Why electric bulbs are not filled with air and which gas is present in them?

The electric bulb does not contain a vacuum. Under some pressure, the bulb is filled with either argon or argon mixed with some nitrogen. It was common practice in years past to keep a vacuum inside the bulb to prevent the burning of tungsten filament at temperatures above 2000 degrees Celsius. At such high temperatures, tungsten filament begins to lose its atoms. Or, to put it another way, twisted strands tungsten filament slow ‘evaporating. The accumulated carbon from the burnt tungsten particles that escape onto the bulb’s transparent glass becomes an obstruction to light.

In the end, the bulb may not be able to give off enough light. The tungsten filament may also evaporate over time. Erwin Lang-Moore, a well-known American chemist, invented two ways to solve these problems in 1913. (1) He bent the tungsten filament strands and weaved them into a plait. Previously they were spring-like coils. Plaiting made the tungsten filament stronger. (2) He changed the practice of leaving the bulbs in vacuum to fill them with nitrogen or argon. Argon, an inert gas that doesn’t give rise to chemical reactions, would not impact the functioning of the tungsten filament. The filament would be almost impossible to ‘evaporate’ due to the Argon gas’s pressure.

The two above inventions are what make the present-day electric bulb last approximately 1,000 hours.



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