Recently, the high-power light-emitting diodes (LEDs) have been used from the traditional indicator purpose to general illumination purpose. The operating environment and requirement has been more severe. The long operating life high efficiency and high reliability are its main feature attracting the lighting community to this technology. The effect of operating temperature on the degradations of high-power blue LEDs is studied in this thesis. The experiment, measurements, and finite element simulations were conducted to investigate the possible causes of LED degradation. The influence of LED material degeneration on the radiometric pattern was analyzed by tracing rays simulation. Different groups of sample LEDs produced by Lumileds, Unity opto technology Co., and Everlight electronics Co. were studied. Different operating ambient temperatures, e.g. 80oC, 100 oC, and 120 oC, were considered in the accelerated aging test. Experimental results indicated that yellowing, carbonization, gel degeneration, lens chapping and deformation were observed during the test. Results also indicated that the operating temperature is the key factor for LED failure mechanism, that is, different operating ambient temperature may lead to different degradation phenomenon. Numerical simulation results shown that the creep caused by high temperature and thermal stress would cause solder takeoff. This takeoff defects were observed in experimental results. Through ray tracing simulation, it is assured that gel degeneration would change the radiometric pattern of the LED significantly.

Due to the improvement of luminous efficiency, LED has been applied in general lighting nowadays. However, the efficacy and life of high power LED lamps are degraded for the problem of overheat temperature of the chips. In accordance with the above reason, the thermal management has been important in LED application. The thesis aims to analyze the thermal problem of high power LED lamp by FEM. In the beginning, we analyzed the temperature curves and thermal stress curves of chips by changing the thickness of AuSn solder in 4 structures. According to the results, the better thickness range and structures were chosen. In the second step, the effect of different sizes of a vapor chamber on the different thermal conductivities of lamp system was discussed. Finally, we orthogonalized all the designed parameters by Taguchi orthogonal array method, and then found the optimal design by comparing the results with the initial analyses. In this study, we proposed a solution to improve the quality characteristics of LED lamp by Taguchi method. So the effect of each control factors on the performance was able to be determined. For different features of demand, the present study is helpful to achieve the ideal design in manufacturing. Key words: FEM, high power LED lamps, Taguchi orthogonal array method

By focusing on the cooling requirement of high power LED, the study aims to explore the spray cooling method and analyze its cooling performance. The ultrasonic micro-nozzle plate made of piezoelectric ceramic material was used in this experiment in order to establish a spray cooling system. The nozzle plate array (3 ¡Ñ 2) was used to carry out a cooling test for 24 LEDs with high power (6 ¡Ñ 4). Three different watts (1 W, 3 W, 5 W) of LED were tested, the total input power was 24W, 72W and 120 W, respectively, and the working medium was DI water. The goal is to understand the variance in performance caused by nozzle plates of different nozzle diameters (dj = 7, 35 £gm) in varied nozzle distances (z = 10, 20, 30, 40, 50 mm). The experiment used thermocouples to measure the slug temperature of LED. By applying thermal resistnace to the LED to calculate its chip temperature, and using micrometer resolution particle image velocimetry (£gPIV) to observe the spray flowfield inside the LED chamber, this study analyzes the influence of flowfield change on cooling performance.

This study aims to explore the use of an ultrasonic micro-nozzle plate, made of piezoelectric ceramic material, as a core material to establish a set of spray cooling system for high power LED. The system uses a single nozzle plate to implement a cooling test for 4 high power LEDs (2 ¡Ñ 2). The total input power was 4 W, 12 W and 20 W, and working medium was DI water. In order to understand the performance variance introduced by utilizing nozzle plates with differing nozzle diameters (dj = 7, 35 £gm) across various nozzle exit to test distance (z = 10, 20, 30, 40, 50 mm). By using micrometer resolution particle image velocimetry (£gPIV) to observe the spray flowfield inside the chamber, and using thermocouples to measure the temperature of LED slug and thermal resistance was used to calculate the LED junction temperature , Tj, for analyzing the influence of flowfield change spread in chamber on its cooling performance. The possibility of an LED spray cooling system is also explored.

Technological developments in the area of high power LED light sources have enabled their utilization in general illumination applications. Along with this advancement comes the need for progressive thermal management strategies in order to ensure device performance and reliability. Minimizing an LED's junction temperature is done by minimizing the total system's thermal resistance. For actively cooled systems, this may essentially be achieved by simultaneously engineering the conduction through the heat sink and creating a well-designed flow pattern over suitable convective surface area. While such systems are routinely used in cooling microelectronics, their use in LED lighting systems encounter additional constraints which must be accounted for in the design of the cooling system. These are typically driven by the size, shape, and building codes involved with the lighting industry, and thus influence the design of drop-in replacement LED fixtures. Employing LED systems for customary down-lighting applications may require shrouded radial fin heat sinks to increase the heat transfer while reducing the space requirement for active cooling. Most lighting is already in some form of housing, and the ability to concurrently optimize these housings for thermal and optical performance could accelerate the widespread implementation of cost-efficient, environmentally-friendly solid-state lighting. In response, this research investigated the use of conical, cylindrical, square, and pyramidal shrouds with pin/radial fin heat sink designs for the thermal management of high power LED sources. Numerical simulations using FLUENT were executed in order to account for details of the air flow, pressure drop, and pumping power, as well as the heat transfer and temperature distributions throughout the system. The LEDs were modeled as a distributed heat source of 25 - 75 W on a central portion of the various heat sinks. Combinations of device junction temperature and pumping power were used to assess the performance of shrouded heat sink designs for their use in air-cooled, down-lighting LED fixtures.

Langmuir Circulation is a common phenomenon driven by wind in oceans and lakes and was first studied by Langmuir in 1927. According to various ocean observations, this kind of phenomenon plays an important role in many phenomena such as the aggregation of bubbles, the distribution of plankton as well as the mixing of spilled oil and sediment in the ocean. To study this, an experimental facility has been developed in the lab which creates a small scale version of Langmuir Circulation. This thesis is about the design and testing of this tank and surrounding aluminum frame, as well as the design and construction of the illumination equipment (the Green Lantern 2.0) needed for Particle Image Velocimetry measurements within the tank. ANSYS will be used to show whether the tank is structurally strong enough to support the fluid. An enhancement is found that prevents a frontward bend of tank wall, which is analyzed by ANSYS to find an optimized construction to minimize tank deformation. Then, the Light-Emitting Diode (LED) and collimating lens selection for the Green Lantern 2.0 will also be shown in this paper. Besides, this thesis also presents preliminary flow measurement data acquired using the illumination equipment (the Green Lantern).

The aim of my master’s thesis is the design of the LED lighting system for breeding and growing purposes as replacement for the classical high-pressure sodium lamps and other sources of light used today. The whole system can be controlled locally by buttons or remotely by web server using Ethernet interface. LEDs are powered by five-channel step-down converter with current feedback. Converters are controlled by pulse width modulation generated by microcontroller.

This project deals with design and implementation of control system, which is used for regulation climate conditions in special grow box. Measured values are displayed on graphic LCD, sent to application in PC or displayed on web server. The project solves software and hardware implementation of measurement system.