What Is Incandescent Light?

What Incandescent Light Bulbs Are and Why You Can't Find Them Anymore

light bulb
Jeff Kubina/Flickr/CC BY 2.0

An incandescent light bulb or light source is any device that uses electricity to heat a filament - or wire - until it is hot enough to glow white. If that was done in the open air, in the presence of oxygen, the metal filament would burn up before it got that hot.

Incandescent bulbs work because the heated filament is inside a glass shell or globe that is evacuated and either left as a vacuum or filled with an inert gas. The wire can’t burn in a vacuum and it can’t burn if the only gas inside the bulb is inert and won’t react with it.

Who invented the incandescent light bulb?

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 oxygenless enclosure, and had produced a bulb that would last for forty hours. The incandescent bulb has come a long way since then.

Why do incandescent light bulbs burn out?

What happens is that the wire filament slowly evaporates. In an ordinary incandescent bulb, those molecules are simply lost. They 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. Of course, this also means that the filament wire is shrinking as it loses molecules. At some point, it winds up so thin that it can’t carry the current anymore, and it overheats and breaks. That’s when we say that the light bulb “blew” and we replace it.

Why can’t I still buy them?

They’re inefficient. In order to extend the life of standard incandescent bulbs, manufacturers build them to become less hot than the optimum temperature for emitting clear, white light. As a result, incandescent bulbs emit a lot of the energy they use in the infrared portion of the spectrum. That does us no good for seeing, of course, and is pretty much a waste of energy – unless we actually want the heat they are throwing off.

Have they been banned?

In a word, no. Incandescent bulbs haven’t been banned. What has happened is that all light bulbs are now required to meet a minimum efficiency standard, which was adopted in the Energy Independence and Security Act of 2007. Most standard incandescent light bulbs can’t meet those standards, but one that did could still be manufactured and sold. Still, a number of incandescent light bulbs were exempted from the standards. Three-way bulbs, rough service bulbs, and appliance bulbs are examples.

In the meantime, the manufacturers have been working to produce alternative light bulbs that meet the standards, produce good, pleasant light, and don’t cost three fortunes. The replacements for a standard 60W bulb, which was one of the earliest types of bulb affected, have come a long way toward meeting those standards.