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Seminar Report ’03
Radio Frequency Light Sources
1. 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.
Dept. of AEI
-1-
MESCE Kuttippuram
Seminar Report ’03
Radio Frequency Light Sources
2. 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.
We will consider different kinds of RF discharges and their
advantages and restrictions for lighting applications.
Dept. of AEI
-2-
MESCE Kuttippuram
Seminar Report ’03
Radio Frequency Light Sources
3. DISCHARGE TYPES
There are three practical ways to energize RF light sources, though
there are more ways to create RF plasma
3.1 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).
(Figure 1)
Dept. of AEI
-3-
MESCE Kuttippuram
Seminar Report ’03
Radio Frequency Light Sources
Due to electron depletion in the sheaths, the sheath
impedance is much larger than the plasma impedance. Therefore, the voltage
applied to the lamp is mainly dropped in the sheaths, and sheath impedance
controls the discharge current of a capacitive RF discharge. A significant dc
voltage is developed in the RF sheaths as a result of RF voltage rectification,
and this leads to an acceleration of the plasma ions into the electrodes (or
wall). This has important consequences that limit the application of the CRFD
for RF lighting. The additional power loss of ion acceleration reduces RF lamp
efficiency.
The CRFD power P is proportional to Vrf.,therefore, to achieve a
significant lamp power; one must use a high RF voltage and/or a high
frequency . To reduce ion sputtering, the RF voltage, Vrf applied to the lamp
electrodes should be lower than 100-200V. Since large RF voltages are
prohibited because of ion sputtering, the practical application of a CRFD for
lighting is limited to low power and/or relatively high frequency operation.
(Figure 2)
Dept. of AEI
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MESCE Kuttippuram
Seminar Report ’03
Radio Frequency Light Sources
Example of a CRFD –based lamp is shown in figure 2. This is an RF
–driven sub miniature (a few millimetres in diameter) fluorescent lamp with a
cold cathode. Increasing its driving frequency from 50kHz in standard
application to 40 MHz results in a significant reduction in power loss at the
electrode sheaths. Sheath power loss decreases with frequency.
3.2 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 for which L.
The utility of an IRFD as a light source is defined by its power
transfer efficiency  =Pp/(Pp+Pc), where Pp and Pc are the power delivered to
the plasma and that dissipated in the inductor. To obtain an RF lamp efficiency
equal to, or better than electroded discharge lamps,  should be no less than
about 90%. Power transfer efficiency depends upon many factors, such as
filling gas, gas pressure, discharge topology and geometry, driving frequency,
and inductor construction. Lamp power also has a significant influence on
power –transfer efficiency. Contrary to capacitive RF discharges, where the
fraction of RF power transferred to the plasma falls with increasing discharge
power, usually increases with power in an IRFD.
Dept. of AEI
-5-
MESCE Kuttippuram
Seminar Report ’03
Radio Frequency Light Sources
Figure 3(RF lamp with closed ferrite core)
Typical example of IRFD realisation is shown in figure 3.the closed
ferrite cores increase the coupling between the coil and plasma, thus enhancing
IRFD efficiency.
3.3 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.
Dept. of AEI
-6-
MESCE Kuttippuram
Seminar Report ’03
Radio Frequency Light Sources
4. 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.
An RF generator (RF ballast) is the essential yet most expensive part
of a modern RF lighting system. Electronic ballasts for driving electroded
fluorescent lamps operate at a few tens of kilohertz. For such frequencies,
ballasts efficiencies is rather high (90-95%), its cost is quite reasonable, and
EEMI levels comply with regulations that are more tolerant of lower
frequencies. With increasing frequency, EMI radiations grows, regulations are
more stringent, ballast efficiency decreases, and ballast cost increases. This is
why there is no hope for microwave RF lamps for general lighting .To the
contrary, decades of development of RF light sources shows a preference for
inductive RF discharge and reduction of RF frequency.
With a limited choice of available frequencies for industrial and
residential applications, the inductively coupled plasma source seems to be the
most practical way to make a commercially viable lamp with alight output of
over 1000 lm.
Dept. of AEI
-7-
MESCE Kuttippuram
Seminar Report ’03
Radio Frequency Light Sources
5. COMMERCIAL RF LIGHT SOURCES
Considering the difficulties created by fluorescent lighting, it should
come as no surprise that researchers have been trying to develop a practical
electrode-less light source for years .The main obstacle to the development of a
commercial RF lamp was the lack of efficient and economical electronic
components to drive the lamp frequencies as high as 60 Hz, the level necessary
to produce visible light more efficiently.
Within the past 10 years, the following RF lamp designs have
achieved varying degrees of commercial use:
MICROWAVE- POWERED SULFUR LAMPS
(Figure 4)
Dept. of AEI
-8-
MESCE Kuttippuram
Seminar Report ’03
Radio Frequency Light Sources
This light source is remotely energised by microwave power source
of about 1.5kW at 2.45GHz generated by a magnetron. 1.5kW magnetron,
similar to those used in microwave ovens, generates power at 2.45GHz and
delivers energy to a quartz glass bulb through a short wave guide (Fig.4).
Filled with argon at a small dose of sulphur, the bulb (about 3cm in diameter)
is rotated for discharge stability within the resonant cavity. Providing about
135,000 lumens, or 95 lm/W, and a life rating of 15,000 hr, the compact
sulphur lamp also features low –infrared and ultraviolet emission and good
colour stability.
SPHERICAL EXTERNAL- COIL INDUCTION LAMP
( Figure 5)
This type of lamps employs a 4.5 –cm diameter fluorescent bulb
driven inductively at 13.56MHz from an RF power supply housed in a base
unit (Fig.5). An induction coil wrapped around the lamp energises the neon gas
Dept. of AEI
-9-
MESCE Kuttippuram
Seminar Report ’03
Radio Frequency Light Sources
and a small quantity of mercury contained with in the lamp .In turn, a screen
cage surrounds the lamp to reduce EMI emissions to an acceptable level. The
system operate at 27 W, and the efficiency is 37 lm/W. Typical applications
would be difficult –to-reach locations, such as a bridge or a room with a high
ceiling.
RE-ENTRANT CAVITY INDUCTION LAMP
(Figure 6)
These lamps are operating at 2.65MHz and are available in three
wattages –55W, 85W,and 165W.all three are shaped standard incandescent
lamps (Fig.6). The 85W model is 11cm in diameter and 18cm long.
An induction coil is wound on a ferrite core with an internal copper
heat conductor connected to the lamp base and located in the centre of the
lamp. A heat conductor removes heat from the re-entrant cavity and the
Dept. of AEI
-10-
MESCE Kuttippuram
Seminar Report ’03
Radio Frequency Light Sources
induction coil. A 40 cm coaxial cable delivers power from the electronic
ballast to the base of the lamp. By separating the two components, the ballast
operates cooler, which extents its life. With its vibration resistance, an
efficiency of over 75 lm/W and a 100,000-hr average rated life, this induction
lamp is particularly useful for applications where regular maintenance of
lighting equipment is difficult .A typical application of 165W induction lamps
would be pole-mounted luminaries for dusk –to-dawn illumination on a
campus.
SELF- BALLASTED RE-ENTRANT CAVITY LAMP
(Figure 7)
Dept. of AEI
-11-
MESCE Kuttippuram
Seminar Report ’03
Radio Frequency Light Sources
This compact fluorescent RF lamp has a reentrant topology and
is integrated with an electronic ballast operating at 2.65 MHz. The lamp power
is 23 W at 48 lm/W, and lamp life is rated up to 15,000 hours. Significant
efforts have been made in this lamp for suppressing magnetic and electric
components of EMI to comply with existing regulations.
LOW- FREQUENCY EXTENTED-COIL INDUCTION LAMP
(Figure 8)
This lamps consist of a 5.4 cm diameter Pyrex glass tube constructed
with a rectangular or stretched –donut shape (Fig.8). Two ferrite coils located
on the shorter sides of the rectangular lamp provide the energy coupling. The
power transfer efficiency of this unit is as high as 98%. For example, the
Dept. of AEI
-12-
MESCE Kuttippuram
Seminar Report ’03
Radio Frequency Light Sources
150W lamp offers 80 lm /W efficiency. The lamps operating frequency of
250kHz minimizes the problems associated with EMI, and the ballast design is
much simpler than an RF system working at 2.65MHz. This induction lamp is
particularly useful for applications on bridges, tunnels, high-mounted street
luminaries, and similar difficult-to-reach locations.
Dept. of AEI
-13-
MESCE Kuttippuram
Seminar Report ’03
Radio Frequency Light Sources
6. ADVANTAGES
 Absence of electrodes.
 Some RF elctrodeless lamps on the market today reach 100,000 hours.
 Maintenance is low.
 Gas pressure is optimized for maximal efficiency in RF lamps.
 It have instant and harmless starting and are more convenient for
dimming
 Efficiency is high.
Dept. of AEI
-14-
MESCE Kuttippuram
Seminar Report ’03
Radio Frequency Light Sources
7. DISADVATAGES
 Cost is higher than fluorescent and incandescent lamps.
 With increasing frequency, efficiency will decrease, so microwave RF
lamps not used for general lighting.
 It is woks efficiently for some particular frequencies, if frequency
changes there are problems with electromagnetic interference (EMI).
Dept. of AEI
-15-
MESCE Kuttippuram
Seminar Report ’03
Radio Frequency Light Sources
8. FUTURE SCOPE
Induction lamps are suitable for a range of installations, including
general lighting within a plant, as well as out door areas. Energy conservation
and environmental concerns will inevitably bring about a new generation of
compact residential RF lamps. Induction lighting is an economical choice for
many plants. While it costs two or three times more than a HID lamp and
ballast system, induction lighting last six times longer. Payback, in
maintenance savings alone, can be as fast as one year for hard-to-reach
applications and two to three years for general ambient lighting.
Dept. of AEI
-16-
MESCE Kuttippuram
Seminar Report ’03
Radio Frequency Light Sources
9. 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.
Dept. of AEI
-17-
MESCE Kuttippuram
Seminar Report ’03
Radio Frequency Light Sources
10. BIBLIOGRAPHY
(1)
Bright idea: Radio frequency Light sources By V.A.GODYAK from
IEEE Industry applications magazine, May/June 2002.
(2)
RF lighting tunes in improved Illumination By Joe Knisley from
www.ecmweb.com.
(3)
Website www.plantservices a good fit.com.
(4)
Website www.ibl:gov.com
(5)
McGraw Hill Encyclopedia for Science and Technology Volume-14.
Dept. of AEI
-18-
MESCE Kuttippuram
Seminar Report ’03
Radio Frequency Light Sources
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.
Dept. of AEI
-19-
MESCE Kuttippuram
Seminar Report ’03
Radio Frequency Light Sources
CONTENTS
1.
Introduction
2.
RF Lighting
3.
Discharge types
 Capacitive RF discharge
 Inductive RF discharge
 Wave-sustained RF discharge
4.
Choice of frequency and discharge type
5.
Commercial RF light sources
6.
Advantages
7.
Disadvantages
8.
Further Scope
9.
Conclusion
10. Bibliography
Dept. of AEI
-20-
MESCE Kuttippuram
Seminar Report ’03
Radio Frequency Light Sources
ACKNOWLEDGEMENT
I extend my sincere gratitude towards Prof . P.Sukumaran Head of
Department for giving us his invaluable knowledge and wonderful technical
guidance
I express my thanks to Mr. Muhammed kutty our group tutor and
also to our staff advisor Ms. Biji Paul for their kind co-operation and
guidance for preparing and presenting this seminar.
I also thank all the other faculty members of AEI department and my
friends for their help and support.
Dept. of AEI
-21-
MESCE Kuttippuram