General Lighting Applications Research Articles

A Universal Input CrCM Luo Converter With Low-Cost Pilot-Line Dimming Concept for General Purpose LED Lighting Applications

This paper deals with the design and implementation of a Luo converter operating in two different modes with an improved power quality (PQ) and flickerless operation over the universal ac mains for general purpose lighting applications. A cost-effective analog pilot-line dimming concept is incorporated and discussed in detail. The proposed dimming concept offers good PQ, even during dimming, with low cost for the energy efficient lighting solutions. The Bode plot analysis of this proposed Luo converter is presented using state-space analysis to ensure its stability with closed-loop control. The prototype is developed and tested in the laboratory for a 36-W light-emitting diode lamp load with rated current of 700 mA. The measured power factor in case of 30% dimming is 0.97 with total harmonic distortion of 8.7% only. The measured efficiency is 91% at rated ac mains voltage of 230 V.

System in package (SiP) technology: fundamentals, design and applications

PurposeThe purpose of this paper is to demonstrate a novel 3D system-in-package (SiP) approach. This new packaging approach is based on stacked silicon submount technology. As demonstrators, a smart lighting module and a sensor systems were successfully developed by using the fabrication and assembly process described in this paper.Design/methodology/approachThe stacked module consists of multiple layers of silicon submounts which can be designed and fabricated in parallel. The 3D stacking design offers higher silicon efficiency and miniaturized package form factor. This platform consists of silicon submount design and fabrication, module packaging, system assembling and testing and analyzing.FindingsIn this paper, a smart light emitting diode system and sensor system will be described based on stacked silicon submount and 3D SiP technology. The integrated smart lighting module meets the optical requirements of general lighting applications. The developed SiP design is also implemented into the miniaturization of particular matter sensors and gas sensor detection system.Originality/valueSiP has great potential of integrating multiple components into a single compact package, which has potential implementation in intelligent applications.

Turning Weakly Luminescent SnO2 Nanocrystals into Tunable and Efficient Light Emitters by Aliovalent Alloying

We report the synthesis of ternary gallium tin oxide nanocrystals, and demonstrate that their photoluminescence can be tuned through the visible region by changing Ga:Sn ratio. By substitutional doping with Ga3+, the PL intensity of SnO2 nanocrystals is enhanced by nearly 3 orders of magnitude, reaching photoluminescence quantum yield of >40%. Increase in PL intensity is attributed to the formation of donor and acceptor pairs, and the increase in emission energy is discussed in the context of band-gap expansion and stronger Coulomb interaction between charged defect sites. Time-resolved and steady-state photoluminescence spectroscopies reveal that the interaction of extrinsic and native defects is driven by the nature of the dopant ion. By adjusting various reaction conditions, we prepared the nanocrystals with nearly ideal scotopic-to-photopic ratio and a quantum yield of ca. 34%, attesting to the potential of these nanocrystals for general lighting applications. The results of this work provide new insi...

Packaging of InGaN stripe-shaped light-emitting diodes.

We demonstrate the fabrication of InGaN/GaN stripe-shaped light-emitting diodes (LEDs) in flip-chip packaging (FC-LED) and vertically mounted packaging (VM-LED). Compared to conventionally packaged LEDs, these packaging schemes enhance light output and emission divergence in ways favorable for general lighting applications. The FC-LED can sustain efficiency at high current operations due to effective heat sinking, while the VM-LED excels at light extraction efficiency due to the exposure of two large emission surfaces. Together with the properties of low luminous exitance and emission uniformity, the stripe-shaped LEDs are ideal for the assembly of luminaires. An LED light tube comprising a continuous linear array of 10 stripe-shaped LED chips has been assembled. The optical performance of the light tube is compared to another light tube assembled with conventional square-shaped LED chips (with and without external diffuser) by confocal microscopy. It is found that emission uniformity of the stripe-shaped LED tube is significantly improved, with a threefold increase in illumination area, without efficiency loss associated with diffusers.

Using Red-Emitting Ca2Si5N8Eu2+ Phosphor for Improving Color Uniformity and Color Quality Scale of the in-cup Packaging MCW-LEDs

Light emitting diodes (LEDs) are commonly used in general lighting applications due to their rapidly improving efficiency, long-life, compact, low power consumption, and high climate resistance. In this paper, the Red-Emitting Ca2Si5N8Eu2+ Phosphor was investigated like an innovative approach for improvement on the color uniformity and Color Quality Scale (CQS) of 8500 K, 7700K, 7000 K multi-chip white LED lamps (MCW-LEDs) with the in-cup packaging. The influence of the Red-Emitting Ca2Si5N8Eu2+ Phosphor concentration on the color uniformity and the CQS is simulated, analyzed, and investigated with using Mat lab and LightTools software. The research results indicated that the color uniformity and the CQS were crucially affected by the Red-Emitting Ca2Si5N8Eu2+ Phosphor concentration. This paper provided an important recommendation for selecting and developing the phosphor materials for the in-cup packaging MCW-LEDs manufacturing in the near future.

An Auto-Zero-Voltage-Switching Quasi-Resonant LED Driver With GaN FETs and Fully Integrated LED Shunt Protectors

An auto-zero-voltage-switching (ZVS) quasi-resonant LED driver with gallium nitride (GaN) FETs for general lighting applications is presented. The proposed LED driver switches at high frequency to minimize the inductors to microhenry range. ZVS can be automatically achieved with the proposed controller to eliminate switching loss. The GaN FETs enable high-frequency operation and improve the power efficiency. A fully integrated LED shunt protector is proposed to bypass the failed LEDs in series-connected LED strings. The overall lifetime of the LED strings can be improved, and the maintenance cost can be reduced. The characteristics of the ZVS quasi-resonant LED driver with small inductors and the conditions for ZVS are also discussed in detail. The LED driver is fabricated with a 0.35- $\mu \text{m}$ 120-V high-voltage process. It can provide up to 25-W power to the LED with $2 \times 3.3\,\,\mu \text{H}$ inductors and achieves 91.4% peak efficiency and a 0.973 peak power factor from 60-Hz 100- to 120- $\text{V}_{\mathrm {ac}}$ input.

Copper Iodide Based Hybrid Phosphors for Energy‐Efficient General Lighting Technologies

AbstractSolid‐state‐lighting (SSL) is a new lighting technology that is rapidly replacing conventional lighting sources because it is much more energy efficient, longer lasting, and contributes significantly to environmental protection. A main branch of SSL technology is light‐emitting diodes (LEDs), and white‐light LEDs (WLEDs) are in the greatest demand for general lighting and illumination applications. Current WLED devices rely heavily on rare‐earth elements (REEs), which will likely suffer from cost and supply risks and environmental consequences in the near future. Crystalline inorganic–organic hybrid materials based on I–VII binary semiconductors represent a promising material class as REE‐free phosphor alternatives. This article provides a brief overview of recent advancement on this material family, with a focus on the rational design, energy‐efficient and low‐cost synthesis, systematic modification, and optimization of their electronic, optical, and thermal properties. A particular emphasis will be made on our own progress over the past several years in developing four classes of CuI(L) structures with substantially improved performance as energy‐saving lighting phosphors. General strategies for structural design, synthesis, and property optimization of these materials will also be discussed.

LED lighting, ultra-low-power lighting schemes for new lighting applications

In 2018, Solid-State Lighting (SSL) can totally outperform, if properly designed, most of other lighting products used for general lighting applications. This concerns various attributes such as luminous efficacy, life, spectral qualities, dimming potential, and more and more total cost of ownership. SSL can also mimic a large variety of reference light sources from candlelight to sunlight. The absence of international standards concerning LED modules remains the major difficulty for luminaire manufacturers and their clients, since perfectly matching replacement of ever-changing LED modules is not guaranteed over time. But extraordinarily innovative lighting schemes can be developed, bridging the gap between the world of entertainment and the world of general lighting, and leading to new lighting schemes with more powerful emotional content. LED sources, mostly DC driven, also can benefit from progress in photovoltaics and batteries, as well as wireless control to offer integrated solutions. This could radically change the operation of lighting in the next 10 years. En 2018, les dispositifs luminescents solides (SSL) peuvent surpasser, s'ils sont correctement conçus, la plupart des autres systèmes d'éclairage couramment utilisés. Ceci concerne différentes caractéristiques telles que l'efficacité lumineuse, la durée de vie, les qualités spectrales, le potentiel de gradation et, de plus en plus, le coût total de possession. Les SSL peuvent aussi imiter une large variété de sources lumineuses de référence, de la chandelle au soleil. L'absence de standards internationaux concernant les modules LED reste la difficulté majeure pour les fabricants de luminaires et leurs clients, puisque la possibilité de remplacement à l'identique de modules LED qui changent régulièrement n'est pas garantie dans le temps. Mais des schémas d'éclairage extraordinairement innovants peuvent être développés, jetant une passerelle entre le monde des loisirs et celui de l'éclairage généraliste, conduisant à de nouveaux modes d'éclairage avec un contenu émotionnel encore plus puissant. Les sources LED, pour la plupart alimentées en courant continu, peuvent aussi tirer bénéfice des progrès dans les domaines de l'énergie photovoltaïque et des batteries, aussi bien que dans celui du contrôle sans fil pour offrir des solutions intégrées. Cela pourrait changer radicalement la mise en œuvre de l'éclairage dans les dix prochaines années.

OLED Luminaires: Device Arrays with 99.6% Geometric Fill Factor Structured by Femtosecond Laser Ablation.

The plethora of design opportunities renders organic light emitting diodes (OLEDs) ideal luminaires for general lighting applications. Progressing from lab-scale device concepts to large-area applications calls for smart device designs that are scalable and, at the same time, unsusceptible to resistive losses within the electrodes. By employing direct pulsed femtosecond laser structuring, we fabricate OLED luminaires comprising monolithically interconnected OLED arrays. We determine the laser ablation thresholds and the optimized process parameters for all functional layers. The clean laser cuts with precise ablation depths show no detectable damage to adjacent layers or any ridges, hence avoiding unwanted short-cuts or device isolation. All processes are scalable. The 3-fold structuring of the OLED luminaire is confined within 45 μm and hence below the resolution limit of the human eye, yielding a geometric fill factor beyond 99% and therefore a very homogeneous device perception.

Fabrication of Phosphor-Free III-Nitride Nanowire Light-Emitting Diodes on Metal Substrates for Flexible Photonics

In this paper, we report our study on high-performance III-nitride nanowire light-emitting diodes (LEDs) on copper (Cu) substrates via the substrate-transfer process. Nanowire LED structures were first grown on silicon-on-insulator (SOI) substrates by molecular beam epitaxy. Subsequently, the SOI substrate was removed by combining dry- and wet-etching processes. Compared to conventional nanowire LEDs on Si, the nanowire LEDs on Cu exhibit several advantages, including more efficient thermal management and enhanced light-extraction efficiency (LEE) because of the usage of metal reflectors and highly thermally conductive metal substrates. The LED on Cu, therefore, has stronger photoluminescence, electroluminescence intensities, and better current–voltage characteristics compared to the conventional nanowire LED on Si. Our simulation results further confirm the improved device performance of LEDs on Cu, compared to LEDs on Si. The LEE of the nanowire LED on Cu is nine times higher than that of the LED on Si at the same nanowire radius of 60 nm and spacing of 130 nm. Moreover, by engineering the device-active region, we achieved high-brightness phosphor-free LEDs on Cu with highly stable white-light emission and high color-rendering index of ∼95, showing their promising applications in general lighting, flexible displays, and wearable applications.

An AC Input Switching-Converter-Free LED Driver With Low-Frequency-Flicker Reduction

This paper presents a novel switching-converter-free ac–dc light-emitting diode (LED) driver with low-frequency-flicker reduction for general lighting applications. The proposed driving solution can minimize the system size as it enables the monolithic integration of the controller and power transistors while both the bulky off-chip electrolytic capacitors and magnetics are eliminated. Moreover, the driver can effectively reduce the harmful optical flicker at the double-line-frequency by employing a novel quasi-constant power control scheme while maintaining high efficiency and a good power factor (PF). The proposed driver is implemented with a single controller integrated circuit chip, which includes the controller and high-voltage power transistors, and the off-chip diode bridge and valley-fill circuit. The chip is fabricated with a 0.35- $\mu \text{m}$ 120-V high-voltage CMOS process and occupies 1.85 mm2. The driver can provide up to 7.8-W power to the LED and achieves 87.6% peak efficiency and an over 0.925 PF with only 17.3% flicker from a 110-Vac 60-Hz input.

Optical and microstructural properties of InGaN/GaN multiple quantum wells with embedded graphene coating

We investigate the effects of embedded graphene coating on the optical and microstructural properties of ultrathin InGaN/GaN multiple quantum wells (MQWs). The InGaN/GaN MQWs grown on graphene-buffered GaN templates displayed enhanced internal quantum efficiency compared to conventional ones and showed the internal electric field effect-free characteristic, desirable for general lighting applications. These phenomena were attributed to the enhancement of potential fluctuation with increased indium content and negligible piezoelectric polarization in ultrathin InGaN QWs, respectively. It was found that the atomically rough surface of GaN induced by embedded graphene coating efficiently relieved the biaxial compressive strain in the ultrathin InGaN/GaN QWs and enhanced the In incorporation efficiency during the InGaN growth, suggesting the potential use of atomic-thick carbon layer in niche optoelectronic applications.

The Modeling of Two Phosphors in Conversion White-Light LED

Because of the high color rendering property, the two phosphors that convert into white light in a light-emitting diode are essential in the general lighting applications. Predicting the spectrum after two phosphors mix is challenging because of the mutual interaction between the absorption of long wavelength phosphor and the emission of short wavelength phosphor. To efficiently model the target spectrum, this paper provides a systematic method for simulating the concentration and proportion of two phosphors by using empirical equations. The simulated and experimental spectra overlapped effectively. The results show that the maximum differences are about 0.0046 for CIE 1931 color coordinates (x, y), about 59 K for correlated color temperature, and about five for color rendering index, respectively. The results show that this spectral optimization is an effective approach.

Quantifying the Visibility of Periodic Flicker

ABSTRACTThree experiments that measure the visibility of periodic flicker are presented. Temporal light modulations were presented to a large visual field to make the results valid for general lighting applications. In addition, the experiments were designed to control for flicker adaptation. In the first experiment, the sensitivity of human observers to light modulations with a sinusoidal waveform at several temporal frequencies up to 80 Hz was measured. The results showed that the sensitivity to flicker (that is, the inverse of the Michelson contrast) is as high as 500 for frequencies between 10 and 20 Hz, which is more than twice the maximum sensitivity reported in the literature. In the second experiment, the sensitivity to flicker for light modulations with complex waveforms, composed of two or three frequency components, was measured. Sensitivity to flicker was found to be higher than the sum of the sensitivities of the individual frequency components of the complex waveform. Based on these results, we defined the flicker visibility measure (FVM), predicting flicker visibility by a weighted summation of the relative energy of the frequency components of the waveform. In the third experiment, sensitivity to realistic waveforms (that is, waveforms of light emitting diode [LED] light sources available on the market) was measured. The flicker predictions of FVM showed a high correlation with the experimental data, in contrast to some other existing flicker measures, including flicker index and percent flicker, demonstrating the usefulness of the measure to objectively assess the visibility of periodic flicker for lighting applications.

Transient thermal analysis for accelerated reliability testing of LEDs

Reliability of LED light sources is essential for many general and automotive lighting application where exchange of LED modules would be expensive. Reliability testing to predict the life-time of the devices is required. In this paper transient thermal testing is applied and further developed to monitor the structural integrity of the LED modules during accelerated stress testing. The temperature shock test is one important test because thermo-mechanical stress is a dominating root cause for structural failures as delamination in the package or cracking of solder joints between package and board. New flip chip LEDs (WLP-LEDs) are assembled directly on printed circuit boards (PCB). The initial assembly quality is tested using X-Ray, optical inspection and transient thermal analysis (TTA). In combination the methods deliver essential data to ensure initial assembly quality. Afterwards, the LED modules are exposed to temperature shock tests (−40°C to 125°C) and the TTA is performed repeatedly. By TTA the structural integrity is resolved and cracks or delamination can be identified. Failure modes can be separated and the root cause is investigated by support of transient finite element analysis. One test board is measured In-situ during temperature shock testing. Due to differences in thermo-mechanical stress under hot and cold conditions additional information can be obtained.

The effects of temperature and driving current on the key parameters of commercially available, high-power, white LEDs

High-power LEDs with high luminous efficacies, compact sizes, long lifetimes and a wide colour range, are rapidly taking the place of conventional light sources in general lighting applications. But these properties of high-power LEDs are dependent on temperature and driving current. In this study, 24 samples of commercially available, high-power, white LEDs were measurement for their electrical, optical and thermal characteristics as well as their efficiency, luminous flux, luminous efficacy, correlated colour temperature and colour rendering index over six temperature steps at three different driving currents. LED manufacturers' catalogues including such information will allow consistency between the design and application stages of an installation. Also, it will make the technical and economic optimization of luminaires using high-power LEDs easier.

Investigation of Trapezoidal Well for Improving the Light Efficiency in AlGaInP-Based Light-Emitting Diodes.

We investigated high-brightness light emitting diodes appropriate for general lighting applications in terms of their optical behaviors and device performances according to the insertion of the sloped barrier between the well and the barrier and changing the sloped barrier thickness. As the sloped barrier thickness was increased from 0 to 5 nm, radiative recombination efficiency and device performances significantly improved, due to the suppression of carrier overflow by the stronger capture of carriers and the shortening of the carrier lifetime in the active region owing to the built-in quasi-electric field. At a further increase in the sloped barrier thickness to 10 nm, however, the optical and device performances started to degrade because of the loosening of the quantum confinement effect in the active region and due to the saturation of the improvement of the carrier capture by the sloped barrier region.

Paper No P33: Absorption‐Scattering Based High Pitch Cholesteric Liquid Crystal (HP‐CLC): 3‐D Active Shutter and General Lighting Applications

AbstractIn this article, we exploit an absorption‐scattering based high pitch length cholesteric liquid crystal active shutter. Using the two said fundamental optical properties, we have shown the resultant impact on optical transmission (ON & OFF state) is attracting the general lighting applications. Furthermore, the potential to be used as 3‐D active optical shutter has been endorsed.

Large-area, uniform white light LED source on a flexible substrate.

This study demonstrates the flexible white LED structure with high lumen efficiency and uniform optical performance for neutral white and warm white CCT. Flip-chip LEDs were attached on a polyimide substrate with copper strips as electrical and thermal conduction paths. Yellow phosphors are mixed with polydimenthysiloxane (PDMS) to provide mechanical support and flexibility. The light efficiency of this device can reach 120 lm/W and 85% of light output uniformity of the emission area can be achieved. Moreover, the optical simulation is employed to evaluate various designs of this flexible film in order to obtain uniform output. Both the pitch between the individual devices and the thickness of the phosphor film are calculated for optimization purpose. This flexible white LED with high lumen efficiency and good reliability is suitable for the large area fixture in the general lighting applications.

Synthesis of Lu2.94Ce0.06MgAl3SiO12phosphor and its photoluminescent properties

phosphor used for luminescence convert-ing LED is too high to use in warm white LED applica-tion because of lacking red component [2]. The colortemperature of warm white, cool white and daylightwhite area round 3300 K, 4200 K and 6400 K, respec-tively. For general indoor lighting application, “warmer”white light is recommended [3].To meet the requirements for general illuminationlighting, two major modifications have been developed.One is the modification of the YAG : Ce system, includ-ing co-doping rare earths or transition metal ions, whichcan increase red component [4]. The problem is theenhancement of the red component efficiency is notobvious, and almost all bright and thermal stability ofmodification YAG : Ce are obviously declined. The otheris exploring novel red phosphors which are usuallybased on Eu