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radio frequency light sources full report - [email protected] - 08-17-2017 [attachment=15141] INTRODUCTION RF light sources follow the same principles of converting electrical power into visible radiation as conventional gas discharge lamps. The fundamental difference between RF lamps and conventional lamps is that RF lamps operate without electrodes .the presence of electrodes in conventional florescent and High Intensity Discharge lamps has put many restrictions on lamp design and performance and is a major factor limiting lamp life. Recent progress in semiconductor power switching electronics, which is revolutionizing many factors of the electrical industry, and a better understanding of RF plasma characteristics, making it possible to drive lamps at high frequencies. CHAPTER 1 RF LIGHTING The very first proposal for RF lighting, as well as the first patent on RF lamps, appeared about 100years ago, a half century before the basic principles lighting technology based on gas discharge had been developed. 1.1 DISCHARGE TUBES Discharge Tube is the device in which a gas conducting an electric current emits visible light. It is usually a glass tube from which virtually all the air has been removed (producing a near vacuum), with electrodes at each end. When a high-voltage current is passed between the electrodes, the few remaining gas atoms (or some deliberately introduced ones) ionize and emit coloured light as they conduct the current along the tube. The light originates as electrons change energy levels in the ionized atoms. By coating the inside of the tube with a phosphor, invisible emitted radiation (such as ultraviolet light) can produce visible light; this is the principle of the fluorescent lamp. We will consider different kinds of RF discharges and their advantages and restrictions for lighting applications. CHAPTER 2 DISCHARGE TYPES There are three practical ways to energize RF light sources, though there are more ways to create RF plasma 2.1 CAPACITIVE RF DISCHHARGE Capacitive RF discharge may be energised by RF electrodes placed inside or outside the discharge vessel .The current path in a capacitive RF discharge plasma is closed by displacement currents in the RF electrode sheaths (whether the electrodes are inside or outside the discharge vessel). Capacitive RF discharges operate at gas pressure considerably lower than atmospheric pressure and are exited by an RF electric field E with frequency lower than 1GHz wavelength much larger than the discharge size L,( L) radio frequency light sources full report - spawar - 08-17-2017 [attachment=2353] RADIO FREQUENCY LIGHT SOURCES INTRODUCTION Converting electrical power into visible radiation No electrodes RF PLASMA Collection of uncharged molecules Consists of equal number of positive and negative charges RF LIGHTING RF lamps appeared about 100 years ago DISCHARGE TUBES: Glass tube with electrodes at each end DISCHARGE TYPES CAPACITIVE DISCHARGE: Sheath impedance controls the discharge current of capacitive RF discharge Power P is proportional to wVrf CHOICE OF FREQUENCY AND DISCHARGE TYPE The frequency range between 2.2-3.0MHZ has reduced restrictions on EMI For frequencies at a few tens of kilohertz generator efficiency is rather high MICROWAVE GENERATION: Electrons are emitted from cathode Anode surrounding the cathode attracts the electrons Electrons take circular path SPHERICAL EXTERNAL-COIL INDUCTION LAMP Induction coil wrapped around the lamp Screen cage surrounds the lamp to reduce EMI emissions Operates at 27 W Efficiency is 37lm/w RE-ENTRANT CAVITY INDUCTION LAMP Operating at 2.65 MHZ Available in three wattages-55w,85w and 165w Shaped standard incandescent lamps 100,000 hr average rated life SELF-BALLASTED RE-ENTRANT CAVITY LAMP Lamp power is 23w at 48 lm/w Up to 15,000 hours of rated life LOW-FREQUENCY EXTENDED-COIL INDUCTION LAMP: Consists of pyre x glass tube Operating frequency is 250khz Minimizes problems associated with EMI Ballast design is simpler than RF system at 2.65MHz ADVANTAGES Absence of electrodes Maintenance is low It has instant and harmless starting Efficiency is high Control actions from remote places are easy The lamp luminous can be easily controllable DISADVANTAGES Cost is higher than fluorescent and incandescent lamps With increasing frequency efficiency will decrease If the frequency changes there are more problems with EMI More complex design Maintenance is not much easy FUTURE SCOPE Suitable for general lighting within a plant as well as out door areas Economical choice for many plants CONCLUSION Great opportunity for increased durability, light output and efficiency Removes many of the lamp shape restrictions of conventional electrode discharge lamps |