This PDF file contains the front matter associated with SPIE Proceedings Volume 7784, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

In this paper we investigate the utilization of a patterned photonic crystal layer positioned below the Multiple Quantum Well region of a p-side up LED to improve light extraction and investigate the benefit of adding additional top surface photonic crystal patterning to the same device. Performance for each design is evaluated in terms of angular extraction efficiency and far field angular beam profile for fixed lattice geometry and a range of etch depths. We show that a buried photonic crystal lattice improves extraction for emission angles below the critical angle for total internal reflection, and does not have a detrimental effect over the normal extraction cone of the LED. An improvement of (33% to 57% in extraction efficiency is obtained using a buried photonic crystal lattice alone. The introduction of additional top surface patterning has potential to further improve the extraction efficiency up to 73%, and to tailor the shape of the emission profile.

Motivated by opportunities in smart lighting, energy efficiency, and ubiquitous sensing, we present the design of polychromatic solid-state lighting controlled using a sensor network. We developed both a spectrally tunable light source and an interactive lighting testbed to study the effects of systems that adjust in response to changing environmental lighting conditions and users' requirements of color and intensity. Using both linear and nonlinear optimization, the setpoints of overdetermined systems (greater than three wavelengths) and the energy consumption of the network are adjusted according to the room's lighting conditions (e.g., lux and color temperature of multiple fixtures). Using these techniques, it is possible to maximize luminous efficacy or the color rendering index for a given intensity and color temperature. We detail the system modeling, design, optical calibration, and control theory required to modulate the luminous output and minimize wasted energy.

Light-emitting diodes operating on alternating current are gaining popularity in the LED industry, especially for lighting applications. Because junction temperature is a good predictor of LED performance, the availability of a method to accurately estimate the junction temperature of AC LEDs would be very useful. This study investigated a method in which a low reference current having a pulse width of less than several milliseconds was applied and the corresponding voltage across the device was measured and correlated to the junction temperature. Laboratory experiment data showed that the proposed method is a promising candidate for estimating AC LED junction temperature.

Thomas Edison is widely regarded as the greatest inventor in history and the most prominent individual behind the invention of the electric light. His impressive characteristics as an individual that led to his amazing success as an innovator continue to be an inspiration for researchers today. This paper considers how Edison might proceed in developing solid state lighting into a technology capable of displacing incumbent light sources, including his own incandescent lamps, then reviews some of the "Edison-like" contributions made to solid state lighting by the Next Generation Lighting research program at Georgia Tech.

Natural lithography is realized by spin-coating of nanoparticles. The surface textured LED s and nanorod structured LEDs have been made successfully. Concentrated radiation profiles of nanorod structured and surface textured LED are both observed. We fabricate these nano-structure by nature lithography method which use silica nanosphere as etching mask. The SiO₂ grown by PECVD is used as a space layer to realize the nanorod LED. Furthermore, we suggest a light guided concept of the highly concentrated phenomena. The highest output power density of nanorod LEDs is achieved. The reversed current of nanorod LEDs is also reduced down to nA level.

Due to the light scattering processes that take place within the color conversion elements (CCE) of phosphor converted light-emitting diodes (LEDs) and the rather different emission characteristics of the blue LED and the converted light, which have to be matched by the scattering processes, a better understanding of the underlying physical aspects is indispensable for device optimization. We give, based on optical ray-tracing, a comprehensive survey on the parameters that effect color conversion and light scattering within the CCEs of phosphor converted LEDs. Studies range from variations of the geometrical (height, width) to the compositional (concentration of the phosphor in the matrix material, differences of the refractive indices of the matrix and the phosphor materials, phosphor particle size) parameters and identify their respective impacts on the color temperatures and the luminous efficacies of the respective LEDs.

High quality InGaN-based LEDs have been grown on Si (111) substrates using an Al₂O₃ transition layer. Freestanding, fabricated LED devices were achieved by removing the Si substrate using selective area wet etching. Conventional device design was used for LED fabrication, in which p-type and n-type contacts are located at the same side of the epilayers. These LED devices were bonded to a dual in-line package (DIP), and epoxy was used to protect the front side of the epilayers thin films as well as the bonding wires. The Si substrate was removed by wet etching while the chip was mounted in the DIP which prevented the thin film from cracking or warping. Electroluminescence (EL) characteristics of the LED devices grown on ALD/Si were measured before and after substrate removal. No significant change in peak emission wavelength was observed, nor any change in EL intensity versus drive current. No degradation of electrical and optical properties was observed. This indicates that the devices were not damaged by the wet etching process. However, the luminescence intensity of devices both before and after wet etching did not increase beyond a drive current of ~60 mA due to inefficient heat dissipation. The process developed and the challenges involved in the larger area substrate removal process will be discussed which could be substantially beneficial to the future substrate transfer and packaging in the industrial fabrication of LED on silicon substrate.

Results on the achievable growth temperature as a function of the reactor pressure for the growth of InN by high-pressure CVD are presented. As the reactor pressure was increased from 1 bar to 19 bar, the optimal growth temperature raised from 759°C to 876°C, an increase of 6.6 °C/bar. The InN layers were grown in a horizontal flow channel reactor, using a pulsed precursor injection scheme. The structural and optical properties of the epilayers have been investigated by Raman spectroscopy, X-ray diffraction, and IR reflectance spectroscopy.

Larger chip size with higher injection current is used in high power and high brightness LEDs. Thermal management and good current spreading are critical issues in these high power applications, besides the requirement on higher internal and external quantum efficiency. The conventional top emitting configuration is not suitable because of the poor thermal conductivity of the sapphire substrate and poor light extraction efficiency. The substrate removal and flip-chip methods can provide much better heat dissipation but having concerns on the yield. In this paper, we reported a broad area side emission LEDs (BSLED) with a large length to width ratio of 5000um to 500um so as to have a comparable light emitting area with top/back emission LEDs in the same amount of GaN wafer area. Both top and backside of wafer are coated with metals as mirror reflectors and are attached to heat sinks for better heat dissipation. The L-I, I-V and polarization characteristics from fabricated BSLED showed it is more promising than conventional top emitting LED at the same size. The BSLED provides more flexibility in lighting device design and could be more suitable for certain application like LCD backlighting.

Rare earth (RE) elements are promising alternatives to transition metals (TMs) for use in developing a dilute magnetic semiconductor (DMS) for spintronics applications. Instead of relying on the d-shell electrons of the TMs as the magnetic element, the 4f electrons from the RE elements are used. The 4f RE elements can have larger magnetic moments as compared to 3d TMs, because the 4f orbits are localized and the direct coupling between the 4f ions is weak. There have been several reports of using RE elements for optoelectronic applications, as their various internal f-shell electronic transitions vary in energy from infrared to visible.

Since the introduction of LED technology into the general illumination lighting market, one desired feature has been the ability to replace the luminaire lamp in a similar manner to conventional sources (e.g. screw or plug in). Due to thermal management issues, successfully implementing this feature has proven difficult with many manufacturers simply integrating the LED sources into the luminaire. However, there are LED replacement lamp products on the market that manufacturers claim to be the equivalent of their conventional source counterparts. This paper will examine the relationships between lifetime, light output, source efficacy, thermal management and physical size for three common lamps: the MR-16, the A-19 (standard incandescent shape) and the PAR-38 (standard floodlight shape). The author will evaluate the physical size envelope for the three lamp types. Next, a theoretical model for maximum thermal dissipation to ambient will be determined. Then using data from LED manufacturers, junction temperature limits versus lifetime will be evaluated and used to determine maximum input power. This input power limit combined with manufacturer's data and assumed optical and electrical losses will be used to evaluate potential light output of the lamp and compared to conventional lamp outputs. Upper limits for light output will be determined.

In recent years, there has been considerable press coverage about the promise of Solid State Lighting (SSL). Despite this or perhaps because of the coverage, it can be difficult to separate hype from reality and set expectations for the near to medium term. The short answer is there are good SSL products on the market now and some poor ones. The good ones are getting better, more common, and more affordable. This paper will cover the basics of the key components that make up a luminaire which are LEDs (light emitting diode), power supply, optics, and thermo/mechanical subsystems. Each component will be reviewed with highlights as to what is important. These subsystems will then be considered as a system. Several methodologies for designing both spot and area luminaires will be discussed focusing on non-residential buildings. The topic of SSL lifetime will be discussed. Finally, trends will be explored to provide an understanding of the kinds of improvements one can expect and the timeframe over which they may occur.

The light-emitting diode (LED) is a rapidly evolving, energy-efficient light source technology that holds promise to address the increasing need for energy conservation. However, the common belief that a high-efficacy light source equates to lower energy demand in application is incorrect. Generally, when a new light source technology replaces an existing light source in an application and claims energy savings, the inherent assumption is that all of the requirements of the application are met. In the case of directional lighting applications, what matters ultimately is the amount of luminous flux illuminating the task area. Therefore, when quantifying the performance of a luminaire, ideally one must consider only the amount of flux reaching the task area and the total power demanded. The objective of this paper is to introduce an alternative concept, application efficacy. This paper will demonstrate the concept's usefulness and proposed metrics for three different lighting applications-under-cabinet task lighting, refrigerated display case lighting, and outdoor parking lot lighting-and show how it better relates to energy demand. Details of laboratory experiments and software analysis along with data are presented for the three applications.

Increased luminaire gamut as well as increase in luminous efficiency is found when the LED based luminaire is driven by a hybrid PWM/AM dimming technique. This technique is applicable to any n-chromaticity luminaire but it is especially suitable for trichromatic RGB luminaires that do not have inherent degrees of freedom. Diodes' properties under the hybrid dimming method were measured and used in nonlinear optimization routine to find the driving conditions that yield e.g. the highest possible efficacy for a given color point.

A high-quality white light source requires high luminous efficacy (lumens per input watt). Theoretically, in the "greenyellow" spectral region (with a peak wavelength at around 555 nm), the luminous efficiency (lumens per radiant watt) reaches a maximum based on the luminous efficiency function, V(λ), and can potentially generate high luminous efficacy. Unfortunately, the light-emitting diode (LED) suffers from low external quantum efficiency in the "greenyellow" region, thereby lowering the luminous efficacy value. Researchers have sought solutions such as nonpolar or semipolar InGaN/GaN LEDs. An alternative to generating green light is to use phosphor down-conversion by exciting a green emission phosphor with a near-UV or blue LED of higher external quantum efficiency. In this study, a SrGa₂Se₄:Eu²⁺ phosphor with peak emission wavelength at 555 nm was initially synthesized and followed by a systematic study of the post-synthesis annealing. The purpose of this study was to investigate how post-synthesis annealing conditions, including annealing temperature, annealing duration, and annealing ambient atmosphere, can affect phosphor performance. The phosphor performance was characterized in terms of external quantum efficiency and emission properties. How the external quantum efficiency of the phosphor can be further improved is also discussed.

Finding an energy efficient replacement of incandescent candle lamp has been a technical challenge. Compact fluorescent lamps, for example, can be miniaturized to fit the form factor of a candle lamp but they fail to reproduce its "sparkle" effect. Empowered by solid state lighting technology along with original optical design, Philips has successfully developed LED-powered candle lamps "Novallure" with great energy savings (2W power consumption with lumen output of 55 lumen) and the "butterfly" radiation pattern that mimics the sparkle effect from an incandescent candle lamp. With new high performance LED packages, novel under-cut prismatic optics and state-of-the-art electronic driver solution and thermal solution, we have developed a 2nd generation Novallure with breakthrough performance: a dimmable 2700K 136 lumen LED candle lamp with CRI 90.

The die-attached quality and the thermal transient characteristics of high power flip chip light emitting diodes (LEDs) are investigated using thermal transient tester. Various die-attached materials were utilized to compare the difference in their thermal resistances and long term performance. By applying accelerated aging stress, the deterioration rates at the die-attached layers were obtained. Numerical simulation provided further understanding of LED device temperature distribution and also revealed that the thermal variance at the die-attached interface can be recognized within only few milliseconds for the flip chip structure. The effects of bump arrangement and material were analyzed to achieve high temperature uniformity and low thermal resistance for high power LEDs.

As energy efficiency becomes more and more important, light-emitting diodes (LEDs) are a promising alternative to traditional lighting. Indeed, the energy efficiency of LEDs is still improving as their luminosity is modulated by current. Moreover, for applications such as exterior lamp posts, their small size, directionality, colors and high frequency response allow to combine them and provide design possibilities which are impossible with any other light source. However, as any lamp, LEDs have a lumen depreciation which is a function of both current and temperature. Thus, to take advantage of the full characteristics of LEDs, LED luminaire longevity strategies must be carefully studied and planned, especially since the IES and CIE guidelines state clearly that the luminaire must maintain the rated recommended light level until the end of the system's operating life. The recommended approach for LED luminaire specification is therefore to use the end-of-life light level when evaluating the luminaire. Different power supply strategies have been simulated to determine which one maximizes energy saving and lifetime. With these results, it appears that active control can save at least 25% in energy, but the best strategy cannot be determined because of uncertainties in luminosity degradation models.

Lighting plays an important role in supporting retail operations, from attracting customers, to enabling the evaluation of merchandise, to facilitating the completion of the sale. Lighting also contributes to the identity, comfort, and visual quality of a retail store. With the increasing availability and quality of white LEDs, retail lighting specifiers are now considering LED lighting in stores. The color rendering of light sources is a key factor in supporting retail lighting goals and thus influences a light source's acceptance by users and specifiers. However, there is limited information on what consumers' color preferences are, and metrics used to describe the color properties of light sources often are equivocal and fail to predict preference. The color rendering of light sources is described in the industry solely by the color rendering index (CRI), which is only indirectly related to human perception. CRI is intended to characterize the appearance of objects illuminated by the source and is increasingly being challenged because new sources are being developed with increasingly exotic spectral power distributions. This paper discusses how CRI might be augmented to better use it in support of the design objectives for retail merchandising. The proposed guidelines include the use of gamut area index as a complementary metric to CRI for assuring good color rendering.

Fully phosphor-converted LEDs (FpcLeds) with saturated emission have been realized in the green and amber spectral region. With the Lumiramic™ phosphor technology it is possible to achieve high package efficiency with minimum transmission of blue light from the primary LED source. This is done by keeping the scattering properties of the phosphor layer low while the phosphor thickness is chosen to fully convert all blue LED emission. It is shown that this can be done not only for optically isotropic Lumiramic materials like garnets, but also for oxonitridosilicate materials like the green emitting Europium doped SrSi₂O₂N₂, crystallizing in a triclinic lattice with three optical axes. The scattering power of the Lumiramic can be decreased to acceptable levels by increasing the size of the crystallites in the densely sintered ceramics. Light propagation is found to be described well with Mie scattering of mono-sized SrSi₂O₂N₂ spheres with refraction index differing by 0.07 to the refractive index of a SrSi₂O₂N₂ matrix material. Using this technology, the green-yellow gap of visible light emitting LEDs can be bridged and color tunable lamps with the efficiency and flux of today's white phosphor-converted LEDs become feasible.

High brightness InGaN/GaN multiple quantum well structures have been grown on sapphire substrates by metalorganic chemical vapor deposition, for wide range visible light emitting diode application. The compositions and sizes within quantum wells were designed according to the requirements on the LED performance. Samples were investigated by a variety of characterization techniques. Optimization of the growth parameters and process was realized and evidenced by high resolution X-ray diffraction measurements. Optical spectroscopic properties were further studied and quantum confined stokes shift was observed from room temperature and low temperature photoluminescence as well as time resolved photoluminescence measurements.

White light-emitting diodes (LEDs) have dramatically developed and gradually taken over from the conventional light source as the solid-state lighting during the last decade. It is now sufficient for illumination application in performance, while it is still insufficient in color quality. Especially, most of phosphor-converted white LEDs have the poor angular color homogeneity. In this study, we adopted a distinctive phosphor conformal coating technique in the packaging process to reduce the variance of correlated color temperature (CCT) among the packages and spatial CCT in the package. Also, to reduce the spatial CCT variance without considerable shrinkage of luminous efficacy, we applied submicrometer scale TiO2 powder as diffuser in the phosphor layer or in the encapsulation layer of white LED with a phosphor conformal coating layer and investigated the effects of titania diffuser on angular color homogeneity and optical performance. Regardless of the diffuser content, spatial CCT variance and luminous efficacy were decreased with the increase of the diffuser content. Nevertheless, among the conditions for achievement of the equivalent in color uniformity, the luminous efficacy in the case of 0.1 wt% diffuser mingled in the encapsulation layer was 20 % higher than in the case of 5 wt% diffuser mingled in the phosphor layer. These phenomena result from differences of light scattering loss caused by 10 times more volume of diffuser mixed in the phosphor layer than in the encapsulation layer.

In this contribution the relevant technological aspects of LED-based lamps for solid state lighting are discussed. In addition to general energy efficiency considerations improvements in LED chip technology and white light generation are presented.

Nowadays the demand for thermal standards for power LEDs is increasing. On one hand metrics for fair comparison of competing products are needed; on the other hand, designers of power LED-based applications need reliable and meaningful data for their daily work. Today's data sheet information does hardly meet any of these requirements. In 2008 the JEDEC JC15 committee on thermal standardization of semiconductor devices decided to take action and created a task group to deal with thermal standardization issues of power LEDs. CIE has also created two new technical committees (TC2-63, TC2-64) which also aim to address thermal issues during measurement of high brightness / high power LEDs. This paper deals with thermal issues that are specific to light emitting diodes by describing novel test methods which may form basis of new measurement guidelines or standards including combined thermal and radiometric measurement of LEDs. Thermal issues in connection with short pulse measurements of LEDs and some thermal aspects of LM80 tests are also discussed.

AlGaN epilayers with higher Al-compositions were grown by Metalorganic Chemical Vapor Deposition (MOCVD) on (0001) sapphire. Trimethylgallium (TMGa), trimethylaluminium (TMAl) and NH₃ were used as the source precursors for Ga, Al, and N, respectively. A 25 nm AlN nucleation layer was first grown at low-temperature of 590 °C at 300 Torr. Followed, Al_xGa_1-xN layers were grown at 1080 °C on low-temperature AlN nucleation layers. The heterostructures were characterized by a series of techniques, including x-ray diffraction (XRD), Rutherford backscattering (RBS), photoluminescence (PL), scanning electron microscopy (SEM) and Raman scattering. Precise Al compositions were determined through XRD, RBS, and SEM combined measurements. Room Temperature Raman Scattering spectra shows three major bands from AlGaN alloys, which are AlN-like, A₁ longitudinal optical (LO) phonon modes, and E₂ transverse optical (TO) band, respectively, plus several peak comes from the substrate. Raman spectral line shape analysis lead to an optical determination of the electrical property free carrier concentration of AlGaN. The optical properties of AlGaN with high Al composition were presented here.

A series of ZnO thin films with different thicknesses grown on sapphire substrates by metalorganic chemical vapor deposition (MOCVD) have been studied by different characterization techniques. The optical properties are investigated by photoluminescence (PL), optical transmission (OT) and 1st order derivatives, various angle scanning ellipsometry (VASE). Rutherford Backscattering (RBS) shows the atomic Zn:O ratios with a few percentage aviation from 1:1, and thicknesses in range of 10~230 nm, roughness layer with 10~30nm, which are corresponding to results from atomic force microscopy (AFM), and scanning electron microscopy (SEM). The optical and structure characterization measurements have confirmed the good quality of these epitaxial ZnO materials.

We presents a nanorods AlN films on sapphire substrate deposited at oblique-angle by a radio-frequency reactive magnetron sputtering. A nanorods AlN layer was employed as a buffer layer for a GaN-based LEDs to improve optoelectronic characteristics of LEDs. The diameter of the nanorods AlN buffer layer is in the range of 30-50 nm. Typical current-voltage characteristics of the GaN-based LEDs with a nanorods AlN buffer layer have a forward-bias voltage of 3.1 V at an injection current of 20 mA. The output intensity of LEDs initially increases linearly as the injection current increases from 10 mA to 150 mA. The light output power of the GaN-based LED with a nanoporous AlN layer was about 31% higher than that of a GaN-based LED without a nanoporous AlN layer at an injection current of 250 mA.

LEDs are already being used in monitors, and they have more recently appeared in plate displays. Therefore, this study investigated the effects of color temperature and luminous efficiency for RGB LEDs mixing with tuning voltage. The base voltages of red, green, and blue LEDs will be set up for the color temperature of 6500K(D₆₅ white light). These results exhibited that changing the voltage of red LED had the broader color temperature from 2000 K to 16000 K and low luminous variation from 27 to 40 lm /W than green and blue LEDs. Though the green LED had the low luminous variation from 25 to 40 lm /W but the color temperature only tuned from 2500K to 7500K. In contrast, though the blue LED had large color temperature from 4000K to 19000K but the luminous efficiency had rapid variation from 20 to 40 lm /W. The green LED was suitable for fine-tuning color temperature from 2500K to 7500K. The blue LED had rapid variation of color temperature from 4000K to 19000K so it could only suitable for high-color temperature modulation. The color shifts (Δuv) of red and green LEDs were the same variation with color temperature but not for blue LED.

The capability of high-power nitride-based light-emitting diodes (HPLED) to withstand electrostatic discharge (ESD) is very important key index due to the horizontal structure of the insulating property of the sapphire substrate. However, it is difficult to real-time monitor the damage caused by the ESD stress because it occurred in a very short period. Current-voltage (I-V) curves and electroluminescence (EL) spectrum were applied to study the change during the series ESD stress. Time-resolved optical beam induced current (TR-OBIC) was used to analyze the characteristics of the delay time between normal region and the defect point caused by ESD stress. Transmission electron microscopy (TEM) was used to compare to the difference in the distribution of damage region and investigate the failure modes. During the series ESD stresses, V-shaped pits suffered from the high electrical field and the distance from multi-quantum well (MQW). The bottom of V-shaped defect would be one of index to assess the ESD endurance of LED chips.

Light emitting diode (LED) is an environmental-friendly product and could be a main lighting source in future. The research was to design a suitable LED lampshade for the street lighting. The radiation characteristic was required to be a rectangular distribution at the divergence-angle ratio of 7:3 for the x and y directions. Hence a design of two cylindrical lenses on the lampshade was used for the lighting distribution. Then an optimal simulation of these curvatures was done for the luminous distribution and efficiency. Final we got a rectangular lighting of the divergence-angle ratio of 7:3 and the radiator characteristic of bat-wing. The tolerance analyses of LED source distances were done on the x, y and z directions. The z direction was more sensibility than x and y directions for luminous efficiency and its tolerance must be kept under ±0.5mm for the illumination efficiency to be over 95%. Anyway, the similar extent could reach to 98.46% by Normalized Cross Correlation (NCC) between experimental and simulation and the error extent could reduce to 6.87% by Root Mean Square (RMS) error mode. The total luminance efficiency could reach to 92% without AR coating.

The polycrystalline BaGd_2-xO₄: Tb_x (x = 0.00 - 0.10) phosphors have been prepared by conventional high temperature solid state reaction method. All the prepared samples were characterized by powder XRD and EDS techniques. The photoluminescence (PL) and thermally stimulated luminescence (TSL) studies of these materials were investigated. For PL studies the samples were excited with 263 nm UV light. All the samples showed strong green emission at 543 nm due to ⁵D₄→⁷F₅ transition of Tb³⁺ ions. PL peak intensity was found to increase with increasing dopant concentration. For TSL studies, these samples were γ-irradiated with different dose rates using ⁶⁰Co source. TSL of these phosphors showed a sharp glow peak with peak maxima at 394 K. It is found that the incorporation of terbium activator in BaGd₂O₄ host lattice resulted in the increase of TSL intensity. The luminescence results of these materials shows that these are promising candidates for new green emission phosphor.