Application of Power LEDs

components in lighting applications. The topics covered by the subject belong to four basic categories. The first part discuesses the basic properties of light and light sources to the extent needed to understand the different characteristics of LEDs. The highest emphases is put on the physics and construction issues of LEDs and LED-based applications. The third part of the subject covers different solid-state lighting applications from the point of view of requirements against the LEDs used. Special attention is paid to the thermal issues which influence LED operation the most.

Weekly schedule:

Week 1:         Basic properties of light and human vision. Overview of basic quantities used in lighting (e.g. radiant flux, luminous flux, solid angle, illumination). Overview of different light sources (black body radiators, gas discharge lamps, solid-state light sources (LEDs, OLEDs).

Week 2:         Overview of the operation of LEDs as pn-junctions. Recombination processes. I-V characteristics of LEDs: ideal characteristic, effect of the electrical series resistance. Spectral power distribution of different LED types: color LEDs, phosphor converted white LED.

Week 3:         Different compound material systems used in LEDs. Efficiency and efficacy of LEDs. Device constructions assuring high efficiency/efficacy.

Week 4:         Laboratory testing of LEDs (measurement of light output properties and thermal properties). The latest LED testing standards and technical recommendations (CIE, JEDEC).  Temperature dependence of LED operation. Test based multi-domain modeling of LEDs.

Week 5:         Production (in-line) testing of LEDs, binning. Packaging issues of LEDs, assembly issues; level 1, 2, 3, 4 devices: LED chip, packaged LED chip, packaged LED chip assembled to a substrate, substrate with a packaged LED on a cooling assembly.

Week 6:         LED reliability. Reliability and life-time test of LEDs; end-of-life prediction (LM80 and TM21 standards), major failure modes.

Week 7:                  Construction issues of thermal management solutions for LED applications (heat-sinks, thermal interface materials), Thermal analysis of LED applications on luminaire level, CFD modeling and simulation.  

Week 8:         Retrofit LED bulbs (retrofit applications). Major application areas of LED light sources: automotive, indoor, outdoor, backlight modules, special applications (e.g. museum lighting); special requirements against LEDs imposed by the applications.

Week 9:         LED modules. The Zhaga standard. Introduction to LED based lighting applications at industrial site visit (GE)

Week 10:   Some issues of electrical design for LED applications (e.g. LED drivers, dimming). AC driven LEDs.

Week 11:   Visual comfort of LED based solutions (such as color rendering, color fidelity, glare). Photo-biological effects of LED lighting (effects of blue light).

Week 12:   Organic light emitting devices (OLEDs): overview of operation, device construction, modeling issues, applications

Week 13:   Laboratory visit (introduction of typical test equipment like an integrating sphere, a goniometer or a thermal test equipment).

Week 14: Reserve