This PDF file contains the front matter associated with SPIE Proceedings Volume 8123, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

To encourage energy-efficient light sources, many governments around the globe have introduced legislation to phase out the incandescent lamp for general illumination. The United States enacted the Energy Independence and Security Act of 2007 that introduced minimum efficiency standards for lighting that will eliminate some incandescent lamps in the range of 40 W to 100 W by 2014. This begs the question: Is solid-state lighting ready to handle the incandescent phaseout? There is no doubt today that LED technology has advanced to a stage where it can cater to many lighting applications, including A-lamp replacements up to 60 W. However, several challenges must still be addressed before white LED based A-lamp replacements are adopted broadly in the general lighting market. The LED lighting community is actively seeking answers to many of the technical and market challenges. This paper discusses the current state of LED lighting technology, where it is in terms of performance, the challenges to be overcome, and the considerations needed if LED lighting is to succeed in the market for incandescent replacement lamps.

This paper describes both the optical development of an LED-based sports lighting system and the results of the application of the system to an actual sport field. A traditional sport lighting fixture is generally composed of a single 1500 watt High Intensity Discharge (HID) light source with reflectors used to control the light distribution. The efficacy of the HID light source is equivalent or nearly equivalent to most LED light sources, putting LEDs at a large cost disadvantage in a high light output application such as sports lighting due to the number of LEDs and supporting components required to run an LED system. To assess the feasibility and applicability of LEDs in a sports lighting application, an LED-based sport light has been developed and installed on a small soccer field specified to have an average maintained illuminance level of 30 footcandles. An existing HID sport lighting system was also installed on the same size soccer field adjacent to the LED field with the same average footcandle level for comparison. Results indicate that LEDs can provide equivalent average illumination; however the LED source and system component cost is substantially higher. Despite the high cost, it was found that improved optical control afforded by the optical design used in the system provides a significant improvement in offsite wasted spill light, glare control, and on field uniformity. This could provide an advantage for LED systems.

With the rapid development of various types of digi-readers, such as i-Pad, Kindle, and so on, non-self-luminous type has an advantage, low power consumption. This type of digi-reader reflects the surrounding light to display so it is no good at all to read under dim environment. In this paper, we design a LED lamp for a square lighted range with low power consumption. The e-book is about 12cm x 9cm, the total flux of LED is 3 Lm, and the LED lamp is put on the upper brink of the panel with 6cm height and 45 degree tilted angle. For redistributing the energy, the LED lamp has a freeform lens to control the light of small view angle and a non-axisymmetrical reflector to control the light of large view angle and create a rectangular-like spot. In accordance with the measurement data, the proposed optical structure achieves that the power consumption of LED light source is only 90mW, the average illumination is about 200 Lux, the uniformity of illumination is over 0.7, and the spot is rectangular-like with precise light/dark cutting-off line. Our designed optical structure significantly increases the efficiency of light using and meets the environmental goal of low energy consumption.

Digitally controlled solid state lighting systems can afford a range of different qualities of light, adjustable to users' requirements. Sensor networks allow lighting changes to be actuated in response to the location, activities, and paths of the occupants. This paper reports initial results of an ongoing research to explore strategic control of a tunable LED system, in response to a preliminary activity recognition platform, as well as the associated human factors. Tunable LED panels connected to a sensor network were installed to illuminate three distinct occupied spaces: a private office, a public office space and a corridor at MIT Media Lab. Human factors experiments were conducted to assess visual acceptability under changing lighting conditions. In the first phase variations in color rendering were applied to verify perception of subtle changes in white lighting. Results from this phase indicate that it is possible to correlate activities with sensitivity to spectral change. In the second phase the question is how colored light can be used for energy savings and as a communication medium in these commercial spaces.

We report on the development and experimental analysis of an LED lighting module for use in a high-end food lighting environment which puts high demands on color homogeneity and color rendering. The system is built from highly reflecting and partly scattering PVD coated metal reflector sheet that has limited deformability and uses RGBW LEDs. We develop an optical design that is adapted to allow for color mixing and to take into account manufacturing constraints and include this into a prototypical module. Results of measurements and field tests are in good agreement with simulations.

Based on energy savings trend, LED has been developing as the main force of the future lighting, especially the road lighting. For controlling the intensity distribution of LED, the concept of freeform design has been proposed in many articles with transmission or reflection components but mainly focus on axial symmetrical types or dual axial symmetrical types. We, in this paper, design a non-axisymmetrical freeform system applying in a short LED street lamp whose dimension is 10cm (W) x 10cm (L) x 7cm (H) that has an advantage, easy maintaining. For coordinate transformation and simplifying the non- axisymmetrical system, we create two virtual surfaces and design the slope of each discrete point on the freeform surface to control the light path between the two virtual surfaces and avoid the total internal reflection. The short street lamp has four LEDs to light 3m square and each LED light a triangle area. According to the simulation results, the uniformity of illumination is 1:3 and the optical efficiency is more than 80% that meet the legal requirements of street lamp. In short, to reduce manufacturing and maintenance costs, the proposed design is appropriate to use in the actual lighting on the road and to replace the traditional street lamps.

Energy efficiency has been the primary driving force for solid state lighting to replace wasteful incandescent lamps by light emitting diodes (LEDs). Recently, rising cost for rare earth metals has redoubled the push to also replace fluorescent and compact fluorescent lighting. Phosphors in fluorescent lamps heavily rely on rare earth metals and even first generation LEDs use such phosphors, albeit at much lower quantities. The role of phosphors to expand a narrow wavelength source into a wider spectrum is a very lossy process in itself and can be circumvented altogether by second generation LEDs, where the full visible solar spectrum is directly replicated by direct emitting LEDs. We here report progress of our work towards this goal, in particular by the development of high brightness direct emitting green group- III nitride LEDs.

A set of AlGaN epilayers were grown on sapphire (0001) substrate by MOCVD, with intermediate growths of low/high temperature AlN nucleation layers. Variable flow rates of trimethylindium (TMIn), 0, 50 and 500 sccm were introduced during growth. Three AlGaN samples were originally designed with similar Al composition of ~20%. Rutherford backscattering (RBS), RT and 10-300K photoluminescence (PL) were used for analyzing the microstructure of thin films. The Al content was calculated to decrease with increasing the In-flow rate. Main PL bands spread over 310-350 nm with peaks in 320-335 nm. PL (10-300K) exhibited anomalous temperature dependent emission behavior (specifically an S-shaped shift, i.e. red-blue-red shifts) of the AlGaN related PL emission. Carriers transfer between different luminescent centers. Abnormally high activation energy was obtained, which shows that the excitons are not in the free states. Raman Scattering and spectral line shape analysis leaded to an optical determination of the electrical property free carrier concentration of AlGaN. Our results on In-doped AlGaN provide useful information for designing UV-LEDs.

Highly efficient InGaN/GaN LEDs grown on 4- and 8-inch silicon substrates comparable to those on sapphire substrates have been successfully demonstrated. High crystalline quality of n-GaN templates on Si were obtained by optimizing combination of stress compensation layers and dislocation reduction layers. The full-width at half-maximum (FWHM) values of GaN (0002) and (10-12) ω-rocking curves of n-GaN templates on 4-inch Si substrates were 205 and 290 arcsec and those on 8-inch Si substrate were 220 and 320 arcsec, respectively. The dislocation densities were measured about 2~3×10⁸/cm² by atomic force microscopy (AFM) after in-situ SiH₄ and NH₃ treatment. Under the unencapsulated measurement condition of vertical InGaN/GaN LED grown on 4-inch Si substrate, the overall output power of the 1.4×1.4 mm² chips representing a median performance exceeded 504 mW with the forward voltage of 3.2 V at the driving current of 350 mA. These are the best values among the reported values of blue LEDs grown on Si substrates. The measured internal quantum efficiency was 90 % at injection current of 350 mA. The efficiency droops of vertical LED chips on Si between the maximum efficiency and the efficiency measured at 1A (56.69 A/cm²) input current was 5%.

We have performed a comparative structural and optical investigation of InGaN/GaN MQW LED wafers grown on (1122) facet GaN/sapphire templates by Metalorganic Chemical Vapor Deposition. The effect of the growth time of epitaxial lateral overgrowth GaN with (11 2 2) facets on the structural and optical properties were investigated via photoluminescence (PL), PL excitation, time-resolved PL, Raman and SEM measurement on two typical InGaN MQW samples. From temperature dependence PL measurement, we can find that these two samples both exhibit two distinguish peaks attributed to quantum wells with wide range wavelength. Raman E₂ (high) signals revealed a partially relaxation of compressive stress in the facet GaN template. Experimental observations have revealed: (a) a Stokes shift between the emission peak energy and absorption edge and (b) a red shift behavior of emission with decay time (equivalently, a rise in decay time with decreasing emission energy). The large Stokes shift can be attributed to the quantum confined Stark effect (QCSE). The lower-energy side of the InGaN main emission peak is governed mainly by carrier generation in the GaN barriers and subsequent carrier transfer to the InGaN wells. Different amounts of Stokes shift indicate the interface imperfection from longer growth time of epitaxial lateral overgrowth GaN with (1122) facets. Temperature dependence of PL decay time τPL shows an interesting behavior of τ_PL with temperature.

The term "daylighting" is used in various ways, on one hand in a more architectural sense, i.e. using existing daylight to illuminate spaces, and on the other, more recently, for using light sources to replicate daylight. The emergence of solid state lighting (SSL) opens up a large number of new avenues for daylighting. SSL allows innovative controllability of intensity and color for artificial light sources that can be advantageously applied to daylighting. With the assistance of these new technologies the combination of natural and artificial lighting could lead to improvements in energy savings and comfort of living beings. Thus it is imperative to revisit or even improve daylighting research so that building networks of the future with their sensor, energy (e.g. HVAC) and lighting requirements can benefit from the emerging capabilities. This paper will briefly review existing daylighting concepts and technology and discuss new ideas. An example of a tunable multi-color SSL system will be shown.

The lumen degradation and chromaticity shift in glass and silicone based high-power phosphor-converted white-emitting diodes (PC-WLEDs) under accelerated thermal tests at 150°C, 200°C, and 250°C are presented and compared. The glass based PC-WLEDs exhibited better thermal stability than the silicone by 4.8 time reductions in lumen loss 6.8 time reductions in chromaticity shift at 250°C, respectively. The mean-time-to-failure (MTTF) evaluation of glass and silicone based high-power PC-WLEDs in accelerated thermal tests is also presented and compared. The results showed that the glass based PC-WLEDs exhibited higher MTTF than the silicone by 7.53 times in lumen loss and 14.4 times in chromaticity shift at 250°C, respectively. The thermal performance of lumen, chromaticity, and MTTF investigations demonstrated that the thermal stability of the glass based PC-WLEDs were better than the silicone. A better thermal stability phosphor layer of glass as encapsulation material may be beneficial to the many applications where the LED modules with high power and high reliability are demanded.

Accelerated ageing tests (1500h/85°C/30mA) performed on packaged InGaN/GaN MQW LEDs have reported a fluorescence shift of silicone oil responsible for optical losses. Electrical and optical characteristics highlight a 65% loss of optical power. Through measurements of the copolymer silicone coating fluorescence emission spectra, we demonstrate that the polymer fluorescence (induced from the blue light emitted from the chip) enlarges the LED emission spectrum (7%) and shifts central wavelength (5 to 7 nm). To understand such a fluorescence shift, Attenuated Total Reflection, Nuclear Magnetic Resonance (NMR), mass spectrometry and Differential Scanning Calorimetry (DSC) have been performed. The copolymer molecular structure has been affected after ageing. Actually, NMR and Mass spectrometry evidences the disappearance of low molecular weight molecules and the presence of high molecular weight molecules after ageing. Such a mechanism is associated with the polymerization of the silicone oil after ageing. Indeed, DSC has confirmed that silicone oil polymerization process is activated by temperature. Finally, both polymerization of the silicone oil due to temperature and fluorescence shift activated by photothermal process have been identified as the main failure mechanisms responsible for optical power degradation.

Light-emitting diodes operating on alternating current (AC) are gaining popularity in lighting applications. The junction temperature of an LED significantly influences performance. Although there are many proven methods for estimating the junction temperature of direct current (DC) LEDs, only a few methods have been proposed for AC LEDs. Two different methods were investigated and analyzed for their accuracy in estimating AC LED junction temperature: a low reference current pulse used to measure the voltage across the junction, and an active cooling system to recover the first half cycle current (rms). Method details are provided. The results suggest that the voltage drop method for AC LEDs is a viable method to estimate junction temperature.

A novel method is presented to inject the light of millimeter-sized high-brightness blue LEDs into light guides of submillimeter thickness. Use is made of an interference filter that is designed to pass only those modes that will propagate in the light guide by total internal reflection. Other modes are reflected back to the LED cavity and recycled, leading to an increased brightness. With this method a collimator has been designed and made that is only 1mm thick, with a diameter of 6.5mm. It creates a beam of 26deg Full Width at Half Maximum. Presently, collimators with these characteristics have a thickness of 10-20mm and a diameter of 20-30mm and require careful mounting and alignment. The new collimator contains a 4.5micron thick interference filter made of 54 layers of Nb₂O₅ and SiO₂ layers. The filter is optically coupled to the LED with Silicone adhesive which makes the configuration very robust. A cylindrical lightguide, tapered from 6.5mm to 2.5mm diameter and 1mm thick captures the light that passes the filter, folds the light path and redirects the beam. Measurements on collimator prototypes show good agreement with the designed characteristics. This promising approach enables much more compact collimators optics that offer material cost savings and design freedom.

In this paper we design a freeform lens according to the LED light distribution curve so that the light rays emitted from a LED through the lens can achieve high uniformity and efficiency on the prescribed target plane. Because the model is of rotational symmetry, we consider just a 2-D lens shape and then sweep to get the 3-D result. Here a procedure based on the Snell's law and edge-ray principle for designing the freeform lens is proposed. First of all, we analyze the LED intensity distribution and subdivide it into parts. Then we calculate the zones on the target plane where the subdivided light rays should be distributed to. Finally we use an approximate analytic method to construct the freeform lens. After constructing the freeform lens, we simulate for the optical model by using the ray-tracing software LightTools^®. The simulation results show that the Cree XLamp XR-E LED light source through the freeform lens can achieve up to 94.8% uniformity and 89.1% efficiency including Fresnel losses for a 1 m distance away and 1 m radius of circular illumination plane.

In recent trend, LED begins to replace traditional light sources since it has many advantages, such as long lifespan, low power consumption, environmentally mercury-free, broad color gamut, and so on. According to the zonal lumen density requirement of ENERGY STAR, we design a triangular-prism structure for LED light tube. The optical structure of the current LED light tubes consists of the array of LED and the semi-cylindrical diffuser in which the intensity distribution of LED is based on Lambertian and the characteristics of diffuser are BTDF: 63%, transmission: 27%, and absorption: 10%. We design the triangular-prism structure at the both sides of the semi-circular diffuser to control the wide-angle light and use the Taguchi method to optimize the parameters of the structure that will control the 10.41% of total flux to light the area between 90 degree and 135 degree and to avoid the total internal reflection. According to the optical simulation results, the 89.59% of total flux is within 90 degree and the 10.41% of total flux is between 90 degree and 135 degree that match with the Solid-State Lighting (SSL) Criteria V. 1.1 of ENERGY STAR.

The optical distribution of a white organic light-emitting diode (WOLED) with 10x10mm² emitting area was experimentally investigated and profiled by using a microscopic goniometer associated with energy analyzer in which the optical power on focusing spot in emitting area can be independently analyzed. Its optical distribution profile can be established by the interrelation between the relative intensity and position around emitting area. WOLED has become a potential planar lighting source due to its unique device structure consisted of multiple organic layers sandwiched by cathode and anode electrodes on glass substrate. The optical distribution of a WOLED planar lighting source is ideally expected to be uniform distribution around emitting area. Our experimental result measured from two independent WOLED samples reveals a unique distribution in which the relative intensity in central area is higher than that near the edge around emitting area. Its optical profile is similar to Gaussian distribution rather than uniform distribution as observed by naked eyes. It is also indicated that the optical profile of a WOLED planar lighting source is analogous to a point lighting source in microscopic point of view.

Faceted freeform reflectors were designed for intelligent street lighting with LED cluster arrays for main traffic roads. Special attention was paid to achieve highly efficient illumination on both wet and dry road surfaces. CIE reflection tables W4 and C2 were applied in the simulation for these two conditions, respectively. The reflector design started with plane facets, then - to avoid artifacts from the images of the individual LEDs - plane facets were replaced with cylindrical facets. To get even more flexibility for the design and optimization, freeform facets were employed, modeled by extruding two different conic curves together. Besides of achieving well-proportioned road luminance distribution, the basic shapes of the reflectors were formed to control stray light caused by multiple reflections within the reflector and by reflection of light from neighbor clusters within the cluster array. The merit functions include useful transmission of light to the road as well as overall and lengthwise uniformity according to road illumination standards. Due to the large amount of variables, the optimization was carried out sequentially facet by facet. The design loops included compromising with manufacturing limitations for plastics molding and thorough analysis of conformity with DIN EN 13201 standards for ME road lighting classes. The calculated reflector profiles are realized by plastic injection molding.

We report the fabrication of mechanical lift-off high quality thin GaN with Hexagonal Inversed Pyramid (HIP) structures for vertical light emitting diodes (V-LEDs). The HIP structures were formed at the GaN/sapphire substrate interface under high temperature during KOH wet etching process. The average threading dislocation density (TDD) was estimated by transmission electron microscopy (TEM) and found the reduction from 2×10⁹ to 1×10⁸ cm^-2. Raman spectroscopy analysis revealed that the compressive stress of GaN epilayer was effectively relieved in the thin-GaN LED with HIP structures. Finally, the mechanical lift-off process is claimed to be successful by using the HIP structures as a sacrificial layer during wafer bonding process.

For InGaN/GaN based nanorod devices using top-down etching process, the optical output power is affected by non-radiative recombination due to sidewall defects (which decrease light output efficiency) and mitigated quantum confined Stark effect (QCSE) due to strain relaxation (which increases internal quantum efficiency). Therefore, the exploration of low-temperature optical behaviors of nanorod light emitting diodes (LEDs) will help identify the correlation between those two factors. In this work, low-temperature EL spectra of InGaN/GaN nanorod arrays was explored and compared with those of planar LEDs. The nanorod LED exhibits a much higher optical output percentage increase when the temperature decreases. The increase is mainly attributed to the increased carriers and a better spatial overlap of electrons and holes in the quantum wells for radiative recombination. Next, while the nanorod array shows nearly constant peak energy with increasing injection currents at the temperature of 300K, the blue shift has been observed at 190K. The results suggest that with more carriers in the quantum wells, carrier screening and band filling still prevail in the partially strain relaxed nanorods. Moreover, when the temperature drops to 77K, the blue shift of both nanorod and planar devices disappears and the optical output power decreases since there are few carriers in the quantum wells for radiative recombination.

The inherent control flexibility implied by solid-state lighting - united with the rich details offered by sensor networks - prompts us to rethink lighting control. In this research, we propose several techniques for measuring work surface illuminance and ambient light using a sensor network. The primary goal of this research is to measure work surface illuminance without distraction to the user. We discuss these techniques, including the lessons learned from our prior research. We present a new method for measuring the illuminance contribution of an arbitrary luminaire at the work surface by decomposing the modulated light into its fundamental and harmonic components.

Continuing developments in LED lighting are leading to more lighting products for illumination in LED fixtures for the residential, commercial, and industrial facilities. Most of the research in the past ten years has been aimed at developing LEDs with higher brightness, higher efficacies, good color performance and longer life. Many efforts have been accomplished to develop LED driver circuits to drive LED arrays, even drivers that are dimmable. Manufacturers are increasing their level of concern with the performance and life of the whole LED product with a renewed emphasis on reliability. Reliability for LED products not only involves thermal management, fixture design, and driver loading but also how products respond to electrical disturbances that occur in the building electrical environments where the products must function. EPRI research has demonstrated that the immunity of LED lighting systems to common everyday electrical disturbances is critical to establishing the reliability needed to ensure expected performance and for their survival during product life. Test results showing the application of voltage surges, transients, and sags among other disturbances will be presented. This paper will discuss the application of the results of EPRI research in this area, the test protocol associated with EPRI system compatibility concept, examples of how applying the concept has identified reliability problems in LED products, and how the reliability of these LED systems can be easily improved.

Versatile spectral power distribution of solid-state light sources offers vast possibilities in color rendition engineering. The optimization of such sources requires the development and psychophysical validation of an advanced metric for assessing their color quality. Here we report on the application and validation of the recently introduced statistical approach to color quality of illumination. This new metric uses the computational grouping of a large number of test color samples depending on the magnitude and direction of color-shift vectors in respect of just perceived differences of chromaticity and luminance. This approach introduces single-format statistical color rendition indices, such as Color Fidelity Index, Color Saturation Index and Color Dulling Index, which are the percentages of test color samples with particular behavior of the color-shift vectors. The new metric has been used for the classification of practical phosphor conversion white light-emitting diodes (LEDs) and polychromatic LED clusters into several distinct categories, such as high-fidelity, color saturating, and color dulling light sources. We also report on the development of the tetrachromatic light source with dynamically tailored color rendition properties and using this source for the psychophysical validation of the statistical metric and finding subjective preferences to the color quality of lighting.

Alternating-current (AC) driven light-emitting diodes (LEDs) have become the trend of solid-state lighting (SSL) products. The junction temperature is an important index of LEDs reliability and efficiency. In other words, with proper thermal management of AC LEDs lighting products, the high performance of SSL products will be achieved. In order to obtain the junction temperature, we study and compare two published evaluating methods differentiating between the measurements of DC and AC in this paper. The first method is in which a low reference current having a pulse width was applied and the corresponding voltage across the device was measured and correlated to the junction temperature (Tj). The second method is using an active heat sink for recovering the root mean square (RMS) current of the first half cycle to estimate the junction temperature. The experimental evidence showed different aspects and variations of evaluating the AC LEDs junction temperature. The variations of evaluating junction temperature were caused by the switch time and phase of different source measurements in the first method and the capture time of the first half cycle in the second method. With proper capture time, the rising junction temperature in the second method might be negligible.

We investigated the structural and optical characteristics of nonpolar a-plane (11-20) GaN structure grown on TiO₂ nanoparticles (NP)-coated r-plane sapphire by spin coating method. The surface morphology without any observable inverse pyramidal pits was observed by atomic force microscopy (AFM) measurement. Transmission electron microscopy (TEM) analysis revealed that the threading dislocations (TDs) and basal plane stacking faults (BSFs) densities were around 4.5 × 10⁹ cm^-2 and 3.1 × 10⁵ cm^-1, respectively. It was also found that the broadening of x-ray rocking curves (XRC) full width at a half maximum (FWHM) in Si-doped a-plane GaN on the TiO₂ NP-coated r-plane sapphire was affected by the tilt and twist of mosaic crystals. The photoluminescence (PL) intensity of TiO₂ NP-related MQWs sample at 295 K was approximately 18 % higher than that of the reference sample. This implied that the improved PL intensity was attributed to scattering of light by TiO₂ NP and InGaN/GaN MQWs interface of high quality.

We report on blue-white luminescence from amorphous silicon oxycarbide a-SiC_xO_y≤1.68 (0.25<x<0.36) thin films, synthesized by thermal chemical vapor deposition (TCVD) process. The luminescence from SiC_xO_y was found to exhibit a broad band in the blue-violet to near infrared range (370 - 750 nm), visible to the naked eye in a bright room. The effects of carbon concentration (8.4 at.% < C < 13.6 at.%) in the material and post-deposition annealing treatments (Ar and forming gas 5% of H₂ ambient up to 1100°C) on the observed luminescence were studied. The emission intensity slightly decreased with increasing carbon content but was appreciably enhanced in the samples following post-deposition annealing treatment in forming gas 5% of H₂ ambient.

In this study, we would like to tune the color temperature of the high power phosphor Light-Emitting Diodes (LEDs) with the single LED of red, green, yellow and blue, respectively. The starting color temperature of the white phosphor LED will be set at 7500K (D75 white light), then changing the voltage of the single LED of the red, green, yellow and blue, respectively, to find the best tuning function for the color temperature and luminous efficiency. These results exhibited that changing the voltage of red LED had the broader color temperature from 7500 K to 1500 K and low luminous variation from 54 to 41 lm /W than green and blue LEDs. Though the green and yellow LEDs had the low luminous variation from 47 to 51 lm /W and from 40 to 47 lm /W, respectively, but the color temperature of green and yellow LEDs could only fine turn from 7500K to 8200K and 4700K to 7500K, respectively. The luminous efficiency had rapid variation from 27 to 42 lm /W and out of the color temperature of 20000K for the voltage tuning of blue LED. Therefore, the voltage tuning of red LED could show the warm color temperature for the human life. The variation of color shifts (Δuv) of red and green LEDs changed from small to large with the increasing of the enhanced voltage. But the variation of Δuv of the yellow and blue LED changed nothing with the increasing of the enhanced voltage.

In this paper, we use a Finite-Difference Time-Domain GaN LED model to study constant wave (CW) average power of extracted light. The structure simulated comprises of a 200nm-thick p-GaN substrate, 50nm-thick MQW, 400nm-thick n-GaN substrate, and a 200nm n-GaN two-dimensional Photonic Crystal(2PhC) grating. We focus on optimizing three design parameters: grating period (A), grating height (d), and fill factor (FF). In the primary set of simulations, we fix the fill factor at 50% and simulate ten different grating periods (100 to 1000nm in steps of 100nm) and four different grating heights (50 to 200nm in steps of 50nm), and calculate the average power output of the device. The results from these simulations show that for both conical and cylindrical gratings, the maxmium light extraction improvement occurs when A =100nm. In the second set of simulations, we maintain a constant grating period A = 100nm and sweep the fill factor from 25 to 75%. The results of these simulations show that the fill factor affects clyindrical and conical gratings differently. As a whole, we see that the nano-structure grating mostly depends on period, but also depends on height and fill factor. The grating structure improves light extraction in some cases, but not all.

A graded-composition electron blocking layer (GEBL) with aluminum composition increasing along [0001] direction was designed for c-plane GaN-based light-emitting diodes (LEDs). The simulation results demonstrated that such GEBL can effectively enhance the capability of hole transportation across the EBL as well as the electron confinement. Consequently, the LED with GEBL grown by metal-organic chemical vapor deposition exhibited better electrical characteristics, and much higher output power at high current density, as compared to conventional LED. Meanwhile, the efficiency droop was reduced from 34% in conventional LED to only 4% from the maximum value at low injection current to 200 A/cm².

We investigate the optical and electrical characteristics of the GaN-based light emitting diodes (LEDs) grown on Micro and Nano-scale Patterned silicon substrate (MPLEDs and NPLEDs). The transmission electron microscopy (TEM) images reveal the suppression of threading dislocation density in InGaN/GaN structure on nano-pattern substrate due to nanoscale epitaxial lateral overgrowth (NELOG). The plan-view and cross-section cathodoluminescence (CL) mappings show less defective and more homogeneous active quantum well region growth on nano-porous substrates. From temperature dependent photoluminescence (PL) and low temperature time-resolved photoluminescence (TRPL) measurement, NPLEDs has better carrier confinement and higher radiative recombination rate than MPLEDs. In terms of device performance, NPLEDs exhibits smaller electroluminescence (EL) peak wavelength blue shift, lower reverse leakage current and decreases efficiency droop compared with the MPLEDs. These results suggest the feasibility of using NPSi for the growth of high quality and power LEDs on Si substrates.

We consider the energy-saving potential of solid-state street lighting due to improved visual performance, weather sensitive luminance control and tracking of pedestrians and vehicles. A psychophysical experiment on the measurement of reaction time with a decision making task was performed under mesopic levels of illumination provided by a highpressure sodium (HPS) lamp and different solid-state light sources, such as daylight and warm-white phosphor converted light-emitting diodes (LEDs) and red-green-blue LED clusters. The results of the experiment imply that photopic luminances of road surface provided by solid-state light sources with an optimized spectral power distribution might be up to twice as low as those provided by the HPS lamp. Dynamical correction of road luminance against road surface conditions typical of Lithuanian climate was estimated to save about 20% of energy in comparison with constant-level illumination. The estimated energy savings due to the tracking of pedestrians and vehicles amount at least 25% with the cumulative effect of intelligent control of at least 40%. A solid-state street lighting system with intelligent control was demonstrated using a 300 m long test ground consisting of 10 solid-state street luminaires, a meteorological station and microwave motion sensor network operated via power line communication.

Unlike the conventional LED luminary with a planar substrate and only the forward emission, the proposed LED luminary with a curved ceramic substrate can perform both the forward and the backward emissions. Assembled with the proper primary optics, an illustrated LED bulb has been designed, fabricated and measured. The measured luminous intensity of the LED bulb has shown the backward emission and designed distribution with the beam-angle of 133°. To broaden the application areas, such a LED bulb on a curved substrate has been modularized as a streetlight. The measured results of the proposed streetlight have shown that the beam angle of the luminous intensity and the luminaire efficiency are 132° and 86%, respectively. Meanwhile, its luminous characteristics also fit the standard for lighting design of urban roads.asei.c

The characteristics of light-emitting diodes (LEDs) that make them energy-efficient and long-lasting light source for general illumination have attracted a great attention from the lighting industry and commercial market. As everyone know LEDs have the advantages of environmental protection, long lifetime, fast response time (μs), low voltage and good mechanical properties. Their high luminance and the wide region of the dominant wavelengths within the entire visible spectrum mean that people have high anticipations for the applications of LEDs. The output lighting from reflector in the traditional fog lamp was required to fit the standard of the ECE R19 F3 regulation. Therefore, this study investigated the effects of pitch and angle for a diffraction grating in LED fog lamp. The light pattern of fog lamp must be satisfied ECE regulations, so a design of diffraction grating to shift down the lighting was required. There are three LEDs (Cree XLamp XPE LEDs) as the light source in the fog lamp for the illumination efficiency. Then, an optimal simulation of diffraction grating was done for the pitch and angle of the diffraction grating at the test distance of 25 meters. The best pitch and angle was 2mm and 60 degree for the grating shape of wedge type.

Understanding atomic distributions on the order of nanometers is becoming ever more essential to solid-state electronic device design. The local composition of any singular constituent can have a great effect on a host of materials properties. Atom probe tomography is currently the only characterization technique that can provide direct physical detection of ionic species of atoms. In this work, MOCVD grown GaMnN thin films are characterized utilizing the state of the art local electrode atom probe (LEAP^TM) to determine the atomic ordering of Mn in an effort to help understand room-temperature ferromagnetic exchange mechanisms in wide-bandgap dilute magnetic semiconductors. The results support prior magnetometry data that suggest paramagnetism results primarily from isolated Mn atoms. A predisposition for the formation of dimers, trimers or clusters does not exist in the samples grown. The ultimate goal in determining the physical arrangements of atoms and how they related to exchange mechanisms is to understand the structure-propertygrowth condition relationships for the tailoring of specific MOCVD processes that will lead to the ability to selectively control spintronic device functionalities.

In this paper, we propose a self-assembled microlens arrays (MLAs) on top of light emitting diodes (LEDs) based on hydrophilic effect by UV/ozone treatment. After hydrophilic zones were produced by UV/ozone treatment, the substrate with hydrophilic zones was dipped in and out of diluted SU-8 solution with slow and constant velocity. Finally, MLA was formed after UV curing and baking. By this approach, the fabrication is low cost and low time-consuming.

Conventional road lighting luminaries are gradually upgraded by LED luminaries nowadays. It is an urgent problem to design the light distribution of LED luminaries fixed at the former luminaries arrangement position, that are both energysaving and capable of meeting the lighting requirements made by the International Commission on Illumination (CIE). In this paper, a nonlinear optimization approach is proposed for light distribution design of LED road lighting luminaries, in which the average road surface luminance, overall road surface luminance uniformity, longitudinal road surface luminance uniformity, glare and surround ratio specified by CIE are set as constraint conditions to minimize the total luminous flux. The nonlinear problem can be transformed to a linear problem by doing rational equivalent transformation on constraint conditions. A polynomial of cosine function for the illumination distribution on the road is used to make the problem solvable and construct smooth light distribution curves. Taking the C2 class road with five different lighting classes M1 to M5 defined by CIE for example, the most energy-saving light distributions are obtained with the above method. Compared with a sample luminary produced by linear optimization method, the LED luminary with theoretically optimal lighting distribution in the paper can save 40% of the energy at the least.