Page 329 - Electrician - TT (Volume 1)

ELECTRICIAN - CITS

Fluorescent tube

It is a low pressure mercury vapor lamp. It consists of a glass tube 25 mm in diameter and 0.6 m, 1.2 m and 1.5 m
in length. The tube contains argon gas at low pressure about 2.5 mm of mercury. At the two ends, two electrodes
coated with some electron emissive material are placed.

A choke is connected in series with the tube which act as a blast and provide a high voltage at starting glow in
the tube. During running condition, the same choke absorbs some supply voltage and remain a voltage of 110 V
across the tube. A capacitor is connected to improve the power factor.
Advantages of Fluorescent Tube

1 Voltage fluctuation has very small effect on light output.
2 The luminous efficiency is more as length of rod is more.
3 It gives light close to natural light.
4 Heat radiations are negligible.
Disadvantages of Fluorescent Tube
1 Its brightness is less.

2 Initial cost is more
3 Overall maintenance cost is high.
ARC LAMP
An arc lamp or arc light is a lamp that produces light by an electric arc.

CARBON ARC LAMP
The carbon arc lamp which consist of an arc between carbon electrodes in air, invented by Humphry davy in
1800s. It was widely used for street light and large building lighting until it was superseded by incandescent light.

It continued in use in more specialized applications where high intensity point light was needed, such as search
light and movie projectors.
Two carbon electrodes placed in contact end to end, in which a direct current is flowing and on separating by
about 0.6 mm, apart gives out a luminous arc.
The arc gives path to the flow of current and the separated ends of carbon emits light rays. The major part of the
light is due to the electrodes and only 5% is given out by arc. About 85% light is given out by positive electrode
which has a temperature of 3500-4000 degcel
Only 10% light is emitted by negative electrode nearly at 2500 degcel.

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CITS : Power - Electrician & Wireman - Lesson 54-59