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A gas discharge lamp consists of a transparent gas discharge enclosure containing a small QUANTITY of gas or vapour at a low pressure and two electrodes PROVIDED for connecting the lamp to the supply mains. When the electrodes ESTABLISH a potential difference, the gas gets ionized. Consequently, an electrical CURRENT flows and a luminous discharge is obtained from the excited atom of gas.

A gas discharge lamp consists of a transparent gas discharge enclosure containing a small quantity of gas or vapour at a low pressure and two electrodes provided for connecting the lamp to the supply mains. When the electrodes establish a potential difference, the gas gets ionized. Consequently, an electrical current flows and a luminous discharge is obtained from the excited atom of gas.

The light efficiency in fluorescent tube light is HIGH because the invisible RADIATION is converted into visible radiation with the action of phosphor COATING INSIDE the tube which reduces the loss light energy.

The light efficiency in fluorescent tube light is high because the invisible radiation is converted into visible radiation with the action of phosphor coating inside the tube which reduces the loss light energy.

Fluorescent lamps are most commonly used due to its FOLLOWING advantages over other light sources :-

• Increased efficiency
• Longer life of lamp
• Gives illumination in a VARIETY of colours
• Gives GLARE or glitter free light
• High lighting intensities are achieved without excessive temperature RISE
• Gives DIFFUSED and shadow light
• Gives more comfortable illumination and
• Through initial cost is more it is economical.

Fluorescent lamps are most commonly used due to its following advantages over other light sources :-

FLUORESCENT TUBE LIGHT.

Fluorescent tube light.

A REVERSING SWITCH is used to REVERSE the CURRENT at intervals to prevent the blackening of the tube at positive end due to migration of the MERCURY from the positive end to the negative end of the tube.

A reversing switch is used to reverse the current at intervals to prevent the blackening of the tube at positive end due to migration of the mercury from the positive end to the negative end of the tube.

As there is no effect of inductance on D.C. SUPPLY an extra variable resistance is connected in SERIES with the CHOKE to increase the effective resistance to absorb the DIFFERENCE between the mains voltage and the CORRECT lamp voltage during running.

As there is no effect of inductance on D.C. supply an extra variable resistance is connected in series with the choke to increase the effective resistance to absorb the difference between the mains voltage and the correct lamp voltage during running.

Yes, the CHOKE is necessary to CREATE the voltage IMPULSE at the time of STARTING.

Yes, the choke is necessary to create the voltage impulse at the time of starting.

To IMPROVE the power factor a condenser is connected across the SUPPLY line. The SIZE of the condenser should be 3.25μF for 40 WATT and 7.5 μF for 80 watt lamps.

To improve the power factor a condenser is connected across the supply line. The size of the condenser should be 3.25μF for 40 watt and 7.5 μF for 80 watt lamps.

A resistance of about 100 ohms is connected in SERIES with the radio SUPPRESSOR condenser to CHECK the condenser surges so as to prevent the starter contacts WELDING together.

A resistance of about 100 ohms is connected in series with the radio suppressor condenser to check the condenser surges so as to prevent the starter contacts welding together.

To suppress the RADIO INTERFERENCE a condenser of about 0.05 μF capacity is CONNECTED in parallel with the STARTER.

To suppress the radio interference a condenser of about 0.05 μF capacity is connected in parallel with the starter.

When the fluorescent tube is switched on almost full supply voltage is applied to the starter. The potential across bimetallic electrodes of the starter causes a small glow discharge at a small current not enough to heat up the tube FILAMENTS. This discharge is enough to heat the bimetallic strips of the starter itself causing them to bend and make contact. As a result, the large current flows through the electrodes their temperature being raised to incandescence and the gas in the immediate neighborhood inside the tube gets ionized. At the same time when the contacts of the starter are closed potential difference across it is REDUCED to zero. After two or THREE seconds glow discharge inside the starter stops and the bimetallic strips cool down which breaks the contacts apart. This sudden break induces a very high voltage in the coke connected in series due to its inertia EFFECT and it is sufficient to initiate the discharge in the main tube LIGHT. When the fluorescent tube is a light, current passes through the tube which offers a very low resistance. The voltage across the tube is about 110 volts and rest of the supply voltage of about 110 volts is dropped in the choke. Due to the low voltage, the starter ceases to glow. Starters are so designed that this potential difference across the lamp in running condition is insufficient to restart the glow discharge in the starter. So the contacts remain open, thus the tube is put in operation.

When the fluorescent tube is switched on almost full supply voltage is applied to the starter. The potential across bimetallic electrodes of the starter causes a small glow discharge at a small current not enough to heat up the tube filaments. This discharge is enough to heat the bimetallic strips of the starter itself causing them to bend and make contact. As a result, the large current flows through the electrodes their temperature being raised to incandescence and the gas in the immediate neighborhood inside the tube gets ionized. At the same time when the contacts of the starter are closed potential difference across it is reduced to zero. After two or three seconds glow discharge inside the starter stops and the bimetallic strips cool down which breaks the contacts apart. This sudden break induces a very high voltage in the coke connected in series due to its inertia effect and it is sufficient to initiate the discharge in the main tube light. When the fluorescent tube is a light, current passes through the tube which offers a very low resistance. The voltage across the tube is about 110 volts and rest of the supply voltage of about 110 volts is dropped in the choke. Due to the low voltage, the starter ceases to glow. Starters are so designed that this potential difference across the lamp in running condition is insufficient to restart the glow discharge in the starter. So the contacts remain open, thus the tube is put in operation.

• 38 cm (15”) for 14 watts
• 46 cm (18”) for 15 W
• 61 cm (2”) for 20 W
• 100 cm (3’- 37/8 “) for 25 W
• 122 cm (4’) for 40 W
• 125 cm (5’)for 65 W and
• 125 cm (5’) for 80 W

0.55 A and 0.37 A for 20 W, 0.65 A and 0.43 A for 40W, 1.00 A and 0.67 A for 65 W & 1.3 A and 0.87 A for 80 W respectively.

0.55 A and 0.37 A for 20 W, 0.65 A and 0.43 A for 40W, 1.00 A and 0.67 A for 65 W & 1.3 A and 0.87 A for 80 W respectively.

Due to the presence of inductive CHOKE the POWER FACTOR of the tube lamp is about 0.50.

Due to the presence of inductive choke the power factor of the tube lamp is about 0.50.

All gas discharge LAMPS operated on a 50 Hz alternating current supply are really flickering off and on 100 times PER second. In normal conditions, the human eye does not notice the fact. But when a moving object like rotating parts of machinery is followed, at the certain speed it may appear to be STATIONARY or moving in series of jerks or rotating slowly than its actual speed. This effect of producing an illusion of reality is known as the stroboscopic effect and this is obviously a possible source of danger in factories, machine shops etc.

In fluorescent tube lighting the stroboscopic effect can be eliminated either by using a three lamp unit in which each lamp is connected to a separate PHASE of a 3 phase, 4 wire supply or by using a two-lamp unit in single phase supply each having its own choke but there is only one condenser connected in series with one of the lamps.

All gas discharge lamps operated on a 50 Hz alternating current supply are really flickering off and on 100 times per second. In normal conditions, the human eye does not notice the fact. But when a moving object like rotating parts of machinery is followed, at the certain speed it may appear to be stationary or moving in series of jerks or rotating slowly than its actual speed. This effect of producing an illusion of reality is known as the stroboscopic effect and this is obviously a possible source of danger in factories, machine shops etc.

In fluorescent tube lighting the stroboscopic effect can be eliminated either by using a three lamp unit in which each lamp is connected to a separate phase of a 3 phase, 4 wire supply or by using a two-lamp unit in single phase supply each having its own choke but there is only one condenser connected in series with one of the lamps.