Lightbulb

An incandescent lightbulb

A design of an incandescent lightbulb

A lightbulb (or light bulb, light globe, electric lamp, or just bulb) is a device that produces light from electricity when it is turned on. It can be a part of a bigger lighting device, such as a lamp.

Light bulbs are often used to bring light to a space. They can also be used to show information. For example, many electronic devices have a small bulb that shines to show when the device is on. Cars have signal lights to show which way they are turning.

Before electricity became available in the late 1800s, people used candles and oil lamps for light. Lightbulbs were invented earlier that century, but improvements by Thomas Edison made them practical for use at that time. Some people still use oil and lamps, because they do not have electricity.

Types

There are three basic kinds of light bulbs: incandescent, fluorescent and light-emitting diodes. In some places, the word "lightbulb" only means the incandescent kind.

The incandescent light bulb turns electricity into light by passing the electric current through a thin tungsten wire called a filament. The resistance of the filament heats the bulb up. Eventually the temperature of the filament rises so high that it glows. Incandescent bulbs are filled with a gas, often a noble gas like neon or argon, to help them last longer.

In fluorescent bulbs, the electricity passes through gases. Fluorescent lightbulbs are more efficient, because they use less electricity than incandescent bulbs and also last longer. Fluorescent lightbulbs are often tube-shaped. Electricity passes from the positive end of the tube to the negative end through the gas. When the electrons hits a gas molecule, the molecule gives off a photon. The photons hit the wall of the bulb which is has a layer of substances that glow when hit by photons, making light. Changing the mixture in this layer can change the exact color of the light made by the bulb. (Some mixtures make a pink-white colored light, and others make a blue-white colored light.)

Light-emitting diodes (LEDs) are a semiconductor light source. LEDs are used as indicator lamps in many devices and are also becoming more common in other types of lights. LED bulbs last much longer than either incandescent or fluorescent bulbs.

An LED is made of a chip of semiconducting material doped with impurities to create a p-n junction. Like in any other diode, electric current flows easily from one side (the p-side or anode), to the other (the n-side, or cathode), but not the other way. Charge-carriers (both electrons and holes) flow into the junction from electrodes with different voltages. When an electron meets a hole, it falls into a lower energy level, and releases energy in the form of a photon.

Features

Most lightbulbs fit into a socket. Sometimes they are screwed in, other times they fit in the socket through a bayonet action, where they are pushed and twisted into the socket and held in place by two small pins on the bulb. When they break, they must be replaced carefully. They get very hot when they are turned on, and take some time to cool off. There is a danger of electric shock from touching the socket.

Most lightbulbs are made of glass, which means that they are fragile and break easily. In incandescent lightbulbs, the filament eventually will sublimate and break, and the bulb will stop working. Because of this, lightbulbs may need to be replaced more often than the rest of the device.

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  Fluorescent light bulb

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  Light-emitting diode

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  Large LED light bulb

Other pages

Wikimedia Commons has media related to:

Light bulbs

• Fluorescent lamp
• Compact fluorescent lamp