Tungsten Filament lamp give light as a result of heating the filament to a very high temperature. It works on the principle of incandescence. A general term ‘incandescent’ meaning light produced by heat.
There are many types of electric lamps now available in market. They differ by its construction and working principle of operation. The lamps can be grouped on the principle of operation given as follows.
Construction & Working of Tungsten filament lamp:
This lamp consists filament of a fine wire of the metal, tungsten supported in a glass envelope and the air evacuated from the glass bulb – hence this bulb also called as vacuum lamp.
Filaments are constructed by tungsten due to its high melting point property. It operates at a high temperature of 2300o C and has an output of about 8 lm/W (Lumen/watt).
At temperatures above 2000oC, the filament does not melt, but it begins to break up and particles of that filament fly in to the side of the lamp. This causes the glass of bulb to become black. It can frequently observable in torch light bulbs.
The evaporation causes weak spots in the filament resulting in uneven resistance in filament, which sets up hot spots and it burns out and breaks.
Bulb filled with an inert gas like Argon and nitrogen which do not support combustion and they reduce the rate of evaporation.
The operating temperature of an inert gas filled lamp is about 2700oC and output is nearly 12 lm/W.
Figure shows the parts of tungsten filament lamp
Some important points relate to Tungsten filament lamp:
There are two types of filaments are, Single coil filament and Coiled coil filament. The main advantage of a coiled coil lamp is that higher the light output.
General lighting service (GLS) filament lamps used in homes have a bayonet cap (BC) fixed at end of lamp.
The rated life of general lighting service (GLS) lamps is 1000 hours.
The rated life of tungsten filament lamp is achieved in ‘normal conditions of use’.
The normal conditions of use are,
- operated cap up
- Free from vibration
- Voltage not excess the rated voltage.
- Suitable light fittings.
Operating a tungsten filament lamp at a voltage higher than its rated voltage will reduce its life and Lower operating voltage will extend its life.
At higher voltage, the filament lamp gives a whiter and a more bluish light and operates at brighter and higher efficiency.
MCQ Questions PDF for Module 10: Illumination
- Illumination terms – Laws
- Low voltage lamps – different wattage lamps in series
- Various types of Lamps – Carbon arc lamps
- Decorative lamp circuits with drum switches – serial set design – Flasher
- Show case lights and fittings – calculation of lumens efficiency
Download MCQ Questions PDF of Illumination
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