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The spectrum distribution of light-emitting diodes (LEDs) is a critical issue in adopting LEDs as an attractant in insect-catching apparatuses via phototaxis effects. Numerous research efforts have attempted to configure the LED spectrum in line with the insect-sensitive spectrum under designed test conditions. Although successful methods have achieved a stationary spectrum configuration, it is less effective when applied directly to an LED insecticide lamp due to the time-variant behaviors of insects in complex environments. Therefore, dynamic optimization for spectrum distribution of the LED insecticide lamp in practical fields remains essential to improve energy efficiency and the control quality of insects. In this paper, an online learning and dynamic control method has been proposed, where dead insects are evaluated by a partial discharge waveform and a cost function derived from the lamp’s safety, efficiency, and effectiveness is optimized using a proposed jumping-predication algorithm. Then, a detailed procedure for developing a smart and effective LED insecticide lamp based on photovoltaic power supply is illustrated, and finally the LED insecticide lamp is validated. The suggested methodology and experimental results shed light on controlling insects and pests using an LED insecticide lamp in green agriculture.

Junction temperature is a critical metric for reliability evaluation of light-emitting diodes (LEDs) as light sources for automotive lamps. While numerous researchers have quantified the junction temperature accurately, uncertainty factors including electrical–thermal–mechanical boundary conditions and the die-attach layer (DAL) microstructure in automotive LEDs have not been addressed; the propagation of these variables degrades the precision of the junction temperature quantification. In this paper, a junction temperature uncertainty quantification framework involving finite element modeling, the evolution separation spectrum, and Monte Carlo simulation is introduced to build 3-D stochastic finite element models for automotive LEDs with stochastic DAL microstructures. Evolution of the statistical junction temperature probability for three types of automotive LEDs subjected to electrical–thermal–mechanical loadings is discussed and the failure risk is predicted. The results show that the temperature-mechanical displacement coupling of the DAL plays a major role in the junction temperature with regard to automotive boundary loadings, and the thermal power load is more likely to cause junction temperature deterioration of LED with DALs having voids. The automotive LED failure rate is dependent upon the boundary conditions, the DAL microstructures, and the LED numbers. The failure rate for LED modules with DALs having voids is higher than that for modules with uniform DALs; the failure rate is higher in aged LED modules; the failure risk at the given junction temperature threshold increases with increasing LED numbers in the module; and when operating at lower junction temperatures, the voids in LED DALs may not increase the module failure risk.

The light-emitting diode (LED), a semiconductor optoelectronic device, is increasingly introduced into automotive signaling and lighting applications principally due to its exciting design style and long lifetime. Focusing on automotive contexts, numerous researchers have conducted the thermal optimization concerning structure and material properties in LED automotive lamps to maintain the junction temperature operating within a favorable range. However, these efforts mostly rely on thermal simulations with partly component models and specific boundary conditions, and moreover little temperature tolerance has been given from a whole-lamp-level aspect consisting of the electrical, optical, and mechanical requirements. To qualify the temperature tolerance in the thermal design for LED automotive lamps in in-vehicle environment, in this paper, after a description of the design database, the thermal cost objective function, weighted by the electrical, optical, and mechanical objectives, is defined. Then, the multiphysical 3-D simulation model has been made with whole parts in the LED automotive lamp, calibrated by junction temperatures of the typical modules, and integrated with the built database for a graphic user interface application. Finally the temperature sensitivity analysis based on the integrated platform has been performed to accurately estimate the temperature tolerance of the LED automotive lamp. The suggested methodology and experimental results cast light on balancing between the failure risks and costs in LED automotive lamps in the future cars.

Benefited from the fruitful results of general light-emitting diode (LED) lighting, the LED is utilized in the automotive forward lighting recently, the LED headlamp, due to its ability of improving the efficiency, durability and comfort of the automobile. Both the rough operating environments and rigorous safety standards make the design and verification of the LED headlamp face more challenges than that of the general LED lighting. Although there are some concerns about the status of the LED headlamp, these efforts mostly focused on a single issue, and little knowledge has been established from a system-level aspect. To obtain an up-to-date and systematical summary of the progress of the LED headlamp, in this review, after a description of the fundamentals of the LED headlamp, its design methods are scanned firstly following the categorized components: the LED array module, the heat management, optics control as well as the driver electronics; then, the verifications of the LED headlamp are explored according to the plug-in efficiency, cost, lifetime and reliability; next, the trends of the LED headlamp with the additional function of data transmission and integration of human factors are illustrated; and a conclusion is given finally. The results show that the LED headlamp is a complex electrical–optical–thermal–mechanical system, involved human factors; currently it reaches the state-of-the-art on the efficiency, while the cost is about 350% more than that of the halogen headlamps; additionally, the lifetime and reliability issues, which are closely related with the junction temperature and the moisture diffusion, least understands in human response to LED light as well as immature regulations do challenge the development of LED headlamp. However, the system-level, functional and human factors based solutions cast a light on the future LED headlamp.

The gallium nitride (GaN) based white light emitting diode (LED) luminaire system presents a pathway to enhance efficacy, functionality, and the possibility to cut down pollution from traditional lamps. Much effort has been done to improve its performance/price ratio to penetrate the market, including designing and optimizing the LED package structure. Multichips embedded on the aluminum core printed circuit boards (Al-PCB) architecture is one of the features of the LED package method, along with low thermal resistance, low price, and easier development compared with luminaire systems. However, the thermal resistance of the packaged LED varies with the stochastic parameters of the LED packing process, thus posing challenges in packing cost and reliability. In the present paper, the thermal uniformity of packaging the LED array embedded on Al-PCB technology is explored using the Bayesian probability theory. The stochastic thermal characteristics of Al-PCB are investigated by an active infrared imager, and its thermal time constant matrix-based probability is suggested to estimate uniformity. A package design procedure, involving multi-physical finite element simulation, Al-PCB infrared checking, and probability estimation, is proposed. Finally, a 12 LED array for MR-16 lamp is demonstrated. The results show that the thermal uniformity of Al-PCB plays a significant role in packaging multiple LED embedded on Al-PCB, which can be physically indicated by the thermal time constant matrix-based probability. The suggested package procedure sheds light on solving the cost-related thermal uniformity of the LED array. In addition, a proposal to further reduce cost by replacing Au wire with Ag bonding wire is not deemed to be possible based on scanning electron microscopy structure analysis.

The electrical-thermal characteristics of gallium-nitride- (GaN-) based light-emitting diodes (LED), packaged by chips embedded in board (EIB) technology, were investigated using a multiphysics and multiscale finite element code, COMSOL. Three-dimensional (3D) finite element model for packaging structure has been developed and optimized with forward-voltage-based junction temperatures of a 9-chip EIB sample. The sensitivity analysis of the simulation model has been conducted to estimate the current and temperature distribution changes in EIB LED as the blue LED chip (substrate, indium tin oxide (ITO)), packaging structure (bonding wire and chip numbers), and system condition (injection current) changed. This method proved the reliability of simulated results in advance and useful material parameters. Furthermore, the method suggests that the parameter match on Shockley's equation parameters, Rs, nideal, and Is, is a potential method to reduce the current crowding effect for the EIB LED. Junction temperature decreases by approximately 3 K to 10 K can be achieved by substrate thinning, ITO, and wire bonding. The nonlinear-decreasing characteristics of total thermal resistance that decrease with an increase in chip numbers are likely to improve the thermal performance of EIB LED modules.

In order to reduce the Schottky barrier height and sheet resistance between graphene (Gr) and the p-GaN layers in GaN-based light-emitting diodes (LEDs), conductive transparent thin films with large work function are required to be inserted between Gr and p-GaN layers. In the present work, three kinds of transparent conductive oxide (TCO) zinc oxide (ZnO) films, Al-, Ga-, and In-doped ZnO (AZO, GZO, and IZO), are introduced as a bridge layer between Gr and p-GaN, respectively. The influence of different combinations of Gr/ZnO hybrid transparent conducting layers (TCLs) on the optical and thermal characteristics of the GaN-LED was investigated by the finite element method through COMSOL software. It is found that both the TCL transmittance and the surface temperature of the LED chip reduce with the increase in Gr and ZnO thickness. In order to get the transmittance of the Gr/ZnO hybrid TCL higher than 80%, the appropriate combination of Gr/ZnO compound electrode should be a single layer of Gr with ZnO no thicker than 400 nm (1L Gr/400-nm ZnO), 2L Gr/300-nm ZnO, 3L Gr/200-nm ZnO, or 4L Gr/100-nm ZnO. The LEDs with hybrid TCLs consisting of 1L Gr/300-nm AZO, 2L Gr/300-nm GZO, and 2L Gr/300-nm IZO have good performance, among which the one with 1L Gr/300-nm GZO has the best thermal property. Typically, the temperature of LEDs with 1L Gr/300-nm GZO hybrid TCLs will drop by about 7 K compared with that of the LEDs with a TCL without ZnO film.

The development of high-power light emitting diode (LED) for street lighting is growing continuously owing to its greater energy efficiency, long operating life and light control. Users of street lighting are compelled to adopt this technology over traditional light sources. An alternative solution based on a novel 9LEDM (9-LED module) and adaptive driver is shown. The design of the 9LEDM is derived from the thermal, photometric, power electronics techniques to meet the application of street lighting. The 9LEDM performances with a price less than 1$/Watt (W) and luminous flux higher than 110 Lumens (Lm)/W compared with traditional ones. Furthermore, several restrictions of driving the solid-state lighting loads are overcome by an adaptive street lighting driver with an AC/DC converter of a quasi-resonant operation flyback topology and with Soft Startup, Full ON, Half ON functions by sensing the ambient light and working temperature. Finally, a high performance/cost 50 W pole head as a design example is conducted to illustrate the complete design process, and the results from the demonstration projection with two pole heads of 50 W for a 12 m pole show a luminous intensity range from 38 to 19 lux with a heat sink temperature of 58degC and an energy saving more by 72% compared with conventional street lighting after three months of running.

In order to decrease the Schottky barrier height and sheet resistance between graphene (Gr) and the p-GaN layers in GaN-based light-emitting diodes (LEDs), some transparent thin films with good conductivity and large work function are essential to insert into Gr and p-GaN layers. In this work, the ultra-thin films of four metals (silver (Ag), golden (Au), nickel (Ni), platinum (Pt)) are explored to introduce as a bridge layer into Gr and p-GaN, respectively. The effect of a different combination of Gr/metal transparent conductive layers (TCLs) on the electrical, optical, and thermal characteristics of LED was investigated by the finite element methods. It is found that both the TCLs transmittance and the surface temperature of the LED chip reduces with the increase of the metal thickness, and the transmittance decreases to about 80% with the metal thickness increasing to 2 nm. The surface temperature distribution, operation voltage, and optical output power of the LED chips with different metal/Gr combination were calculated and analyzed. Based on the electrical, optical, and thermal performance of LEDs, it is found that 1.5-nm Ag or Ni or Pt, but 1-nm Au combined with 3 layered (L) Gr is the optimal Gr/metal hybrid transparent and current spreading electrode for ultra-violet (UV) or near-UV LEDs.

The thermal-electrical characteristic of a GaN light-emitting diode (LED) with the hybrid transparent conductive layers (TCLs) of graphene (Gr) and NiOx is investigated by a finite element method. It is indicated that the LED with the compound TCL of 3-layer Gr and 1 nm NiOx has the best thermal-electrical performance from the view point of the maximum temperature and the current density deviation of multiple quantum wells, and the maximum temperature occurs near the n-electrode rather than p-electrode. Furthermore, to depress the current crowding on the LED, the electrode pattern parameters including p- and n-electrode length, p-electrode buried depth and the distance of n-electrode to active area are optimized. It is found that either increasing p- or n-electrode length and buried depth or decreasing the distance of n-electrode from the active area will decrease the temperature of the LED, while the increase of the n-electrode length has more prominent effect. Typically, when the n-electrode length increases to 0.8 times of the chip size, the temperature of the GaN LED with the 1 nm NiOx/3-layer-Gr hybrid TCLs could drop about 7 K and the current density uniformity could increase by 23.8%, compared to 0.4 times of the chip size. This new finding will be beneficial for improvement of the thermal-electrical performance of LEDs with various conductive TCLs such as NiOx/Gr or ITO/Gr as current spreading layers.

Finite elements methods are used to investigate the thermal-electrical characteristics of gallium-nitride (GaN) light-emitting diodes (LEDs) with different transparent conductive layers (TCLs) and buried depths of electrodes, where the transparent conductive layers include indium tin oxide (ITO), graphene (Gr) and the combination of them (ITO/Gr). The optimal material parameters and the precision and accuracy of the simulation model are validated. Moreover, the parameters' sensitivity analysis is carried out as well. The results indicate that the LED with the TCL of a 100-nm ITO or 4-layer Gr has a good thermal-electrical performance from the viewpoint of the maximum temperature and the current density deviation of multiple quantum well (MQW), where the maximum temperature occurs at the n-Pad rather than p-Pad. The compound TCL with a 20-nm ITO and 3-layer Gr reaches a thermal-electrical performance better than that of a 100-nm ITO or 4-layer Gr. Moreover, their maximum temperatures decrease about −0.43% and 1.21%, and the current density uniformities increase up to −6.09% and 17.41%, respectively. Furthermore, when the electrode buried depth is 0.51 μm, the thermal-electrical performance of the GaN LEDs can be further improved.

A simple and efficient packaging technique with aluminium-core printed circuit board component embedded copper reflectors is presented for fabricating high-power white light emitting diode (LED) arrays. Three-dimensional finite element simulation and dynamic infrared imaging for analysis of the packaged nine-chips LED array are carried out to investigate the thermal and optical properties. The results show the method, which obtained a luminous efficiency of 126 lm/W and thermal resistance of 3.4 K/W, is suitable for high efficiency and low-cost LED based solid-state lighting.