Wikijunior:How Things Work/Light Bulb
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[edit] Who invented it?
While conversion of electrical energy to light was demonstrated in laboratories as early as 1801 by English scientist Humphry Davy, it took more than 100 years for the modern form of electric light bulb to be developed, with the contributions of many inventors.
The first successful incandescent light bulb was made by the British inventor Sir Joseph Swan in 1860 using a carbon paper filament, but it burned out very quickly.
In 1879, American inventor Thomas Edison created the first incandescent light bulb with the characteristics we recognize today using a carbon filament in an oxygen-free bulb. The first bulbs he experimented with lasted about 40 hours, but he eventually produced a bulb that could produce light for over 1500 hours.
[edit] How does it get power?
Electricity flows through wires to the bulb's socket. This power source may be a battery (as in a flash light) or a distant power plant supplying your local electric utility.
[edit] How does it work?
Electricity flows through a thin wire in the lightbulb called the filament. The filament used in a bulb has a property called "resistance." Resistance is the amount of friction that an object will put against electricity flowing through it. A filament has a lot of resistance to electricity. Therefore as a result of this, the filament heats up and starts glowing, converting electrical energy to light energy. This is because of the Joule-effect, which means that resistances heat up when electrical current runs through them.
[edit] How dangerous is it?
Light bulbs themselves, if used properly, are not dangerous. Although their primary function is to produce light energy, as a side effect they also produce heat.
Light bulbs are sold according to the number of watts they use - the higher the number, the brighter the bulb is, and the more energy it uses. Despite getting hot, lightbulbs don't explode. However, the outer glass of a light bulb which has been on for some time is quite hot, and can cause minor burns, or the broken edges might cut the skin.
After hundreds of hours of operation the filament in the bulb eventually burns out and the light bulb no longer works. The light bulb then needs replacing. It is necessary to be careful in replacing the lightbulb. First, the switch for the light fixture needs to be turned off or the cable disconnected. This is because electricity flowing into the socket where the metallic part of bulb sits can give you a severe electric shock if you touch the inside of the socket or the metal base of the bulb while it is still partly in the socket. In addition, if the glass breaks it is possible to get cuts. These hazards can be reduced by ensuring the bulb is cool to the touch before grasping it and by holding it firmly but not squeezing by the fattest part of the glass while rotating counter-clockwise until it comes completely loose.
[edit] What does it do?
It gives light by converting electrical energy into light energy.
Although we say the filament "burns out" it actually vaporizes over time. Some of it can be seen as darkening on the glass where it has solidified. The gas inside the glass envelope is Argon which is used because it is inert and therefore cannot unite with the filament.
[edit] How does it vary?
The brightness of the filament can be varied by changing the amount of current flowing throught it (the amperage), or the voltage between ends, as the amperage is related to the voltage by Ohm's law. Also, as the filament ages, its brightness will diminish somewhat. Eventually, all filaments will corrode and fail due to the high temperature caused by the electricity flowing through it.
[edit] How has it changed the world?
The lightbulb is probably one of the most significant inventions in science.
It has changed the world by letting people do work at night. Previously this was very hard to do because other light sources (such as candles or fires) did not provide enough light.
The full impact of the lightbulb is much larger than only reading or writing at night.
Travel: Night travel by automobiles has largely been made possible by the lightbulb. Also, light houses all over the world use very powerful light bulbs, and this provides the right guidance for all ships.
Medicine: All internal and non-intrusive medical procedures use variants of the original lightbulb.
Mining: Earlier, underground miners used torches, which also added to the carbon dioxide content in the air, and therefore made breathing difficult. With the advent of lightbulb, mining has also become healthier and safer. In carbon mines, the risk of explosion of the carbon powder contained in the air was so high that conventional fire lanterns couldn't be used (they used a tupid metal mesh covered lanterns), with lightbulbs carbon mining become safer.
Apart from this, the light bulb is used in various other fields including communications, sports, etc.
[edit] What idea(s) and/or inventions had to be developed before it could be created?
Electric Power Generators were needed before light bulbs could be put into people's homes. Replacement for unsafe candles or gas lighting was the initial driver for creating a Power Distribution Network, to put electric wires into the homes of ordinary people. The filament that could 'burn' for many hours had to be developed before people would consider buying a lightbulb.
Initial development focused on electrifying business areas of cities with lighting for the streets and offices. Electric wires of sufficient quality and manufacture had to be invented. The bulb needed to have most of the air evacuated from it to prolong the life of the filament - therefore a vacuum pump. A means to properly insulate the wires, connect the wires to one another and equipment had to be developed to safely distribute the power. Techniques and equipment had to be invented to transmit the power over long distances - hence the development of AC (Alternating Current) and high voltage transmission lines. Fuses, and later circuit breakers had to be developed to avoid damaging the entire line or inaccessible portions thereof. Means to turn on/off lights, motors, and appliances, and move appliances from time to time led to the development of electric switches and outlets.
The electric light bulb was also the genesis for many other inventions based on electricity, including the vacuum tube that led to the transistor used in almost all electronic devices in use today. After people had electricity being delivered to their houses and places of work, inventions such as washing machines, electric irons, motors, radios could take advantage of the convenient source of power available needed to run them. Without the electric light bulb, the world that we live in would be very different.
