The original light bulb was an incandescent light bulb. Although the higher wattage incandescent light bulbs are being replaced by the compact fluorescent light bulb (CFL), the lower wattage incandescent bulbs will be around for many years to come.

The way the incandescent light bulb works is that it has two metal contacts at the bottom of the base where they get their power from. These contacts touch the electrical circuit in the fitting which is powered by the electrical circuit from the main electrical panel.

The electrical charge used to light the bulb travels through it from one contact to the other in a loop. The current travels up a wire to the light bulb filament, which is held in place by the supporting glass mount that is in the bulb's center. It then travels across it, down another wire identical to the first, and on to the other contact.

This filament is the central part of the light bulb. It is made out of tungsten, which is a metal with an extremely high melting point. When the light bulb is switched on, the tungsten filament is heated to approximately 2,500 degrees centigrade.

To prevent the filament from burning out, the glass bulb that contains it does not contain any oxygen. It contains an inert gas either argon or a mixture of argon and nitrogen for all regular bulbs. The more expensive bulbs contain krypton/xenon.

The filament is tremendously long and thin. The standard 60 watt bulb tungsten filament wire is over six inches long, but is less than one-hundredth of an inch in diameter. It's double coiled so it will fit in the small space of the bulb. It is wound up tight to produce a first coil then the coil is re-wound again to make the smaller filament that can be seen inside the bulb.

The electrical charge heats up the filament to produce the light. Basically, the electrons that make up the current slams into the tungsten atoms and causes them to vibrate. The vibration friction produces heat or what is called thermal energy, which is captured and then released by the electrons in the form of photons (light). Most of these are unfortunately in the lower end of the light spectrum known as infrared and are invisible to the human eye. The hotter the filament gets, the higher wavelength visible photons are emitted which we can see, and the brighter the light from the bulb.

Higher wattage bulbs such a 100 watt bulb has longer filaments so they produce more light because they have more atoms to vibrate, and conversely, low watt bulbs have shorter coils so the light is dimmer.

The tungsten filament is under tremendous strain, and won't last forever. As the bulb is used over long periods of time the vibration and white-hot temperatures begin to take their toll. Increasingly the atoms from the coiled filament will shake so much they will start to lose contact with each other and begin splitting away from each other, causing the light bulb to fail or what we refer to as light bulb burn out.

That is how incandescent light bulbs work.

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