Light Bulbs and Electrical Resistance

Incandescent light bulbs require electrical resistance.

Light bulbs depend on electricity; and although electrical current allows the bulbs to operate in several ways, the most important quality (at least for incandescent lights) is electrical resistance. Without resistance, these bulbs could not produce light at all; moreover, the type of resistance the bulb has controls the quality of the light itself.

Incandescents

Incandescent lights use a filament to produce light. An electrical current runs through this filament, creating a large amount of heat and, in the presence of enough energy, light. This filament is surrounded by the glass bulb, which protects it from outside air, which would quickly oxidize the filament and cause it to burn out.

Filaments

In modern incandescent bulbs, the most common filament material is tungsten. The filament must be a very strong metal that can resist great amounts of heat because the electrical resistance that builds up, as the bulb creates light, can reach thousands of degrees Celsius. As electricity passes through the filament, the metal resists the passage of the energy. Some energy is slowed, and escapes the metal as heat and light. The more durable the filament, the longer the bulb lasts.

Temperature

Temperature is an important indication of electrical resistance in an incandescent light bulb. The higher the temperature, the more current is flowing through the filament and the greater the wattage of the bulb. This makes the bulb brighter, but there is a drawback. Filaments have innate resistance and can only handle so much current. A higher temperature will wear out a filament must faster.

Efficiency

Electrical resistance is not the best way to create light. It takes a large amount of energy to heat a filament until it produces light, and most of the energy released is in the form of heat waves. Fluorescent bulbs, which use a gas instead of electrical resistance, are more efficient although their light has a cooler look.

Gases

While bulbs have electrical resistance according to their filaments, the gases that surround the bulb are also important. They keep the filament from degrading as quickly under intense current. Noble gases with inert properties, such as argon, are often used in incandescent bulbs to supplement the filament.

LEDs

LED, or light-emitting diode, lights are a special type of circuit. When activated, these circuits produce light instead of heat. They also use a form of resistance, but the materials and process are very different from those used in incandescent bulbs.

References

• Molecular Expressions: Resistance at the Molecular Level
• Don Klipstein's Web Site: The Great Internet Light Bulb Book, Part I