14-05-2013, 12:33 PM
Radio Frequency Light Sources
[attachment=53853]
ABSTRACT
After years of research and development, radio frequency light sources are just now becoming a mainstream lighting option. 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 is that RF lamps operate without electrodes [anode and cathode].
There are three practical ways to energize RF light sources, though there are more ways to create RF plasmas. These three ways correspond to different types of interaction of electromagnetic fields with the bounded plasma and to different kinds of RF discharges. They are: capacitive, inductive and wave sustained discharges.
The most suitable frequency range is 2.2 - 3.0 MHz [2.65MHz is the standard] for RF lighting devices. An RF generator (RF ballast) is the essential yet most expensive part of a modern RF lighting system.
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.
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.
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.
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,
INDUCTIVE RF DISCHARGE
In an inductive RF discharge, the plasma RF current is closed within the plasma without forming RF sheaths. The electric field that maintains the discharge is induced by an RF current flowing through an induction coil outside or inside the plasma. Inductive RF discharges (IRFD) or inductively coupled plasmas (ICP) operate over a wide range of gas pressure and frequency
WAVE –SUSTAINED DISCHARGES
Wave-sustained RF discharges (WRFD) are maintained by electromagnetic waves that are incident on the plasma surface or propagate along a plasma boundary .the wavelength in a wave-sustained RF discharge is comparable to the plasma size ( L), which implies a relatively high RF driving frequency. Wave discharges are usually maintained by microwave power sources at frequency in the GHz range. However, in some surface wave discharges with a long plasma column working as a slow wave structure, the length of the propagating waves is much shorter than in a vacuum, and the driving frequency may be much smaller (10-100 MHz.). The application of microwaves is advantageous for the excitation of high –pressure HID light sources where relatively high- power density is needed to achieve a near –equilibrium plasma.
CHOICE OF FREQUENCY AND DISCHARGE TYPE
A few frequencies allocated for industrial applications such as 13.56,27.12, and 40.68 MHz in the RF frequency band, and to 2.45GHz in the microwave band, the frequency rage between 2.2 – 3.0 MHz (2.65MHz is standard) has reduced restrictions on EMI and has been specifically allocated for RF lighting devices.
CONCLUSION
It has taken nearly a century from the first ideas and the first RF lamp proposals to make commercially viable RF lamps. The elimination of electrodes opens up great opportunity for increased durability, light output and efficiency, and it removes many of the lamp-shape restrictions of conventional electrode discharge lamps .The initial cost of RF lighting products is the major barrier to the widespread RF lamps, but with further development of the many components of RF lighting technology, the range of applications should increase.
[attachment=53853]
ABSTRACT
After years of research and development, radio frequency light sources are just now becoming a mainstream lighting option. 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 is that RF lamps operate without electrodes [anode and cathode].
There are three practical ways to energize RF light sources, though there are more ways to create RF plasmas. These three ways correspond to different types of interaction of electromagnetic fields with the bounded plasma and to different kinds of RF discharges. They are: capacitive, inductive and wave sustained discharges.
The most suitable frequency range is 2.2 - 3.0 MHz [2.65MHz is the standard] for RF lighting devices. An RF generator (RF ballast) is the essential yet most expensive part of a modern RF lighting system.
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.
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.
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.
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,
INDUCTIVE RF DISCHARGE
In an inductive RF discharge, the plasma RF current is closed within the plasma without forming RF sheaths. The electric field that maintains the discharge is induced by an RF current flowing through an induction coil outside or inside the plasma. Inductive RF discharges (IRFD) or inductively coupled plasmas (ICP) operate over a wide range of gas pressure and frequency
WAVE –SUSTAINED DISCHARGES
Wave-sustained RF discharges (WRFD) are maintained by electromagnetic waves that are incident on the plasma surface or propagate along a plasma boundary .the wavelength in a wave-sustained RF discharge is comparable to the plasma size ( L), which implies a relatively high RF driving frequency. Wave discharges are usually maintained by microwave power sources at frequency in the GHz range. However, in some surface wave discharges with a long plasma column working as a slow wave structure, the length of the propagating waves is much shorter than in a vacuum, and the driving frequency may be much smaller (10-100 MHz.). The application of microwaves is advantageous for the excitation of high –pressure HID light sources where relatively high- power density is needed to achieve a near –equilibrium plasma.
CHOICE OF FREQUENCY AND DISCHARGE TYPE
A few frequencies allocated for industrial applications such as 13.56,27.12, and 40.68 MHz in the RF frequency band, and to 2.45GHz in the microwave band, the frequency rage between 2.2 – 3.0 MHz (2.65MHz is standard) has reduced restrictions on EMI and has been specifically allocated for RF lighting devices.
CONCLUSION
It has taken nearly a century from the first ideas and the first RF lamp proposals to make commercially viable RF lamps. The elimination of electrodes opens up great opportunity for increased durability, light output and efficiency, and it removes many of the lamp-shape restrictions of conventional electrode discharge lamps .The initial cost of RF lighting products is the major barrier to the widespread RF lamps, but with further development of the many components of RF lighting technology, the range of applications should increase.