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The main goal of the present study was to compare the impact of dynamic and static light on work performance and means of different measures of alertness. Ten participants experienced four sessions. Each session had a different lighting: 6000K static light, 9000K static light, CCT- low-frequency dynamic light (cycle = 4 hours, CCT between 6000 and 12000 K) and CCT- high-frequency dynamic light (cycle...
LED light source module is developed according to the design of light distribution of RRGB chip based on the demand of plants for light, temperature and humidity. Several light source modules constitute LED array planar light source module. Monitoring and control of the system is realized through the combination of upper computer based on LabVIEW and controller. The controller conducts real-time detection...
By using a blue light source converted by phosphors to obtain white light emission, phosphor-converted white light emitting diodes (pc-white LEDs) are becoming as one of substitutes of traditional general lighting sources due to their advantages in energy saving, environment-friendliness, color controllability and long lifetime. Within pc-white LEDs, the phosphor films consisting of inorganic phosphor...
We have fabricated three types of high power LEDs with different circuit boards: Al2O3 ceramic board, epoxy PCB with Cu-deposited on the wall of holes and epoxy PCB with Cu-filled through holes. The different contribution of the package have been separated and investigated by using the derivative of temperature rise in the time domain and thermal transient method. The results show that although the...
The COB (Chip-on-Board) arrays are utilized comprehensively, especially in commercial lighting and indoor lighting. Here we would like to discuss the recent progress of COB technology and color quality metrics, including SC5 technology, lumen output, light efficacy, light emitting surface, center beam candlepower, COB performance in SMT LED, correlated color temperature, color consistency, EasyWhite...
A Si-doped GaN films was, grown on 4H-SiC by metal-organic chemical vapor deposition. It was found that the compressively strained layer of the film can be relaxed and surface structural quality can be improved by increasing the thickness of Si-doped GaN film. The critical thickness of beginning of two-dimension growth of GaN on 4H-SiC substrate by metal-organic chemical vapor deposition (MOCVD) has...
We showed a detailed thermal simulation of a high power flip-chip packaged LED, simulation results show that the junction temperature of the LED is more sensitive to the adhesive layer material between the Si substrate and the 1000μm thick Cu heatsink, and less sensitive to the bonding ball material and the heatsink material. Furthermore, three groups of aging tests were conducted on this type of...
In this work, we first proposed an innovation on GaN p-type reflective electrode in flip-chip LEDs (FCLEDs) using a novel method so called electroless silver plating (ESP). In our ESP method, we use chemical way to form a perfect Ag reflector, differ from traditional fabrication of p-type reflective electrode using electron beam deposition (EB). Under our investigation, the Ag reflective electrode...
Smooth and vertical facets for InGaN/GaN double heterostructure lasers grown on sapphire substrate are formed via a two-step method of dry etching and wet chemical etching. This two-step process consists of an inductively coupled plasma (ICP) etching with Ni metal as an etching mask to define the cavity length of the laser bars, followed by crystallographic wet etching in AZ400K developer to reduce...
The drive to increase electrical currents input, and to achieve high lumen output for High Brightness Light Emitting Diode (HB LED) has led to a series of thermal problems. Hence, thermal management is one of key design parameters as the temperature directly affecting the maximum light output, quality, reliability and life time. For LED arrays, the arrangement of chips will affect the thermal performance...
Efficiency droop remains a significant problem to be overcome if the performance of LEDs for solid state lighting is to be improved. As more cost effective substrates such as silicon wafers are used on which to grow the LED active layers, the overall output efficiency and efficiency droop at high drive currents need to be monitored and better understood. This paper investigates the droop effect at...
White light emitting diodes (LEDs) have been regarded as the most promising light sources of new lighting technology due to the properties of high efficiency, energy saving, long lifetime and environmentally friendly. As the key materials used in white LED devices, phosphors strongly influence the properties of the white LED devices, such as luminous efficiency, service life, display color gamut and...
High-power green LEDs in mass-production is reaching a new WPE (wall-plug-efficiency) level of 35%, and this progress results from both band- and strain-engineering in the active multiple-quantum-well region and optimal p- and n-electrodes layout for uniform current spreading. For high-power green LEDs of chip size 45 mil×45 mil (4545 chips), the forward voltage at 350 mA is as low as 2.8 V, with...
Recently, our group has demonstrated several methods to improve the performance of deep ultraviolet (DUV) LEDs and LDs. A high-quality and crack-free AlN template has been achieved by inserting multiple middle-temperature AlN layers with modulated source flow. Using silicon-doped AlGaN MQWs, the internal quantum efficiency (IQE) has been increased by 41% due to the improvement of crystal and interface...
Due to the high Schottky barrier height, traditional AlGaN/GaN SBD always has large turn-on voltage. In this paper, a low turn-on voltage cascode AlGaN/GaN SBD Si realized. A commercial 60 V Si SBD and a high voltage AlGaN/GaN HEMT (>700 V) were used in the design. After co-packaged, the device shows a turn-on voltage with 0.26 V and the breakdown voltage can reach up to 800 V. The reversed recovery...
Mid-power LED in a lead-frame package is the most commonly used LED for LCD backlighting and retrofit LED light source such as light bulb and linear light tube replacement. The lead-frame package consists silver plated copper and white plastic housing, both for the purpose of increasing light reflection. The silver can gradually become darkening when reacting with certain organics gas or chemical...
In the LM 80 testing standard method the lumen maintenance [1] of light sources is measured during their lifetime. As long as the spectral behavior is not changing over time, there is no doubt in that method. Since the integral value of the luminous flux is weighted with the V(λ)-function, degradation in the red and blue parts of the spectrum are represented less than changes in green and yellow spectral...
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