Choke’s role
RAM POOJAN CHAURASIA
Sultanpur, Uttar Pradesh
Both conventional
fluorescent lamps (usually 4 feet long) and compact fluorescent lamps —
CFLs ( much smaller both in length and diameter of the tube) used in
lighting applications are low pressure mercury vapour discharge lamps.
These
lamps generate light by the process of fluorescence (accomplishing
conversion of invisible ultra-violet, UV to visible light) by electrical
discharge-passage of electricity through gaseous-vapour medium along
the column of the tube.
When electrical
discharge could strike the column of the tube, lot of invisible UV
radiation having wavelength dominantly at 254 nm is generated. This UV
radiation when strikes the white coating inside the tube made of
fluorescent material- phosphors gets converted to visible light with
wavelengths in the region of 400-700 nm through the process of
fluorescence.
The electrical resistance
of the discharge column of the tube increases with dimensions and
decreases with miniaturization of lamp dimensions.
For
a conventional fluorescent lamp, the ballast used is a choke which
essentially a leak transformer (made of bulk coil windings) which
momentarily produces an inductive kick in the form of high voltage
(approximately 1000 volts) so that the electrical discharge could be
struck along the column of the tube. So in a conventional fluorescent
lamp the role of the choke is to initiate the electrical discharge
process.
Once the discharge is struck
it can be sustained through the drop in electrical resistance of the
column. But CFLs, being smaller in dimensions offering much lower
electrical resistance do not require such bulky chokes. Instead the
discharge in CFLs is initiated by much compact electronic circuits
integrated into the CFL holder. Usually these electronic ballasts are
small oscillator circuits producing high frequencies (approximately 10
kilo Hertz) facilitating flicker free quick start of lamp as electrical
discharge strikes faster at such high frequencies.
R. JAGANNATHAN
Luminescence Group
CECRI
Karaikudi, Tamil Nadu
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