We see a light bulb with thin shield of glass but if we observe it carefully we will see a filament inside it made up of tungsten. Now let us explore how it works. Electricity is passed through the filament which is very long and thin. For 60 watt bulb the filament must be at least six feet long and moreover its diameter must be less than one-hundredth part of an inch. This lengthy filament is coiled double and wounded again and again to make it fit in a bulb. When electricity is passed through this filament it gets heated and this filament holds the current so that it cannot be easily escaped from it by the phenomenon called resistance. It is heated up to 2500 degree Celsius. A part of heat energy is absorbed by the filament and after that it gives out light. The glass of bulb is filled with argon or nitrogen or both. If the oxygen is not removed then the filament will very easily vaporizes and deposits on the walls of glass.
Tungsten filament is also used in halogen lamp in a small sized quartz envelope. And inside it is the gas from halogen group. In these lamps if the filament vaporizes it combines with the gas atoms and recollects on the filament. So we can say by supplying more heat we can get more light. It is also very hot because the quartz envelope lies very close to filament.
Florescent lamp is filled with tough mercury and argon. With the passing of electric current the energy is taken by gas atoms and they give that in the form of ultra violet light. This light hits with phosphorous coated tube giving out the glowing light. They are not heated up because no metal is vaporized and they last longer as compared to ordinary light bulb.
