ELECTRIC LAMPS - PART - 04 - OPERATION OF NEON LAMP OR COLD CATHODE FLUORESCENT LAMP (CCFL)



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ELECTRIC LAMPS - PART - 04 - OPERATION OF NEON LAMP OR COLD CATHODE FLUORESCENT LAMP (CCFL)

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ELECTRIC LAMPS – PART – 04
Detailed notes is available in http://zenmurali.blogspot.in
NEON LAMPS OR COLD CATHODE FLUORESCENT LAMPS [CCFL]
INVENTOR OF NEON GAS
The name neon is derived from the Greek word, neos, meaning new.
Neon was discovered in 1898 by the British chemists Sir William Ramsay and Morris W. Travers in London, England.
Neon is chemically inert and forms no uncharged chemical compounds.
It is a colorless, odorless, inert monatomic gas under standard conditions, with about two-thirds the density of air.
Neon is commercially extracted by the fractional distillation of liquid air and it is considerably more expensive than helium, since air is its only source.

INVENTOR OF NEON LAMP
1917 Daniel McFarlan Moore made his mark on lamp history by inventing the negative glow neon lamp.
He developed small bulbs with two electrodes, neon gas glows immediately around the electrodes.
This is used as indicator lights on many devices.
It is still used in decorative Christmas lights since the red light flickers and dances between electrodes similar to a flame.
A neon lamp (also neon glow lamp) is a miniature low pressure cold cathode (gas –discharge) lamp.
The term "Neon Lamp" is used to describe a CCFL with a tube diameter less than 15 millimeters.

OPERATING PRINCIPLE OF NEON LAMPS
1. A neon lamp is a sealed glass tube filled with neon gas.
2. There are electrical terminals at either end of a neon tube.
3. When the tube is switched off, it contains ordinary atoms of
neon gas (red circles).
4. Rig the terminals up to a high-voltage power supply and
switch on, for pulling the neon atoms apart.
5. Some of the atoms will lose electrons to become positively
charged ions (big blue dots).
6. Being positively charged, these neon ions will tend to move
toward the negative electrical terminal.
7. The electrons the neon atoms lose (small blue dots) are
negatively charged, so they hurtle the opposite way toward
the positive terminal at the other end of the tube.
8. In all this rushing about, atoms, ions, and electrons are
constantly colliding with one another.
9. Those collisions generate a sudden smash of energy that
excites the atoms and ions and makes them give off photons
of red light.
10. So many collisions happen with such rapidity that we get a
constant buzzing of red light from the tube.

COLOURS
1. Clear red – Red opaque - Neon Gas with red phosphor
2. Blues, Greens and Yellow – Phosphor with Argon and
Mercury Gas [Argon starts the arc, warms up, then mercury
gas ionizes, UV light is emitted] UV activates the colored
phosphor.
3. Pinkish white and white – Helium gas in a clear tube, or Hg
vapor with a white phosphor.
4. Orange – Neon Gas with yellow phosphor.
5. Whitish-Green – Krypton
6. Bluish-white – Xenon

THERE ARE TWO TYPES OF CCFL
TYPE – 01 – NEON LAMPS - Neon lamps are used in indicators, night lamps and polarity testers. They are generally of 5 watts.
1. They consist of glass bulb filled with neon gas.
2. They give orange pink light.
3. The electrodes are made of iron or steel and are spaced a
few mm.
4. The lamp efficacy lies 15 – 40 lumen per watt.
5. A series resistor is connected in series to control the
magnitude of current. [Electrical tester]

TYPE– 02 – NEON TUBES – These tubes are not used for lighting purpose, but these are used for advertising purposes as neon-signs and letters.
1. Neon tube with varying lengths are employed for advertising
and decoration purposes.
2. These lamps are called as cold cathode lamps because its
operating temperature is 200 degree centigrade.
3. The tubes are mounted either on a wooden frame or metal
base.
4. The tubes are matched with step-up transformers.
5. The electrodes are made of iron, steel or copper in shape of
round and are housed at the two ends of the tube which is
filled with neon gas and connection between letters are
made by nickel wires.
6. The step up transformer secondary is grounded at the mid-
point for safety.
7. The length of the tube may vary from 2 to 10 metre.
8. They be bent into any desired shape during manufacturing.
9. The diametre of the tube may be of 10, 15, 20 and 30 mm
with current of 25, 35, 60 and 150 milliamps.
10. The voltage required is 500 V to 1000 V per metre of the
tube length.
11. Twice the operating voltage is required for starting.
12. Capacitors are used to improve the P.f. which are placed
on the low voltage side of transformer.
13. The capacity of the transformer should be of 50 to 100 VA.
14. The transformer is made in a special manner with a
magnetic shunt. As the tube warms up, its resistance
decreases and the current increases and an ordinary
transformer cannot serve the above purpose.
15. The average working hours of neon tube is about 10,000
hours.

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