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Efficiency and Thermal Management of LED Lighting Systems

Unlike two decades ago in the IC world, the junction temperature of an LED is not just a performance indicator of the thermal design but also plays a major role in lighting design since many properties of the light output of an LED depend on the absolute junction temperature. This means that thermal management should be an integral part of the system design of the solid state lightin solution. An important role is played by the printed circuit board whereby LEDs are allocated, main technologies for the realization of the substrates are Insolated Metallic Substrate and High Thermal Conductivity substrate. After learning the main concepts on the thermal management, some electronic systems for the thermal protection were described with also an overview on heat sink types. Purpose of this thesis work is to understand phenomena related to junction temperature that affect LED lighting systems in terms of efficiency and reliability because the most important reason to use thermal data for a LED-based product design is to get an idea about the reliability of the final product, hence, an algorithm based on failure rate (related to junction temperature) for the selection of the number of LEDs were introduced. Also, some important considerations on the kind of vias to employ were discussed.

Mostra/Nascondi contenuto.
Introduction 6 Introduction Light emitting diodes, LEDs, historically have been used for indicators and produced low amounts of heat. The introduction of high brightness LEDs (HB-LEDs) with white light and monochromatic colours has led to a general illumination by means Solid State Lighting (SSL). The luminous efficiency of LEDs is expected to reach over 80 lumens/Watt, about 6 times higher than an incandescent tungsten bulb and thermal management of LEDs is very challenging due to compact size, cost, and long-life. Anyway, SSL is one of the most promising markets in the electronic industry due the possibility for lower power consumption and consequently lower CO 2 emissions. HB-LEDs are opening new market areas where long product life and low power consumption are the key requirements. Typical applications are seen in architectural lighting, street lighting and automotive lighting. Within the SSL design, the lifetime, light-output, efficiency and colour stability are directly linked to the LED-die temperature. LEDs generate a lot of heat; almost 90% of the electrical energy is converted into heat and a rule of thumb in the industry says that every 10°C temperature rise will half the life-time, since a good operation requires at least a life of 50,000 hours it is obvious that this cannot be achieved without taking care of the thermal aspects in lighting design. Purpose of this thesis work is to understand phenomena related to the junction temperature that affect LED lighting systems in terms of efficiency and reliability. In chapter one, how junction temperature affects the LED characteristics will be discussed, focusing on luminous flux (brightness and chromaticity) then a thermal model will be introduced.

Laurea liv.II (specialistica)

Facoltà: Ingegneria

Autore: Giuseppe Pinto Contatta »

Composta da 119 pagine.

 

Questa tesi ha raggiunto 526 click dal 29/01/2010.

 

Consultata integralmente una volta.

Disponibile in PDF, la consultazione è esclusivamente in formato digitale.