A hollow glass ball with an opening at one end sealed with metal, usually about 7 centimetres in diameter, containg a wire that produces light when electricity is run through it. Conventional lightbulbs are fairly inefficient and thus also produce a lot of heat.

The metal casing on the non-round end has a spiral groove designed to let the lightbulb lock in to place in a socket in a lamp or a ceiling or wall fixture. Thus, changing a lightbulb is referred to as screwing. This casing is metal to conduct electricity, and connects with two metal leads in the socket to complete a circuit, one touching the tip, one touching the side.

There are many different sizes, wattages, and varieties of lightbulbs. In general, the lower the wattage, the dimmer the light produced, however there are many low-energy fluorescent bulbs which, while expensive, are more efficient and produce a bright light at a great energy savings. Halogen bulbs, which require a special fixture and are tricky to replace, produce the brightest light and are long lasting.

Lightbulbs are a perennial favourite topic of insulting jokes, usually in the form of "How many (members of some group) does it take to change a lightbulb?", playing on the idea that changing a lightbulb is such a simple task that it would take great stupidity to foul up. See: Lightbulb jokes. In practice, changing a lightbulb isn't easy, damnit. Lightbulbs are usually too high to comfortably reach, are very hot to the touch if they've just just burned out, and you have to change them in the dark or holding a flashlight in your teeth (god help you if your flashlight burns out too), and even if you're in a well-lit room, you can't see the socket while you screw the lightbulb in. There's no easy way to test if the connection is completed other than by turning it on, which can leave you with a hot lightbulb in your hand suddenly when the connection closes, and finally, many lamp switches and wall switches leave it ambiguous as to whether they are in the on position or not in the absence of a functionning lightbulb. So what if it takes 17 of you, one to hold the bulb and 16 to turn the house! At least you have moral support! (grin)

Thomas Alva Edison is credited with the invention of the lightbulb.

In some suspiciously foreign countries, there is a sinister alternative to the wholesome Amurrican screw-in light bulb, known as the bayonet bulb.

No one knows whether this threat to our way of illumination arose out of innocent mechanical engineering efforts, a socialist conspiracy, or the anemic diet of said foreigners. I suspect it had to do with use in marine or otherwise damp environments, where corrosion would inevitably make screw-in bulbs difficult to remove from their sockets.

Whatever its origin and purpose, this perversion of incandescence takes the form of a lightbulb with no grooves on the metal base, but instead a pair of opposed prongs about 2 millimeters long, designed to fit into corresponding L-shaped slots in a similarly grooveless socket. To install, press the bulb into the spring-loaded socket and apply a quarter-turn of rotation. Then release pressure, allowing the prongs to seat themselves in the detents at the end of the slots that prevent unsavory counter-revolutionary forces from loosening the bulb.

Right-thinking citizens will naturally reject this effete and unnecessary attempt to insert the thin end of the Metric wedge into the great edifice of Imperial Measures.

Oceania has ALWAYS been at war with Eastasia.

A lightbulb, quite simply, is a small metal wire that is glowing from heat dissipation. Most common lightbulbs are made from the metal tungsten (W on the Periodic Table). Tungsten is used because it remains solid at very high temperatures. Most of the air is sucked out of the bulb, forming a semi-vacuum. If a vacuum isn't acheived, the tungsten would burn out immediately. When a light bulb "burns out", the filament slowly vaporizes; the black on the inside of a burned out lightbulb is really just resolidified metal vapor.

The actual process of creating light is very simple. Electricity flowing through the wire causes the tungsten to heat up and begin to glow (similar to molten steel glowing white hot). It heats up due to its resistance. When electricity passes through something, the substance it is passing through tries to hold on to the electrons. The electrons have to be forced through, and some of this force is absorbed by the metal and given off as heat. As the tungsten filament heats up, it gives off light.

The heat energy goes into electrons of the tungsten atoms. The energy pushes the electrons farther away from the nucleus of the atoms (they move up in energy level). As the electrons fall back to their original energy level, they give off photons which are really little bits of light.

Fluorescent lightbulbs work similarly. Electricity moves in pulses through a tube. The electricity hits the molecules inside the tube and their electrons are knocked away. As their electrons fall back, light is given off. In this case, the electrons are knocked off by electrictiy, not heat, and therefore, fluorescent lightbulbs can be cooler. Because they are cooler, nothing vaporizes, and the fluorescent lightbulb lasts longer.

Henry Woodward and Mathew Evans filed a patent in Canada for their light bulb invention on July 24, 1874. The patent predates Thomas Edison's U.S. patent by about five years.

Some have claimed that the Edison light bulb was more advanced than the Woodward and Evans bulb but the reverse is actually the case. Woodward and Evans's bulb was filled with nitrogen, a relatively inert gas which won't react with the carbon filament in the bulb. In contrast, Edison's design called for the bulb to contain a near perfect vacuum. Today, light bulbs of more than about 40 watts contain a mixture of gases which are selected because they are relatively inert (argon and nitrogen being the most common).

Thomas Edison later purchased an interest in the Woodward and Evans patent - a pretty strong indication that Edison felt that the Woodward and Evans light bulb patent was a threat.

It should be noted that Sir Humphry Davy, an English chemist, produced light using electrically heated strips of platinum in 1802. The problem was that the strips quickly burned out although the race was on and inventors around the world joined in. Later, in about 1860, Sir Joseph Wilson Swan, an English physicist, used carbon filaments in an evacuated glass bulb to produce light. Unfortunately, the filaments quickly burned out due to air in the bulb and the bulb wasn't particularily efficient. Swan did produce an apparently successful light in 1878 put didn't patent it in time.

There's another twist to the story - although Edison filed his patent application in 1879, the U.S. Patent Office ruled on October 8, 1883 that Edison's patent was invalid on the basis of prior art by William Sawyer and Albon Man.

Ok. So Edison's patent was invalid. Right? Well, as it turns out, not quite . . . on October 6, 1889 a court ruled that one of Edison's claims relating to the use of "a filament of carbon of high resistance" was valid.

But we're still not done . . . in 1979, Robert Conot published a book called A Streak of Luck. In the book, Conot reveals that Edison and his attorneys withheld evidence. Specifically, they removed the October 7-12, 1879 part of a notebook before providing the rest of the notebook to the court. The missing pages showed that Edison really was just expanding on prior art by Sawyer and/or Swan!

The bottom line is that although one can debate who did invent the light bulb, there seems to be little doubt that Edison didn't!

Edison can be given credit for commercializing the light bulb.


  • a photocopy of the Woodward and Evans patent (obtained from CIPO - Canadian Intellectual Property Office (i.e. the Canadian Patent Office))
  • a photocopy of an undated article from EUREKA! magazine (reprinted from the Toronto Star)
  • a biography of Sir Joseph Swan at http://www.acmi.net.au/AIC/SWAN_BIO.html (last accessed 2002/09/27)
  • a fairly detailed discussion of Edison's light bulb and patent saga located at http://www.willitsell.com/edisnmth.htm (last accessed 2002/09/27)

Similar to the notion of referring to an adhesive medical strip as a Band-Aid or facial tissue as Kleenex, when most people say "light bulb", they actually mean lamp. It is a matter of the correct technical term not being used in the common parlance. Likewise, when most people say "lamp", what they actually mean is light fixture or instrument. Most electrical engineers will tell a layman that the bulb is only the translucent casing (usually some form of glass) which holds in the gases used in the incandescent or fluorescent process.

As the joke goes...

Layman: How many electricians does it take to screw in a light bulb?
Electrician: It's called a lamp!

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