The structure of a light bulb is fairly simple. At the base, there are two small metal contacts which are connected to the ends of the electric circuit. These metal contacts are attached to two hard wires. These wires are attached to a fine metal filament. This filament stands in the centre of the bulb, held in place by a glass mount. The filament and all the wires are encased in a glass bulb which is filled with an inert gas, like argon.

When a light bulb is connected to a power supply, the electrical current runs from one metal contact to the other, moving through the filament and all the wires. Electrical current in a solid conductor is measurable by the movement of free electrons (ones that detach themselves from atoms) from an area with a negative charge to an area with a positive charge.

As the electrons zip along through the filament, they are constantly bumping into the atoms that make up the filament. The energy of each impact vibrates an atom — in other words, the current heats the atoms up. A thinner conductor heats up more easily than a thicker conductor because it is more resistant to the movement of electrons.

Electrons that are tightly bound inside the vibrating atoms can be temporarily boosted to a higher level of energy. When they come back down to their natural levels, extra energy is released in the form of photons. Infrared light is what is mostly produced by metal atoms, which is not visible to the human eye. However if the heat level gets high enough, (for a light bulb, 2200 degrees C/4000 degrees F) they will produce lots of visible light.

The filament in a light bulb is made of a long, incredibly thin length of tungsten metal. Tungsten is used in nearly all incandescent light bulbs because it is an ideal filament material. Most metals will actually melt before reaching such extreme temperatures — the vibration will break apart the rigid structural bonds between the atoms so that the material becomes a liquid. Light bulbs are manufactured with tungsten filaments because tungsten has an abnormally high melting temperature. But tungsten will catch on fire at such high temperatures, if the conditions are right. Combustion is caused by a reaction between two chemicals, which is set off when one of the chemicals has reached its ignition temperature. On Earth, combustion is usually a reaction between oxygen in the atmosphere and some heated material, but other combinations of chemicals will combust as well. The filament in a light bulb is housed in a sealed, oxygen-free chamber to prevent combustion. In the first light bulbs, all the air was sucked out of the bulb to create a near vacuum — an area with no matter in it. Since there wasn’t any gaseous matter present (or hardly any), the material could not combust.

The problem with this approach was the evaporation of the tungsten atoms. At such extreme temperatures, the occasional tungsten atom vibrates enough to detach from the atoms around it and flies into the air. In a vacuum bulb, free tungsten atoms shoot out in a straight line and collect on the inside of the glass. As more and more atoms evaporate, the filament starts to disintegrate, and the glass starts to get darker. This reduces the life of the bulb considerably.

In a modern light bulb, inert gases, typically argon, greatly reduce this loss of tungsten. When a tungsten atom evaporates, chances are it will collide with an argon atom and bounce right back toward the filament, where it will rejoin the solid structure. Since inert gases normally don’t react with other elements, there is no chance of the elements combining in a combustion reaction.

The modern incandescent light bulbs emit the majority of their energy as heat-carrying photons. Only around 10% of the light porduced by these bulbs in actually in the visible spectrum. This is quite a big waste of electricity. Sources of “cool light” like LEDs anf fluorescent lamps don’t waste a great deal of energy producing heat, the majority of what they emit is just visible light and this is the reason that they slowly phasing out the old reliable light bulb.

Tags: consumer electronics, Electrical appliances, electronics, gardening, home, home-and-garden, household, lamps, Light Bulbs, lighting, lights

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