19-02-2010, 12:03 PM
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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
