High-brightness White Light-emitting Diodes Research Articles

High-performance Al2O3‒YAG:Ce composite ceramic phosphors for miniaturization of high-brightness white light-emitting diodes

The miniaturization of high-brightness white light-emitting diodes (WLEDs) is limited by the low thermal performance of phosphors. In this study, the microstructure, optical properties, and thermal performance of Al2O3–Y3Al5O12:Ce3+ (Al2O3–YAG:Ce) composite ceramics fabricated by hot pressing were investigated. By promoting the growth of Al2O3 grains while maintaining a high composite density, thermal performance of the composite ceramics was significantly increased. The thermal conductivity of a Al2O3–40-vol% YAG:Ce ceramic reached 21.8 W/m/K, which is close to the theoretical value. In addition, this composite ceramic exhibited the highest energy efficiency. After packaging with a high-power LED chip with dimensions of 1 mm × 1 mm, a high luminous flux of 639 lm was generated, while the reduction in output power at 250 °C was as low as 6%. This indicated excellent high-temperature stability and potential for applications in solid-state lighting.

Preparation and optical properties of MgAl2O4-Ce:GdYAG composite ceramic phosphors for white LEDs

High-power light-emitting-diode (LED) lighting has attracted great attention in high-luminance applications. However, the color converters with high stability, high thermal conductivity and high efficiency are scarce. In this work, we developed promising MgAl2O4-Ce:GdYAG composite ceramic color converters in which a broadband yellow-emitting phosphor Ce:GdYAG is combined with a thermally stable spinel phase MgAl2O4. The microstructure, phase composition, photoluminescence and thermal stability were investigated in detail. After being packaged with blue LED, a high luminous efficacy value of 108.4 lm/W is achieved by the composite ceramic phosphor with the molar ratio (MgAl2O4 to Ce:GdYAG) of 1.0 and the thickness of 0.2 mm, as well as high CRI value of 70 and low CCT value of 4543. The light scattering nature of composite ceramic phosphors makes them an ideal and promising candidate for high-brightness white LEDs.

Transparent Ce:GdYAG ceramic color converters for high-brightness white LEDs and LDs

Transparent Ce:GdYAG ceramic phosphors with different Gd3+ contents were successfully prepared by the solid-state reaction method. The absorption and emission properties were investigated at different temperatures. The highest luminous efficiency of 123.7 lm/W was obtained by Ce:YAG ceramic phosphor with the thickness of 1 mm. The addition of Gd3+ results in red-shift and broadening of the emission band of Ce3+ so that the color rendering index (CRI) increases and the correlated color temperature (CCT) decreases obviously after packaged with blue light-emitting diode (LED). The color coordinates of the Ce:GdYAG ceramic phosphor with 50% Gd3+ content based white light device are located at the theoretical white light point in the CIE-1931 chromaticity diagram. And the various CRI and adjustable CCT of warm white light emitted by this device and the high luminous efficiency make Ce:GdYAG ceramics the most promising candidate for high-brightness white LEDs and laser diodes(LDs) device.

Optimal Design of Life Testing for High-Brightness White LEDs Using the Six Sigma DMAIC Approach

Life testing is an essential reliability assessment procedure to qualify a new product or technology before being released to the market. High-brightness white light-emitting diodes (HBWLEDs) with high efficiency, environmental benefits, and high reliability have attracted increasing interest in the field of lighting systems. However, owing to the long lifetime of LEDs, traditional life testing methods for LEDs, which record only failure time, are time consuming and expensive. Therefore, designing an optimal life testing process for HBWLEDs is desirable for accelerating LED technology innovation and development. This paper applies the Six Sigma define–measure–analyze–improve-control (DMAIC) approach to analyze the restrictions in the traditional life testing for HBWLEDs and optimize the life testing procedure. The goal is to shorten the testing time, reduce the testing operation cost, and maintain accurate reliability estimation. In this work, a general reliability estimation method with degradation data is developed by integrating a recursive unscented Kalman filter approach to estimate HBWLED reliability. The results show that, with the help of a recursive UKF, the accuracy of reliability estimation can be improved compared with the ordinary nonlinear least squares approach. Furthermore, the operation time and cost of LED life testing can be reduced by 57.75% and 71.51%, respectively, compared with traditional life testing.

A Single-Inductor, Multiple-Channel Current-Balancing LED Driver for Display Backlight Applications

A single-inductor boost light-emitting diode (LED) driver that can distribute equal dc currents to multiple channels of LEDs is presented. To ensure uniform brightness in display backlight units, the previous approaches used current regulation elements serially inserted in individual LED channels, which incur power losses. Instead, the proposed LED driver adopts a single-inductor-multiple-output boost converter topology, which keeps the channel currents equal in an open-loop fashion by connecting the current-delivering inductor to each channel for an equal period of time, in a time-division multiplexing manner. Furthermore, the sequence of conduction is continuously permutated in order to reduce possible systematic imbalances among the currents. A prototype LED driver demonstrates the peak power efficiency of 93.0% excluding the field-programmable gate array controller power and maximum current balance error of 2.04% while delivering 12.4 W to three channels of high-brightness white LEDs.

Led Lighting Applications-Present Scenario & Future Issues

To comfort today's severe energy crisis the demand-side management is the only solution today. The demand-side management actually means the most efficient application of electrical loads. This is the drive-force to haunt for energy efficient electrical loads, and to search for an energy efficient light source, idea of using a semi-conductor device as a light source named Light Emitting Diodes (LED) was originated. The acceptability of white LEDs for general purpose illumination increases with the introduction of high brightness white LEDs having better lumen output. This paper describes the techniques which have been adopted to increase the lumen output from a LED. The photometric measurement issues are still very crucial in case of LEDs because of lack of standardizations. This paper also discusses the applications point of view of LEDs, its lumen maintenance, life span and finally the scopes of further research & development of it.

Current Development and Patents on High-Brightness White LED for Illumination

In this paper, we reviewed the current development and patents for the application of high-brightness and high-efficiency white light-emitting diode (LED). The high-efficiency GaN nanostructures, such as disk, pyramid, and rod were grown on LiAlO(2) substrate by plasma-assisted molecular-beam epitaxy, and a model was developed to demonstrate the growth of the GaN nanostructures. Based on the results, the GaN disk p-n junction was designed for the application of high brightness and high efficiency white LED.