What Is an Incandescent Light Bulb?

Light Bulb On Wooden Table
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The light bulb design popularized by Thomas Edison in the late 1800s, and used widely with only slight modifications ever since, is known as an incandescent light bulb (or more accurately an incandescent lamp). It has only been since the 1990s that other lightbulb styles, such as CFL (compact fluorescent lamp) and LED (light-emitting diode) designs have begun to erode the popularity of incandescents for residential use.

Popular though they have been, incandescent light bulbs are very inefficient in their use of electricity, and they are gradually being phased out for environmental reasons. Recognizing that poor energy efficiency translates into greater greenhouse gas emissions, virtually all forward-thinking nations have initiated bans or gradual phase-outs of inefficient light bulbs, such as the incandescent design.

What Is an Incandescent Light Bulb?

An incandescent light bulb is a glass and metal device that produces light when a thin wire filament glows with illumination as it is heated by an electrical current passing through it. "Incandescent" essentially means "light produced by heat radiation."

Parts of an Incandescent Light Bulb

The standard incandescent light bulb is a fairly simple device. A threaded metal base (known as an Edison base) is linked to a fine tungsten metal filament that is coiled within a glass bulb mounted to the metal base with sealed joints. Historically, the glass bulb containing the filament was evacuated to create a partial vacuum devoid of air, but most modern bulbs above 25 watts are now filled with an inert gas (usually argon) with a small amount of nitrogen. Without air and oxygen inside the bulb, the filament is more resistant to being consumed and burning out.

When the bulb is screwed into the socket of a light fixture or lamp, turning on the fixture causes circuit electrical current to flow through the outer shell of the bulb base, into the airless bulb and through the thin wire filament, then out of the bulb through a contact point in the center of the bulb's base. The electrical current passing through the thin wire creates a high resistance that causes the bulb's filament to heat up and glow with light.

There are several variations in this design. Many bulbs now have silica powder coating the inside of the glass, diffusing the light into a "soft white" glow. Varying the composition of the filament and the type of inert gas filling the bulb can create different levels of brightness and light color. A halogen bulb, for example, is an incandescent variation that uses halogen gas inside the bulb to create a much longer-lived bulb.

When a light bulb burns out, it is the end result of the wire filament slowly evaporating. In an ordinary incandescent bulb, those molecules evaporating off the filament wind up deposited on the inside of the glass shell, which is why an older incandescent bulb will look yellower and dimmer than an otherwise identical new one. This also means that the filament wire is shrinking as it loses molecules. At some point, it becomes so thin that it can’t carry the current anymore, at which point it overheats and breaks—"blowing out."

History Lesson

It was two earlier inventors, Henry Woodward, and Matthew Evans, who invented the incandescent light bulb, whose patent was purchased by Thomas Edison. By 1879, Edison had switched to a carbon filament and the oxygen-less enclosure, and had produced a bulb that lasted initially for over fourteen hours. The incandescent bulb has come a long way since then, with bulbs now filled with inert gas and using filaments made from tungsten metal. Modern incandescent bulbs can provide 1,000 hours or more of service.

Drawbacks of Incandescent Light Bulbs

While this light bulb design has been improved over the decades, the incandescent design remains a relatively inefficient way to produce light. Standard incandescent bulbs convert no more than 10 percent of their consumed energy as visible light, making them relatively expensive to use in terms of energy cost. Other drawbacks include:

  • Short life: A typical incandescent light bulb will provide about 750 to 2,000 hours of service. By comparison, a screw-in compact fluorescent bulb will provide 8,000 to 10,000 hours of life, and an LED bulb might last 40,000 to 50,000 hours.
  • Heat: At least 90 percent of the bulb's energy consumption is dissipated as heat. This can damage light fixtures and wiring, and even pose a fire hazard. These bulbs are very wasteful of energy and hence expensive to operate when compared to other alternatives.
  • Highly fragile: Incandescent bulbs use very thin glass shells and can crack or shatter at the smallest provocation. LED and fluorescent bulbs are considerably sturdier.

The drawbacks of this bulb design—especially the high energy consumption— have led to efforts to discourage the use of incandescent bulbs by establishing higher minimum standards for energy efficiency. European Union nations, along with Russia, Canada, and Mexico are among those that are gradually phasing out most standard incandescent light bulbs.

In the U.S., the effort to reduce and eliminate the sale of inefficient incandescent bulbs has been a hotly debated issue, producing policies that change frequently as political winds shift. Under current leadership, though, energy-efficiency standards will lead to the end of most incandescent lightbulb sales by the end of 2023.

It's important to note that it is not the bulbs themselves that are being banned. Instead, the U.S. is now setting higher minimum efficiency standards, based on the Energy Independence and Security Act of 2007. Most standard incandescent light bulbs can’t meet those standards, but the ones that do will continue to be manufactured and sold. And some incandescent light bulbs are exempted from the standards—three-way bulbs, chandelier bulbs, and appliance bulbs are examples.

Benefits of Incandescent Light Bulbs

Considering how wasteful these bulbs are in terms of energy consumption, there are only a few meaningful benefits to consider:

  • Natural-colored light: Incandescent light bulbs produce light that is very close to the color of natural sunlight. This advantage is no longer as important, though, as LED bulbs have now been improved to produce a similarly pleasing color. In professional photography, there is sometimes an aesthetic advantage to lighting with incandescent lamps.
  • Heat-producing: In situations where heat is actually desired (bathroom heat lamps, food-warming lamps, etc.) incandescent bulbs can be a safe way to produce heat.
  • Can be dimmed easily: Incandescent bulbs can work with old-style dimmer switches to vary the light output. But this advantage has also been largely eliminated by newer designs in CLF and LED technology, which now allow those bulbs to be controlled by dimmer switches, too.
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  1. Understanding a Lightbulb's Lifespan. Greencents.