Lightbulb

An incandescent lightbulb

A design of an incandescent lightbulb

A light bulb, or electric light or electric lamp is a device that produces light from electricity. In addition to lighting a dark space, they can be used to show an electronic device is on, to direct traffic, for heat, and many other purposes.

Before electricity became available in the late 1800s, people used candles and oil lamps for light (often from whale oil). Light bulbs were invented earlier that century, but they had problems and were not useful. Improvements by Thomas Edison and Nikola Tesla made them more practical for use at that time. Edison used a better incandescent material, a higher vacuum, and a higher resistance. This made the bulbs brighter and last much longer. Tesla invented fluorescent lightbulbs, which used a more efficient way to make light.

Types

There are several kinds of light bulbs:

• incandescent - the most common lightbulb in the house until about 2005-2010
• gas discharge lamp - a type of lightbulb that includes the fluorescent light. Compact fluorescent lights (or CFLs) are now replacing incandescent lightbulbs in the house
• light-emitting diodes - previously only used for low-power places, they are now able to be used as lightbulbs in the house
• arc lamp

Light bulbs convert electricity into light and heat. Except for heat lamps, the heat is considered waste. A light bulb that produces more light and less heat is more efficient.

Incandescent

The incandescent light bulb turns electricity into light by sending the electric current through a thin wire called a filament. Filament is made up mostly of tungsten, a type of metal. The resistance of the filament heats the bulb up. Eventually the filament gets so hot that it glows, producing light.

The filament needs to be protected from oxygen in the air, so it is inside the bulb, and the air in the bulb is either removed (a vacuum) or more often, replaced with a gas that doesn't affect anything, like neon or argon. Only about 3% of the energy that goes into an incandescent light bulb actually makes light, the rest makes heat.

This is the type of light bulb that Thomas Edison spent so much time on in the 1870s. It was the first light bulb that could be used in houses - it did not cost too much, and it worked well. For the first time, people did not have to burn something (candles, oil lamps, kerosene lamps, etc.) to make light. It was now bright enough that people could read easily at night or do work. It was used to light stores and streets, and people could travel around after dark. This started the common use of electricity in homes and businesses.

Fluorescent light bulbs

This type of light is efficient, it only give off ¼ the amount of heat of an incandescent. They also last longer than incandescent but until recently were much bigger and did not fit into sockets for small overhead lights and lamps like an incandescent could.

A fluorescent bulb is a glass tube usually filled with argon gas and a little bit of mercury. When turned on, the cathode heats up and sends out electrons. These hit the argon gas and the mercury. The argon gas makes a plasma which lets the electrons move around better. When the electrons hit a mercury molecule it puts the molecule into an excited state (stores the energy). The excited state doesn't last very long, and when the energy is released, it lets out a photon. Photons are particles of light, but the photons from mercury are not visible, they are ultraviolet. So there's a phosphor coating on the wall of the bulb. When the photon hits a phosphor molecule, it in turn puts that molecule into an excited state. When this phosphor releases energy, it lets out a photon that we can see, and light is made. Changing the type of phosphor can change the color we see, but usually fluorescent lightbulbs are whiter than incandescent lightbulbs, which are slightly yellow.

LED

(See main article on light-emitting diodes.) An LED is made like electronics, it is a chip of semiconducting material, usually silicon. LED bulbs are more efficient and last much longer than either incandescent or fluorescent bulbs, do not use mercury (which is dangerous). But until recently they were not as bright, and cost more than either incandescent lights or CFL's.

Cautions

Most light bulbs fit into a socket. If the socket is turned on, there is electricity there, even if the bulb is out, so there is danger of electric shock. Most bulbs get very hot when they are turned on, and take some time to cool off. Most light bulbs are made of glass, which means that they can break easily. Fluorescent bulbs contain a small amount of mercury, if they break, be careful to not breathe the mercury vapor. With incandescent light bulbs, the filament will eventually break, and the bulb will need to be replaced.

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  Fluorescent light bulb

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  Light-emitting diode

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  Large LED light bulb

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  Edison Lightbulb Musée des Lettres et Manuscrits

References

• science theater (June 17, 1992). "How does a lightbulb work?". http://www.pa.msu.edu/sciencet/ask_st/061792.html. Retrieved 20 May 2012.

Other pages

• Fluorescent lamp
• Compact fluorescent lamp