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How a Light Bulb Works

written by: Chief Engineer Mohit Sanguri • edited by: Lamar Stonecypher • updated: 5/10/2010

Claimed as one of the important inventions the light bulb has a long and interesting history. In this article, along with answering the question about how a light bulb works, we also discuss the relative merits of the light bulb with its competitors like the LED, CFL, and tube light.

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    History of Light Bulb

    How does a light bulb work? When was the light bulb invented?

    Long before the light bulbs were invented, lamps (lanterns) with animal fat, wax, and vegetable oil were used to illuminate homes and surroundings. In 1800, an English scientist named Sir Humphry Davy made the first electric light using batteries (his self-invention) and a piece of carbon, but his light bulb had a very short life. In 1860, Sir Joseph Swan developed an incandescent light using carbon filament, but it also burnt up quickly due to high electric current.

    Thomas Alva Edison started working on the light bulb. He experimented with thousands of filaments, and in 1879 produced a first commercial incandescent lamp with a very high-resistance filament to increase the life of the light. He used an oxygen-free glass bulb. Oxygen helps to burn the carbon filament fast, but in the oxygen-free bulb, the filament will not burn. It only glows, and hence is derived the name “incandescent" light.

    In 1990, William Coolidge invented the tungsten filament which has a very high melting point and thus an even longer life than the carbon filament.

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    Construction and Working Principle of the light bulb

    The light bulb has a tungsten filament as the light emitting media and is specially manufactured by precision machines to give the correct cross sectional area. The tungsten filament is coiled to give a very high resistance and is encased in a glass envelope. This glass envelope or bulb is filled with a low pressure inert gas such as nitrogen or argon. When electricity passes through the coiled tungsten filament, it becomes hot and glows. The inert gas conducts the heat generated by the filament to the glass bulb from where the heat is radiated into the atmosphere.

    Instead of filling the tubes with inert gas, earlier bulbs used a vacuum to increase the life of the filament. The drawback of that arrangement was that the heat generated by the glowing filament would heat up the contact wires, often damaging the insulation and prematurely ending the life of the bulb.

    Incandescent lights work at various voltages ranging from 1.5 volt to higher voltages, however the optimum voltage as per the rating of the bulb must be applied as higher than rated voltages shorten the life.

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    Light Bulb Construction

    Light Bulb
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    Description of Parts of the Light Bulb

    Diagram showing the major parts of a modern incandescent light bulb.

    1. Glass bulb
    2. Inert gas
    3. Tungsten filament
    4. Contact wire (goes to foot)
    5. Contact wire (goes to base)
    6. Support wires
    7. Glass mount/support
    8. Base contact wire
    9. Screw threads
    10. Insulation
    11. Electrical foot contact
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    Comparison of Incandescent lights with tube lights, CFL, and LED Lights

    Incandescent light bulbs are less efficient as compared with CFL, LED, and tube lights as a part of the energy is wasted into heat.

    An incandescent light bulb adds to the heat load of an air conditioning system unlike the other options.

    Incandescent light bulbs can be used with a dimmer circuit thus allowing to control the intensity of the light during romantic candle light dinners. In case of CFL and tube lights we can switch off some of them to get the same effect.

    Incandescent light bulbs can be used for maintaining the temperature of spaces like in mushroom farming, reptile tanks, etc.

    The incandescent light bulb, however, is an old dependable technology that has been used for ages. Though new greener options like LED and CFL lights are available, it would be some time till they are adopted worldwide as cost is one prohibiting factor.

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    Image Credits

    Light Bulb Construction: http://en.wikipedia.org/wiki/File:Incandescent_light_bulb.svg

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