves, the data may not be useful depending upon the application's operating environment. Models must be created to estimate the LED's junction temperature and degradation curve at the applied temperature in order to develop a more precise life estimate. This paper presents one approach to a LED device life and performance study designed with application environments in mind.

A study was conducted to determine the viability of an LED-based parking garage light. The requirements for this light were based on the Illumination Engineering Society of North America (IESNA) enclosed parking/driving lanes specifications. Three basic optical designs were compared. The first used no secondary optic, the second used a reflector optic, and the third used a lens optic. Based on the findings herein, the IESNA requirements could be met using approximately 121 1-watt LEDs of typical performance today. Compared to metal halide, high pressure sodium, and fluorescent lights the LED fixture would have a longer lifetime as well as equal or better color rendering index and energy efficiency. Although the energy consumption and the re-lamping frequency could be significantly less for an LED fixture, currently the initial cost of a fixture meeting the IESNA requirements would be more than several times higher than that of existing fixtures. LED cost per lumen is decreasing rapidly, however, it will likely take several years before a cost effective LED light can provide the same performance as metal halide, high pressure sodium, and fluorescent lighting in parking garage applications.

Unless coupled with some collimating optics, LED sources generally scatter with wide-angle Lambertian intensity profiles. The luminous output of such sources is not amenable to control and redistribution in an efficient manner. In this work we present the design and manufacturing of structures that are able to collect virtually all light from Lambertian LED sources and direct it towards diffusers engineered to illuminate specific regions of space in a controlled fashion. The resulting "engineered luminaire" is thus capable of highly efficient light control and can be applied to a wide variety of illumination situations such as general and architectural lighting.

Efficient white light LED systems with continuously tunable color temperature (CT) over a range of 3000 K to 6500 K are reviewed. Typically, white light sources have a fixed CT and color rendering index (CRI). White light with user-specified color temperatures is currently generated by solid-state systems with red green blue ("R/G/B"), red green blue amber ("R/G/B/A"), and warm white cool white ("WW/CW") LED combinations, but their performance is suboptimal for architectural lighting applications. We propose and discuss an LED module with a combination of warm white, green and blue ("WW/G/B") LEDs. In this scenario, the white LEDs have fixed intensity, while the blue and green LED intensities are adjusted to shift the LED module chromaticity along the blackbody locus. We also propose and discuss an LED module with a combination of red, green, blue, and cool white ("R/G/B/CW") LEDs. The white LEDs still have a fixed intensity, while the intensities of the red, green, and blue LEDs are again adjusted to shift the LED module chromaticity along the blackbody locus. The white LEDs ensure that an improved CRI is maintained in comparison to a simple "R/G/B" solution.

This paper demonstrates the strong enhancement of light extraction efficiency of light-emitting diodes (LEDs) by a novel three-dimensionally arranged micro-cavity. There are several optimal designed parameters, including chip dimensions, absorption coefficients, the shape of the micro-cavity and package are analyzed on the basis of a Monte-Carlo ray tracing simulation. The most important that studying includes GaN LEDs which are applied to various applications, including traffic signals, backlight system for LCD and outdoor illumination by white light LEDs. The functional of the three-dimensionally arranged micro-cavity is to make the light extraction from LED with high efficiency. The shape of micro-cavities are making like hexagon solids on the top view. The structure were evaluated and simulated by TracePro software respectively. The light extraction efficiency of LED can be greatly improved by three-dimensionally arranged micro-cavity. This study shows that the micro-cavities induced on the surface rather than that inside the LED greatly enhances the light extraction efficiency. This stipulation holds for both sapphire-based and Thin-GaN LEDs. The results indeed identify the attributes of the LED, which make it possible to achieve excellent luminance performance using a GaN-based approach from the LED of "three-dimensionally arranged micro-cavity". This structure was stringent expected to allow a high-efficiency LED, since the illumination systems needed for higher luminance energy can be added independently of the effects.

A three-dimensional thermal model of LED illuminating device is established by using the finite element method. The natural convective boundaries are applied on the lateral surfaces, and an equivalent convective boundary on the bottom surface is utilized to represent the real effects of heat sinks or fins on LEDs. In this paper, the dielectric layer of LED die bonding is discussed and the influences of external and internal thermal resistances are analyzed. When we enhance the external convective effect, the external thermal resistance is reduced obviously. The thermal conductivity of material and the thickness of dielectric layer are important factors on the internal thermal resistance. We may propose these results to design and develop the global principle for the heat-dissipating package of LED device to increase the performance of LED.

High-brightness, inorganic light-emitting diodes (LEDs) have been successfully utilized for edge-lighting of large displays for signage. Further interest in solid-state lighting technology has been fueled with the emergence of small molecule and polymer-based organic light-emitting diodes (OLEDs). In this paper, edgelit inorganic LED-based displays and state-of-the-art OLED-based displays are evaluated on the basis of electrical and photometric measurements. The reference size for a signage system is assumed to be 600 mm x 600mm based on the industrial usage. With the availability of high power light-emitting diodes, it is possible to develop edgelit signage systems of the standard size. These displays possess an efficacy of 18 lm/W. Although, these displays are environmentally friendly and efficient, they suffer from some inherent limitations. Homogeneity of displays, which is a prime requirement for illuminated signs, is not accomplished. A standard deviation of 3.12 lux is observed between the illuminance values on the surface of the display. In order to distribute light effectively, reflective gratings are employed. Reflective gratings aid in reducing the problem but fail to eliminate it. In addition, the overall cost of signage is increased by 50% with the use of these additional components. This problem can be overcome by the use of a distributed source of light. Hence, the organic-LEDs are considered as a possible contender. In this paper, we experimentally determine the feasibility of using OLEDs for signage applications and compare their performance with inorganic LEDs. Passive matrix, small-molecule based, commercially available OLEDs is used. Design techniques for implementation of displays using organic LEDs are also discussed. It is determined that tiled displays based on organic LEDs possess better uniformity than the inorganic LED-based displays. However, the currently available OLEDs have lower light-conversion efficiency and higher costs than the conventional, inorganic LEDs. But, signage panels based on OLEDs can be made cheaper by avoiding the use of acrylic sheet and reflective gratings. Moreover, the distributed light output and light weight of OLEDs and the potential to be built inexpensively on flexible substrates can make OLEDs more beneficial for future signage applications than the inorganic LEDs.

A field study was conducted at three clothing stores to validate previous laboratory findings indicating that colored LEDs used as background display lighting could: 1) lower the power demand of accent lighting by up to 50 percent; and 2) provide greater attention capture and visual appeal than current lighting practice. Blue LEDs provided a colored background for window mannequins by illuminating white backdrops. Eliminating fluorescent general lighting and reducing the number and wattage of halogen accent lamps in the display windows reduced the lighting power demand by up to 50 percent. During an eight-week period, more than 700 shoppers rated the attractiveness, eye-catching ability, comfort, and visibility of four different lighting conditions. The results of this field study showed that by introducing color contrast between the displayed objects and the background, the power demand of the accent lighting could be reduced by up to 50 percent without sacrificing visual appeal, visibility, ability to capture the attention of shoppers, and the ability to see the colors of the objects on display. Furthermore, the sales of the products on display were not affected by the 50 percent reduction in lighting.

Light-emitting diode (LED) technology is presently targeted to displace traditional light sources in backlighted signage. The literature shows that brightness and contrast are perhaps the two most important elements of a sign that determine its attention-getting capabilities and its legibility. Presently, there are no luminance standards for signage, and the practice of developing brighter signs to compete with signs in adjacent businesses is becoming more commonplace. Sign luminances in such cases may far exceed what people usually need for identifying and reading a sign. Furthermore, the practice of higher sign luminance than needed has many negative consequences, including higher energy use and light pollution. To move toward development of a recommendation for lighted signage, several laboratory human factors evaluations were conducted. A scale model of a storefront was used to present human subjects with a typical red channel-letter sign at luminances ranging from 8 cd/m² to 1512 cd/m² under four background luminances typical of nighttime outdoor and daytime inside-mall conditions (1, 100, 300, 1000 cd/m²), from three scaled viewing distances (30, 60, 340 ft), and either in isolation or adjacent to two similar signs. Subjects rated the brightness, acceptability, and ease of reading of the test sign for each combination of sign and background luminances and scaled viewing distances.