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In contrast to classical light bulbs, LEDs used for lighting applications achieve greater energy efficiency. Nevertheless, LEDs are not lossless; power loss generates heat in the semiconductor junctions as well as in the light conversion material. High temperature significantly impairs the luminescent material and results in degeneration of the luminescent encapsulation material whereby its transparency...
LEDs are subjected to environments with high moisture in many applications. In this paper, the experiments reveal photometric and colorimetric degradation at high humidity. Corresponding spectral power analysis and parameter extraction indicate that the flip-chip bonded LED samples show accelerated chip failure compared to the conventionally bonded samples. The chip-related failure induces greater...
A high power LED light-distribution modeling is proposed in this paper. A fitting polynomial of the double Gaussian curve is derived from the illumination measurement of a single LED. The luminance in the lighting area can be balanced by adjusting the lamp current individually according to the optical contour of each LED. From the laboratory experiments, the superposition of the luminance which is...
Highly stress tests were carried out for GaN-based high power white LEDs with different structures, including traditional lateral, vertical as well as flip-chip LEDs. During the tests, all the electrical, optical and thermal properties were measured in-situ for each LED. The results show that for lateral LEDs, the structure property of LED epitaxial layer is still the key factor that influences the...
In this paper, a new control strategy of LED, Constant Luminous Flux Control(CLFC), is proposed, whose foundation is the Photoelectric model of LED. Taking into account the influence of the temperature, Constant Luminous Flux Control can effectively eliminate LED luminous flux decay, which is verified by the theoretical derivation, simulation analysis and experimental study.
In the fast developing LED industry, new generations of LED packages are reaching the market in small time spans. In contrast to that some luminaires, especially in street lighting, should be long lasting and uses the same package over many years. That is one reason why standards are developed to be able to provide lifetime values for the customers. The standard method of calculating the lifetime...
Thermal feature is an important factor of LED. However, as an internal parameter, junction temperature cannot be measured easily. Based on the LED circuit model, which is an ideal diode and a resistor in series, a new model of LED junction temperature Tj is proposed in this paper. Parameters can be extracted from the oil bath experiments. In this way, junction temperature can be derived. The accuracy...
Today, high-power LED packages have been widely used in many fields by virtue of its high efficiency, long service life and small size etc. A LED package consists of many different components, which are made of different materials being operated under different conditions. As a result, each component has its own pattern of impact on the reliability problem of LED packages, such as chip failure, package...
The school dropout is a not negligible phenomenon that, if not effectively contrasted, puts at risk the future of young people and expose them to greater risks of unemployement, poverty and social exclusion compared to peers with a good instruction level. In this paper we present AYO!, an extracurricolar laboratory aimed to contrast the high school dropout. AYO! is an acronym that means Assemble Your...
You may have noticed them going up in your town's streets and parking lots: a new generation of pole-mounted lights that pour down a cool torrent of lumens from an array of light-emitting diodes. Like me, you might have welcomed this development. LEDs are, after all, the most energy-efficient lighting option on the market. They can last twice as long as ordinary sodiumvapor streetlights, and their...
Recently, LED lighting products has attracted much attention due to its cumulative impact on their application field. LEDs are particularly useful in exterior lighting domain because they are excellent directional light sources and reveals long lifetimes. Last generations of white LEDs have higher luminous efficacy and better color rendering than the high intensity discharge lamps. In this paper,...
Silicon photomultipliers (SiPMs), thanks to their excellent performance, are becoming the photodetectors of choice for many applications. One major limitation, in particular for their use at high-luminosity colliders, is the radiation damage by hadrons. In this work, SiPMs with 4384 pixels of 15 × 15 μm2 size produced by KETEK have been irradiated by reactor neutrons to six fluences up to Φeq = 10...
The advent of Integrated Healthcare technology has helped in the development of portable medical devices for measuring vital physiological parameters such as such as Blood glucose and Blood pressure etc. These devices can be afforded by the common man and are readily available in the market. Medical devices of this kind give the firsthand information about the health condition of the patient and also...
Graphene exhibits an extremely high in-plane thermal conductivity, which shows highly prospective value in thermal management and heat spreader application. In this work, graphene sheet was integrated into LED module as intermediate heat spreader with different schemes, and heat dissipation performance was measured and evaluated using standard InfraRed (IR) camera. The experimental data shows that...
Renewable energy exploitation becomes more and more important as consumption type energies are being exhausted. This paper presents the utilization of photovoltaic power applied in LED street lighting and an intelligent street lighting system is developed. The system consists of photovoltaic panels (12V, 60W), a lithium iron phosphate battery(12V, 40Ah), a LED array, a photovoltaic charge controller(CN3722),...
III-nitride semiconductors are well-suited for solid-state lightening, such as light-emitting diodes (LEDs) and laser diodes (LDs). GaN (3.4 eV) alloyed with InN (0.7 eV) and AlN (6.1 eV) can cover a continuous range of a direct band-gap energy. A wide spectrum range from red to deep ultra-violet has been achieved using III-nitride LEDs12. Advanced optoelectronic devices demand higher power output...
The mechanisms of reverse leakage in InGaN/GaN multiple-quantum-wells (MQWs) blue and green light-emitting diodes (LEDs) were studied through analyzing the current–voltage (I–V) characteristics with the temperature ranging from 50 to 350 K. When the reverse bias V is below 12 V, the leakage current is dominated by the variable-range hopping conduction $(T\rm{ < 250\,K)}$ and Poole–Frenkel emission...
This investigation focuses on the influence of the voids on the reliability of solder joints for high-power LED applications. Concerning the long time scale for the reliability tests such as Power cycling tests (PCT), finite-element-method had been considered to enable a simulation-aided analysis and to gain a better understanding of the fatigue behavior of the solder joints with different void distributions...
In recent years, LEDs are widely adopted as a new light source in various applications. Among the many advantages of LEDs over traditional light sources, one key advantage is its long lifespan which substantially reduces the overall maintenance cost. Nevertheless, such characteristic causes various difficulties in the prediction of lifespan and reliability assessment. The lifespan of LEDs can be predicted...
Low power surface-mounted (SMD) LEDs are paid much attention in research and development due to their portability and miniaturization. Optical characteristics of SMD LEDs have to maintain more accurate specifications in signaling applications such as traffic lights or railway. Current and temperature stabilization is important for attaining constant spectral properties of SMD LEDs. In this manuscript,...
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