Cette thèse de doctorat porte sur les fluctuations temporelles du flux lumineux des lampes LED, ce phénomène portant le nom de papilottement (flicker). Le papillotement est habituellement considéré comme une perturbation en raison de son impact négatif sur la santé. Pour les systèmes d'éclairage à base de diodes électroluminescentes (LED), sa définition vient d'être formalisée dans la norme IEEE 1789:2015 et a été décrite pour les appareils alimentés en courant alternatif (CA). Ce papillotement alternatif résulte des interactions entre l'impédance du réseau, l'onde de tension, les courants harmoniques et le convertisseur de courant alternatif en courant continu (CA - CC). L'alimentation en courant continu est généralement obtenue via des convertisseurs à découpage. Par conséquent, les mêmes facteurs perturbateurs sont également présents sur les réseaux à courant continu. Cette thèse résume les diférences entre les propriétés caractéristiques du papillotement sous alimentation en CA et en CC. Il a été montré dans la littérature et aussi dans cette thèse qu'avec les LED, le facteur clé qui affecte le papillotement réside dans la conception du driver de LED - une partie indispensable des systèmes d'éclairage à LED. Cette thèse décrit une méthodologie d'évaluation de la sensibilité au papillotement des lampes LED sous alimentation en CC et analyse la façon dont cette sensibilité se modifie lorsque les drivers de LED sont simplifiés et adaptés à des alimentations CC. La thèse présente un ensemble d'expériences de mesure visant à déterminer la réaction typique du papillotement des lampes LED à la fois sous alimentation CA et CC. D'autres expériences ont été efectuées pour révéler l'impact de l'adaptation du driver à l'alimentation CC (en enlevant le pont redresseur à diodes). On constate que certaines lampes présentent une meilleure résistance au papillotement, tandis que d'autres lampes présentent une moindre résistance. Ces expériences sont accompagnées de simulations de drivers pour les lampes LED visant à reproduire et à expliquer les résultats des mesures. La thèse décrit en outre une expérience de mesure visant à montrer la sévérité typique de la variation de tension dans un réseau CC à basse tension couplé au CA domestique et son impact sur le papillotement. On conclut qu'un tel système est suisamment robuste pour filtrer les perturbations provenant du CA, mais une interaction indésirable entre la lampe et l'alimentation peut se produire. / This dissertation thesis is concerned with temporal fluctuations of the luminous flux of LED lamps, a phenomenon referred to as flicker. Flicker is usually regarded as a disturbance due to its negative impact on human health. For lighting systems based on light emitting diodes (LED), its definition has recently been formalised in norm IEEE 1789-2015 and has been documented on devices supplied with AC voltage. AC flicker results from interactions between network impedance, voltage and current harmonics, and the AC to DC converter. DC supplies are generally obtained by switching converters. Consequently, the same perturbing factors are present on DC networks. The thesis summarises the differences between the characteristic properties of flicker under AC and DC supplies. It has been shown in the literature and also in this thesis that the key factor affecting flicker with LEDs is the design of the LED driver-a necessary part of the LED lighting systems. This thesis describes a methodology for the evaluation of the flicker sensitivity of DC supplied LED lamps and analyses how the sensitivity changes when the LED drivers are simplified and accustomed to DC supply. The thesis presents a set of measurement experiments aimed to determine the typical flicker response of LED lamps both under AC and DC supply. Further experiments were performed to reveal the impact of accustomising the driver to the DC supply (removing the diode rectifier). It was found that some lamps show better flicker immunity while other lamps show worse flicker immunity. These experiments are accompanied by LED driver simulations aiming to reproduce and explain the measurement results. The thesis further describes a measurement experiment aimed to show the typical severity of the voltage fluctuation in a low voltage DC network coupled to AC mains and its impact on the flicker. It is concluded that such a system is robust enough to filter out any perturbations coming from the AC supply, but an undesired interaction between the lamp and the supply may occur.

Photocatalytic treatment has the potential to become a cost effective method of organic contaminant removal from water. Photocatalytic materials are semiconductors that enhance chemical reactions such as the breakdown of organic molecules in the presence of light. One of the most studied photocatalysts for water purification is titanium dioxide (TiO2). Variations in the composition of photocatalysts can affect the outcome of the experiments, the detection of the change in behaviour of the photocatalyst is of significant scientific interest. It requires minimisation of the impact of all other factors affecting the photocatalytic process, such as temperature, light intensity, wavelength and uniformity. Repeatability of the experiments is also affected by these factors. If their impact is not considered and addressed the outcome of multiple seemingly identical experiments with a single sample of the photocatalyst will produce different results. Light is one of the most important factors in a photocatalytic process. The undoped TiO2 has a sharp drop in its light absorbtion characteristics between UV and visible spectral regions. It is theregion of the spectrum where most efficient UV LEDs radiate. As the characteristics of the light produced by LEDs are temperature dependent, heat management is important in achieving light with stable characteristics and prolonged lifetime of the LEDs. One of the contributions of this thesis is a novel method of not only stabilisation of the LED radiation parameters, namely optical output power and wavelength, but also the independent control of these parameters. The importance of LED calibration is also a significant contribution as commercial LEDs have dierent radiation parameters between devices. Possibility of independent control of optical power and wavelength of the LEDs has allowed to demonstrate the importance of radiant flux (total spectral power) over the peak spectral flux (power of a single wavelength component) for TiO2 activation, which is another significant contribution of this work. Uniformity of the produced light is another factor that needs to be addressed when a light source for the photocatalytic experimentation is designed. Non-uniform light distribution in a photocatalytic reactor will result in bright spot formation that will affect the overall performance of the photocatalytic sample. This together with the temperature control of the photocatalyst and the water sample are key issues that need to be addressed for achieving ecient and repeatable experimentation outcomes. Photocatalytic reactors developed from simulation to the working prototypes and tested during the work described in this thesis address the problem of light distribution uniformity. They have been designed to remove as many sources of uncertainty usually present in photocatalytic reactors as possible, such as for example temperature stability of the liquid sample, dierent sizes or of the photocatalytic samples and same volume of the liquid sample. As such, these novel reactors together with LED light sources provide a contribution of having a potential of becoming a photocatalytic experimentation standard for achieving the repeatable and comparable results.

The main purpose of this research project was to implement a combination of computer graphics and processing to generate displays that will aid in the visualization of the colour rendering properties of a range of light sources, including the new generation of high-output LEDs (light emitting diodes) that are becoming widely adopted in general lighting service. The CIE (International Commission on Illumination) has developed a colour appearance model CIECAM02 for use in colour imaging and colour management, and this model is utilized in this work. This thesis describes the design and construction of a computer-based model that can be used as a research tool for the simulation and demonstration of the colour rendering properties of various artificial light sources. It is a comprehensive study of the colour models and measurement procedures currently in use in the lighting industry, as recommended by the CIE. This research project focused on the display of a set of surface colour patches as if they were illuminated by a specific light source, and the simultaneous display of two such sets to demonstrate the surface colour differences arising from the use of the two different light sources. A VIS (virtual imaging system) has been developed to display the colour properties of a series of test colour samples under different light sources. This thesis describes the computer models developed for the representation and display of surface colours in general, and colour rendering in particular. The designed system computes and displays the colour of each sample from a knowledge of the light-source spectrum and the spectral reflectance of each surface. It can simultaneously display the colours resulting from illumination by two different sources. In addition, the system computes the colour appearance differences for two sets of colours using the CIECAM02 colour appearance model. Subjective and objective tests were taken to validate the computed results. The VIS has been designed and implemented. It also has been tested by 21 observers and we believe that it will be a powerful research tool for the lighting industry, especially in relation to colour rendering.

I den här uppsatsen presenteras en mindre intervjustudie om hur elever på Barn och fritidsprogrammet i en medelstor kommun i mellersta Sverige upplever utvecklingssamtalen sedan de själva börjat ansvara och leda dem i så kallade elevledda utvecklingssamtal. Det övergripande syftet med undersökningen är att få mer kunskap om elevernas uppfattning över hur de upplever att själva ansvara för utvecklingssamtalets genomförande och hur detta tillvägagångssätt påverkat deras studiemotivation och studieresultat. I resultatet kan vi även ta del av förslag från eleverna hur samtalen kan förbättras i framtiden. I studien har totalt tolv elever från gymnasiets årskurs 1, 2 och 3 deltagit.  Grupperna som intervjuats har haft en jämn könsfördelning och bestått av både studiemotiverade elever och elever med mindre studiemotivation. Detta för att i största möjliga mån spegla utbildningens målgrupp. Majoriteten av de intervjuade är över 18 år. Resultaten visar att majoriteten av de intervjuade eleverna är väldigt positiva till att själv ansvara för och leda sitt utvecklingssamtal med sina vårdnadshavare. Flertalet av de intervjuade tycker även att de blivit mer medvetna om vad som förväntades av dem i skolan för att uppnå ett visst resultat. Utvecklingssamtalet uppfattas nu även som mer avslappnat där de berörda parterna kan koncentrera sig på att diskutera positiv utveckling och inte problem vilket de upplever att tidigare lärarledda utvecklingssamtal många gånger handlat om. Jag tolkar det som att elevledda utvecklingssamtal är något som kommit för att stanna på våra skolor oavsett stadium, både utifrån de elevintervjuer som jag genomfört och de lärare jag samtalat med. Min tolkning styrks även av de styrdokument som vi arbetar utifrån i svenska skolor och i den litteratur, både svensk och amerikansk, som jag tagit del av när studien genomfördes. / This study presents an analysis from interviews with students at the Barn och fritidsprogrammet (Children/Extra-curricular Activities Programme) in a medium-sized municipality in Sweden. The interviews were aimed at identifying how the students perceive developmental talks in school after the students themselves have begun to be responsible for these talks and also manage how the talks are conducted. This concept for development talks is called Student led Conferences. The main purpose of the study was to acquire information about how the students perceive the fact that they are themselves responsible for how the development talks are conducted and how this new method has influenced their motivation to study and their results. The results also present some proposals from the students on how the talks can be further improved in future. Twelve students from high school years 1, 2 and 3 have participated. The groups of students interviewed have been of mixed gender and both students motivated to study and those not so motivated were included. This was done to reflect the current mix of the target population of students for this particular educational programme. The majority of the students interviewed were more than 18 years of age. The results show that the majority of the students interviewed are very positive to be responsible for the development talks and to be in charge of how these talks are conducted together with their custodians. Most of the students interviewed also think that they have become more aware of what is expected from them in school in order to achieve a specific study result. The development talk is now also perceived as more relaxed where the affected parties can concentrate on discussing positive development rather than discussing problems. Before the introduction of student managed development talks the general perception among students was that these development talks tended to focus on problems to a greater extent. My interpretation of the results of this study is that student led conferences is a concept which will continue to be incorporated into our school programmes. My belief is based on conversations with both students and teachers. Furthermore, also the governing documentation that regulates the work in schools in Sweden and the literature, both Swedish and American, that I utilized for this study support the idea of student led conferences.

Det här examensarbetet, på kandidatnivå, har omfattat 15 Hp och har pågått under tio veckor. Arbetet har utförts vid Högskolan på Gotland och har varit ett samarbete med företaget Stylt Trampoli AB i Göteborg. Projektets mål har varit att skapa en kristallkrona till Stora Hotellet i Umeå. Utgångspunkten har varit att återspegla Stora Hotellet nya inredningskoncept och dess värdeord. Arbetet har omfattat designprocessens faser. Det har inneburit en faktainsamling och analys av det berörda området. Samt en redogörelse av idégeneringsarbetet och realiseringensfasens utveckling. Processen och utfallet presenteras i text och bild i rapporten. Resultatet är en 12,5 meter lång kristallkrona bestående av stora kristaller i akrylplast, hängande i hampa rep från taket på fjärde våningen. Tre ljusrör av LED-belysning är placerade i kristallkronan för att sprida ljuset inifrån och ut. Resultatet uppfyller de krav som varit grunden för projektet. / This report presents the Examination Project in a Bachelor of Industrial Design. The project has been created at the University of Gotland and in collaboration with a company named Stylt Trampoli in Gothenburg. The goal of the project has been to create a cut-glass chandelier to Stora Hotellet in Umeå. The foundation has been to reflect the inertialdesign concept of Stora Hotellet and its keywords. The project has included the phases of the design process. The process contains research of facts, analyses and explanations regarding the creative work and development. The process and the outcome are presented in words and images in the report. The result is a 12.5 meter long cut-glass chandelier containing of large crystals made of acrylic, hanging in hemp ropes from the roof on the 4thfloor. Three light pipes of LED-lights are placed within the cut-glass chandelier to spread the light from the inside and out. The result meets the demands which have been the foundation of the project.

Design, fabrication and characterization of III-Nitride pn junction devices Jae Boum Limb 94 pages Directed by Dr. Russell D. Dupuis This dissertation describes an investigation of three types of III-nitride (AlInGaN) based p-n junction devices that were grown by metalorganic chemical vapor deposition (MOCVD). The three types of devices are Ultra-Violet (UV) avalanche photodiodes (APDs), green light emitting diodes (LEDs), and p-i-n rectifiers. For avalanche photodiodes, a material growth on low-dislocation density GaN substrates, processed with low-damage etching receipes and high quality dielectric passivations, were proposed. Using this technology, GaN APDs with optical gains greater than 3000, and AlGaN APDs showing true avalanche gains have been demonstrated. For green LEDs, the use of InGaN:Mg as the p-layer, rather than employing the conventional GaN:Mg has been proposed. Green LEDs with p-InGaN have shown higher emission intensities and lower diode series resistances compared to LEDs with p-GaN. Using p-InGaN layers, LEDs emitting at green and longer wavelengths have been realized. For p-i-n rectifiers, design, fabrication and characterization of device structures using the conventional mesa-etch configuration, as well as the full-vertical method have been proposed. High breakdown devices with low on-resistances have been achieved. Specific details on device structures, fabrication methods, and characterization results are discussed.

¡@¡@A high efficient packaging technique was proposed for power InGaN light emitting diodes( LEDs ).In this approach , sub-mounts based on Si bench technology were used to provide a fact heat conducting channel between the LEDs and the cases.Two different structures of the Si sub-mounts were used, namely, a conventional Si block and a Si block with a copper-filled V-groove. ¡@¡@The thermal resistance of the two different sub-mounts were measured and compared. For a 45mil power LED biased at 1W, thermal resistance of 12.77¢J/W and 18.79¢J/W were measured for the Si sub-mount and the Si sub-mount with copper-filled V-groove. We believe the better thermal resistance of the sub-mount with copper-filled V-groove is due to high thermal conductivity of the copper.

In recent years, even though the light output of GaN-related LED continues to increase, the brightness is still low compared to conventional lighting systems and it is necessary to further improve the light extraction of LEDs. In this study, we utilize the ZnO nanotip with aqueous solution and flip-chip technique to increase the light extraction of GaN LEDs. Electroluminescence (EL) and angular optical distribution are used to measure the light output intensity of LED. In the results, ZnO nanotip after thermal annealing with N2O ambiance decrease the ZnO defects. Flip-chip LED has higher light intensity ( 1.25 times) than conventional one in vertical emitting area ( at 0 angles). The enhancement of light output is duo to the reduction of light absorption from the metal contact and Fresnel¡¦s transmission losses. Finally, we fabricate a high brightness LED with above light enhancement design. EL intensity of LED is increased about 1.38 times than conventional one. Therefore, we can manufacture a LEDs array with above designs to obtain high light output for future solid-state illumination.

The present study was undertaken to determine the effects of varying light intensities on the morphology and physiology of the soft coral Pachyclavularia violacea. The soft corals P. violacea were treated by LED light and the illumination ranged from 50 to 200 £gmol photon m-2 s-1, i.e. high light (200 £gmol photon m-2 s-1), medium light (140 £gmol photon m-2 s-1), medium-low light (100 £gmol photon m-2 s-1 and low light (50 £gmol photon m-2 s-1). The theca length, the density of zooxanthellae and the concentrations of chlorophyll a and proteins were measured to evaluate the response of P. violacea to different light intensities. A significant longer theca length was found in the group of medium-low light (5¡V 9mm) than the groups of high and low light intensities (1-2mm) (p<0.001). And, the theca length in the groups of medium and medium-low was more close to their source population. Over the 6-month experimental periods, the densities of zooxanthellae in the groups of medium and medium-low were in the range of 1.5 ~3.8 x 105 (N/mg) which were significantly higher than other groups (p<0.01). The concentrations of chlorophyll a in the low light group were 0.5~ 2.0 (ng/mg) during the experimental periods which were significantly higher than other groups (p<0.05). In the fifth and sixth months, the concentrations of chlorophyll a per zooxanthellae in the group of medium-low were in the range of 0.4~5.8 Chl. a ¡Ñ 10-5 (ng/zoox.) which were significantly higher than other groups (p<0.01). The protein content in the group of low light was significantly lower than other groups in the fifth month. And, the protein contents were decreased significantly in all groups in the sixth month. Based on the results, it is concluded that theca length and the density of zooxanthellae were sensitive responses to light adaptation. The light intensity about 100 £gmol photon m-2 s-1 might be an appropriate range to culture the soft coral P. violacea because the theca length in the group was close to its source population.

This thesis mainly presents a LED driver circuit based on single-stage Flyback converter with power factor correction. Power factor correction technique is applied for constant current driver. Accroding to different magnetize inductance current operating mode, two methods are used to improve the drawbacks of Flyback converter which is operated in open loop. Discontinuous conduction mode is controlled by single loop which is called voltage follower control. Continuous conduction mode is controlled by dual loop, that applied to nonlinear carrier control(NLC). Multiplier is usually used to traditional power factor correction, but it is expensive. To reduce the system cost, a multiplier is removed from NLC. The designed circuit is verified by SPICE software and experiments. From simulation and experimental results, it shows the proposed system achieves the goal with high power factor and constant output current.