LC-T: Install and Maintain Different Lamps

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Question 1 of 5

1. Question
Briefly describe the principle of operation of an incandescent lamp.
- As an incandescent lamps burns at a constant voltage, the filament will gradually deteriorate, causing a slow but continuous reduction in wattage and light output, until the normal end of its life is reached when the filament will break or burn through at its thinnest spot.
- This type of lamp consists of a mercury discharge tube in series with a tungsten filament, and are available in BC, ES or GES cap-type.
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Question 2 of 5

2. Question
Briefly describe the principle of operation of a mercury tungsten lamp
- As an incandescent lamps burns at a constant voltage, the filament will gradually deteriorate, causing a slow but continuous reduction in wattage and light output, until the normal end of its life is reached when the filament will break or burn through at its thinnest spot.
- This type of lamp consists of a mercury discharge tube in series with a tungsten filament, and are available in BC, ES or GES cap-type. Operating voltage is 230 volts, and they are obtainable in 160, 250 and 500 watts. The lamp life is ± 6000 hours. When the lamp is initially switched on it takes approximately one to two minutes to obtain its maximum light output. If the power supply is interrupted at any time, the hot re-ignition time takes five to seven minutes. A minimum of 198 volts is required to strike the lamp and an added advantage is that it will operate, mounted in any position
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Question 3 of 5

3. Question
Briefly describe the principle of operation of a fluorescent lamp and its control gear
- As an incandescent lamps burns at a constant voltage, the filament will gradually deteriorate, causing a slow but continuous reduction in wattage and light output, until the normal end of its life is reached when the filament will break or burn through at its thinnest spot.
- This type of lamp consists of a mercury discharge tube in series with a tungsten filament, and are available in BC, ES or GES cap-type.
- In contrast to the well known filament lamp in which electricity flows from one lead wire to another through the solid tungsten wire, thus heating it to incandescence (glowing with heat), the fluorescent lamp is a glass tube, with a filament-type electrode sealed into each of its ends. The filaments are made of coils of tungsten wire and are coated with a material which has the ability to emit electrons. The inner surface of the tube is coated with a layer of a phosphor. For the fluorescent lamp to produce light, control gear is required. The function of the control gear is to create a momentary high voltage impulse, in order to establish an arc between the electrodes (filaments), and to limit the arc current.
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Question 4 of 5

4. Question
Briefly describe the principle of operation of a mercury vapour lamp and its control gear
- The mercury vapour lamp is a discharge-type lamp and therefore requires control gear to stabilise the current. When voltage is applied to the two main electrodes in the discharge tube, ionisation of the gas takes place and current will flow between the electrodes. This current will continue to increase until it destroys the lamp, unless it is externally controlled by continue to increase until it destroys the lamp, unless it is externally controlled by means of a ballast (choke)
- The high-pressure sodium lamp is also a discharge lamp and therefore requires control gear (ballast) to stabilise and control the current.
- The lamp takes about seven minutes to reach its full brightness and it will re-strike immediately if the power is interrupted
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Question 5 of 5

5. Question
Briefly describe the principle of operation of a high-pressure sodium lamp and its control gear
- The mercury vapour lamp is a discharge-type lamp and therefore requires control gear to stabilize the current.
- The high-pressure sodium lamp is also a discharge lamp and therefore requires control gear (ballast) to stabilise and control the current. This type of lamp also requires an ignition to strike the lamp. The lamp is available in phosphor-coated and clear bulbs High-pressure sodium lamps are started by a high-voltage pulse caused by an igniter which ceases to function once the arc has struck. Full brightness is achieved in about five minutes, and the average re-strike time is thirty seconds.
- Other circuits do exist, but they are only used for special purposes such as those used for photography.
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LC-T: Install and Maintain Different Lamps

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