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The goal of this master thesis is to develop new drive and contrololutions, for creating white light from mixing the light of different-color LEDs, aiming at a reduced component count resulting in less space required by the electronics and lower cost. It evaluates the LED driver concept proposed in the Philips patent application WO2007/125466 and the color accuracy that can be achieved using open loopcontrol (in conjunction with temperature feed forward control).The feasibility of the LED driver concept proposed in WO2007/125466 has been demonstrated, although it has not yet been incorporated into a complete system. Excellent open-loop color control accuracy has been demonstrated for AM and PWM driving and it has been outlined how this can be extended to the new mixed AM/PWM driving proposed inWO2007/125466 (although due to difficulties encountered testing the complete system, its accuracy has not been tested). This would be directly applicable to the temperature feed forward control if the impact of aging on color accuracy would be negligible.

There is a strong interest in using LEDs for general illumination due to the potential they offer for energy saving, environmental friendliness, new opportunities in lighting design, and control of the intensity, colour, and spatial distribution of light. General illumination requires primarily white light that can be obtained by mixinge.g. the light of red, green, and blue LEDs. This enables also colour adjustability, which is considered to be a most attractive featureof future LED lamps [2]. This master thesis takes as a starting pointa previous work done at the Research Group SSL at Philips ResearchLaboratories, Aachen, Germany, by Marc Saura [1]. This previous workwas focused on developing a setup which permits a rapid control proto-typing of a red, green and blue LED-based white light source. Now,using this setup, some improvements and new possibilities have been developed and tested. A brightness control limiting the maximum brightness of the light source has been developed due to the loss of the desired colour of this light source when the LEDs are unable to reachthe requested brightness. This problem can appear both when the userhas set directly an unreachable brightness or due to the effect ofaging on the LEDs. The RGB colour control has been modified in order to add more than three primary colours to the light generation process. An RGBA (Red, Green, Blue, Amber) colour control has been set up adding an amber LED. LED lamps comprising more than three primary colours ex-hibit an increased colour gamut and improved colour rendering index(CRI).

A new method using a thin-film multilayer filter is described to couple light from high-power LEDs into a thin light guide such as an LCD backlight. Light emitted below the critical angle is reflected back to the LED and recycled. Large-angle emitted light passes the filter and is transported by total internal reflection in the light guide. The light guide can be as thin as 0.3mm for an LED of 1x1mm2, and the best coupling efficiency is estimated to be 82%. With this approach, a backlight system can be greatly simplified but also compactcollimators can be realized. In this paper the optical design and testing of the filter is described, and a 1mm thick, 6.5mm diameter collimator is presented. Measurements on prototypes show good agreement with the designed characteristics.

LEDs are strong candidates for future illumination applications dueto their much lower consumption of energy compared to conventional lighting options. One of key problems in development of LEDs is successful thermal management during illumination. Therefore, current research ongoing related to high power LEDs is focusing on improvementof cooling performance of them to enhance light output efficiency, durability and reliability of these devices.The goal of current studyis a first characterization of the LEDs arrays cooling with microchanneled flows. The flow and heat transfer characterization of a 5 LED array on top of water driven microchannels are performed and the junction temperature change with flow rate and thermal resistance isstudied. Experimental results show that the microchannel cooler reduces the junction temperature of LED array and improves the heat dissipation capability of the LEDs themselves.X At very low Reynolds numbers, there are discrepancies found between literature data and ourexperimental results. These discrepancies are explained by uncertainty in general measurements at microscale, including geometrical dimensions and operating parameters. It is demonstrated that the uncertainty in f*Re is dominated by the microchannel width and height measurements. Even a very accurate pressure drop measurements are oftenovershadowed by the geometry measurement uncertainties. In addition,the channel geometry is often not exactly the desired geometry dueto manufacturing difficulties associated withsmall scales. Therefore, the flow behavior is different from the expectations based on theory. Nusselt number variation with Reynolds number is investigated. Nusselt number is almost linearly increasing with Reynolds number inthe low Reynolds number range as also observed in literature. In fact, Nusselt number is expected to be constant in fully developed laminarflow according to the classical laminar flow theory. This does not hold for several reasons such as entrance region effects, unclearboundary conditions in microchannel cross section, multi directional heat transfer, flow configuration as also explained in details previously.

The market of LEDs increases exponentially over the years as well as their power. However, at the same time the mean time to failure should remain superior to 100,000 hours. The major difficulty comes from the mechanical stress in the LED structure, which is roughly proportional to the inverse of the thermal conductivity. Consequently, it is really important to determine thermal conductivity of the materials used in LEDs. In the same way, the thermal conductivity of films is lower than the thermal conductivity of the bulk material. Unfortunately, thermal conductivity measurement is difficult on two-dimensional structures. Then an appropriate method had to be developed. The 3 omega thermal conductivity measurement method has been used extensively to measure the thermal properties of bulk and thin film dielectric materials. Tests on different materials will allow to find materials with a higher thermal conductivity. The thermal conductivity measurement will be elaborated by two different methods defined the isotropic and anisotropic properties, the "slope method" and the 2D heat conduction.

Technological advances in lighting lead towards the development of intelligent LED systems and require reconsidering the way we interactwith lighting systems. In this paper, we report on the workshop ‘User Interaction Techniques for Future Lighting System’ that was heldin conjunction with INTERACT 2011 in Lisbon, Portugal. It was organized to initiate a dialogue between HCI researchers in the lighting domain and establish a research community around this emerging topic,as few researchers systematically study this matter. The goal of the workshop was to formulate the key research challenges for user interaction with future lighting systems. This paper summarizes the workshop paper contributions and the results of a creative session heldduring the workshop. Moreover, we present an initial list of research challenges for this emerging field.

This report summarizes the activities related to the public funded project “Vollintegrierte leistungselektronische Systeme in der Automobilelektronik – VISA” (Fully Integrated Power Electronic Systems in Automotive Electronics). Aim of the project is to investigate the integration of components into printed circuit boards (PCB) for automotive power applications. For Philips, this technology is interesting for integrated LED drivers as used e.g. in automotive head lamps. The project is funded by the German government BMBF under Förderkennzeichen (funding number) 13N9698 and run 3 years from 1.May 2008 until 30.April 2011. It is run by a consortium of the following project partners: Conti Temic microelectronic GmbH (coordinator), Philips Technologie GmbH Forschungslaboratorien, VAC Vacuumschmelze, Schweizer Electronic AG, Chemnitzer Werkstoffmechanik GmbH, Fraunhofer PYCO Teltow, Technische Universität Berlin, RWTH Aachen ISEA and the associate partner Daimler AG. The contributions by Philips Research to the project are to derive a circuit concept and create a demonstrator circuit for an automotive LED headlight driver. Further contributions are the design of integrated magnetic components and the characterization of related soft-magnetic materials. For the LED driver, a resonant converter is selected to minimize switching losses. The demonstrator driver is built as a multilayer PCB with functional layers. It includes winding and soft-magnetic layers for the inductive component and PCB integrated power FETs. The 15W converter has a size of 34 mm x 66 mm with PCB thickness of about 4 mm. It converts an input voltage of 9 V to 18 V to the output of 1 A and about 15 V. The losses are mainly determined by the magnetic component, which are still too high because of the limited properties of the PCB integrated soft-magnetic material. To investigate the properties of soft-magnetic layers, a measurement setup is designed and built, which is used to measure the magnetic permeability of thin layers. 47 samples of Ferrite Polymer Compound (FPC), which were manufactured by the project partner PYCO, are characterized. It was possible to improve the magnetic permeability to μr = 40 and still using PCB compatible polymers. Metallic particles of a material delivered by the partner VAC are used. Furthermore, a measurement setup to measure magnetizing losses is designed and built in cooperation with the partner ISEA. Only the most interesting samples of FPC are characterized. It showed that magnetizing losses could not be improved compared to materials existing before. Concluding, the technology of PCB integration is promising, but the materials needed for a commercial application of this technology need to be developed further.

The design, manufacturing and application of electrowetting-based liquid lenses in optical devices are discussed. Results are presentedof applying this lens in miniature autofocus and zoom cameras, optical recording and illumination systems. Conclusions: We presented the working principle and a concept for mass manufacturing of liquid lenses and we demonstrated that they can be used for focusing and zooming in miniature cameras, for dual-layer readout inBlu-ray Disc optical recording systems and for dynamic effects in illumination systems. This shows that liquid lenses can have a significant impact on future miniature optical devices.

Electronic textiles combine textiles with the functionality of electronic applications.To understand the mechanical issues of reliability, mechanical failure and compatibility of these electronic textiles, research has to be performed that focusses on the interplay of the textile with the electronic components and the conductive wires that feed the components. The aim of this study is to characterize the mechanical behaviour of the textile in combination with the interwoven conductive wires. Furthermore, a lattice model, based on the mesoscale structure of the textile, is proposed to describe this material behaviour. Tensile tests are performed in three directions to obtain the mechanical response of the examined electronic textile. In combination with these tests, tensile tests one single yarns and single conductivewires are performed to obtain their individual mechanical response. The measured responses are mutually compared to gain insight in the influence of the textile's structure on the mechanical response. Moreover, X-ray imaging is performed to examine the failure behaviour of the conductive wires within the textile. A systematic approach is proposed to identify the parameters of the model from the experimental results. The validation of the in-plane lattice model is performed by simulating a three-dimensional punch test in which out-of-plane loading occurs. The mechanical model is evaluated by comparing the experimentally obtained force-displacement curves of the punch with the numerically predicted force-displacement curve.

LumaFluid is an interactive environment that explores new ways to stimulate emotional and social engagement through immersive light effects. A computer vision system detects and tracks persons present inthe LumaFluid square. Using this location information, colored spotlights highlight each person on the installation floor. Connections are also drawn between neighboring visitors, so that dynamic, colorful effects underline and stimulate interpersonal communication. Two versions of the concept where deployed during ten days at the 2011 STRP Art and Technology Festival. In this paper we describe the motivation and the realization of the installation, and we discuss insights and reactions collected during the event.