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12 janvier 2011 3 12 /01 /janvier /2011 05:02

The incandescent light bulb, incandescent lamp or incandescent light globe makes light by heating a metal filament wire to a high temperature until itglows. The hot filament is protected from air by a glass bulb that is filled with inert gas or evacuated  (Dell XPS M1210 Batteryhttp://www.hdd-shop.co.uk .

In a halogen lamp, a chemical process that returns metal to the filament prevents its evaporation. The light bulb is supplied with electrical current by feed-through terminals or wires embedded in the glass. Most lamps are used in a socket  (Dell Studio XPS 1340 Battery)    .

Incandescent bulbs are produced in a wide range of sizes, light output, and voltage ratings, from 1.5 volts to about 300 volts. They require no external regulating equipment and have a low manufacturing cost and work equally well on either alternating current or direct current  (Dell Studio XPS 1640 Battery)      .

As a result, the incandescent lamp is widely used in household and commercial lighting, for portable lighting such as table lamps, car headlamps, and flashlights, and for decorative and advertising lighting  (Dell Studio XPS 1640 Battery)   .

Some applications of the incandescent bulb use the heat generated by the filament, such as incubators, brooding boxes for poultry, heat lights for reptiletanks, infrared heating for industrial heating and drying processes, and the Easy-Bake Oven toy  (Dell Vostro 1710 Battery)     .

In cold weather, the heat produced by incandescent lamps contributes to building heating, but in hot climates lamp losses increase the energy used by air conditioning systems     .

Incandescent light bulbs are gradually being replaced in many applications by other types of electric lights  (Dell KM958 battery) ,

such as fluorescent lamps, compact fluorescent lamps, cold cathode fluorescent lamps (CCFL), high-intensity discharge lamps, and light-emitting diodes (LEDs). These newer technologies improve the ratio of visible light to heat generation. Some jurisdictions, such as the European Union     (Sony VGP-BPS13 battery)      ,

are in the process of phasing out the use of incandescent light bulbs in favor of more energy-efficient lighting. In the United States, federal law has scheduled incandescent light bulbs to be phased out by 2014, to be replaced with more energy-efficient light bulbs.In Brazil, they have already been phased out  (Sony VGP-BPS13/B battery)     .

History of the light bulb

In addressing the question of who invented the incandescent lamp, historians Robert Friedel and Paul Israel list 22 inventors of incandescent lamps prior to Joseph Wilson Swanand Thomas Edison   (Sony VGP-BPS13/S battery)     .

They conclude that Edison's version was able to outstrip the others because of a combination of three factors: an effective incandescent material, a highervacuum than others were able to achieve (by use of the Sprengel pump) and a high resistance that made power distribution from a centralized source economically viable   (Sony VGP-BPS13A/B battery)    .

Another historian, Thomas Hughes, has attributed Edison's success to the fact that he invented an entire, integrated system of electric lighting.

The lamp was a small component in his system of electric lighting    (Sony VGP-BPS13B/B battery)     ,

and no more critical to its effective functioning than the Edison Jumbo generator, the Edison main and feeder, and the parallel-distribution system. Other inventors with generators and incandescent lamps, and with comparable ingenuity and excellence, have long been forgotten because their creators did not preside over their introduction in a system of lighting  (Sony VGP-BPL9 battery) .

Historian Thomas P. Hughes

Early pre-commercial research

In 1802, Humphry Davy had what was then the most powerful electrical battery in the world at the Royal Institution of Great Britain  (Sony VGP-BPS13B/B battery)      .

In that year, he created the first incandescent light by passing the current through a thin strip ofplatinum, chosen because the metal had an extremely high melting point. It was not bright enough nor did it last long enough to be practical, but it was the precedent behind the efforts of scores of experimenters over the next 75 years        Sony VGP-BPL15 battery .

In 1809, Davy also created the first arc lamp with two carbon charcoal rods connected to a 2000-cell battery; it was demonstrated to the Royal Institution in 1810.

Over the first three-quarters of the 19th century many experimenters worked with various combinations of platinum or iridium wires, carbon rods, and evacuated or semi-evacuated enclosures  Dell Inspiron E1505 battery .

Many of these devices were demonstrated and some were patented.

In 1835, James Bowman Lindsay demonstrated a constant electric light at a public meeting in Dundee, Scotland. He stated that he could "read a book at a distance of one and a half feet"  Dell Latitude E6400 battery .

However, having perfected the device to his own satisfaction, he turned to the problem of wireless telegraphy and did not develop the electric light any further. His claims are not well documented, although he is credited in Challoner etal. with being the inventor of the "Incandescent Light Bulb"  HP Pavilion dv6000 Battery .

In 1840, British scientist Warren de la Rue enclosed a coiled platinum filament in a vacuum tube and passed anelectric current through it. The design was based on the concept that the high melting point of platinum would allow it to operate at high temperatures and that the evacuated chamber would contain fewer gas molecules to react with the platinum SONY VAIO VGN-FZ Battery ,

improving its longevity. Although an efficient design, the cost of the platinum made it impractical for commercial use.

In 1841, Frederick de Moleyns of England was granted the first patent for an incandescent lamp, with a design using platinum wires contained within a vacuum bulb      SONY VAIO VGN-FZ18 Battery .

In 1845, American John W. Starr  acquired a patent for his incandescent light bulb involving the use of carbon filaments. He died shortly after obtaining the patent, and his invention was never produced commercially. Little else is known about him  SONY VAIO VGN-FZ180E Battery .

In 1851, Jean Eugène Robert-Houdin publicly demonstrated incandescent light bulbs on his estate in Blois, France. His light bulbs are on permanent display in the museum of the Château de Blois.

In 1872 Russian A. N. Lodygin invented an incandescent light bulb and obtained a Russian privilege  SONY VAIO VGN-FZ220E Battery .

In 1874 he obtained an American patent for his invention. Later he applied and obtained patents for incandescent lamps havingmolybdenum and tungsten filaments, which were then demonstrated at the Exposition Universelle of 1900 inParis  SONY VAIO VGN-FZ340E Battery .

In a suit filed by rivals seeking to get around Edison's lightbulb patent, German-American inventor Heinrich Göbelclaimed he developed the first light bulb in 1854: a carbonized bamboo filament, in a vacuum bottle to prevent oxidation, and that in the following five years he developed what many call the first practical light bulb   SONY VAIO VGN-FZ430E Battery .

Despite a successful recreation of his lamp in 1882, Lewis Latimer demonstrated that the bulbs which Göbel had purportedly built in the 1850s, had actually been built much later, and found the glassblower who had constructed the fraudulent exhibits. In a patent interference suit in 1893, the judge ruled Göbel's claim "extremely improbable"    SONY VAIO VGN-FZ460E Battery .

In North America, parallel developments were taking place. On July 24, 1874 a Canadian patent was filed by aToronto medical electrician named Henry Woodward and a colleague Mathew Evans. They built their lamps with different sizes and shapes of carbon rods held between electrodes in glass cylinders filled with nitrogen     SONY VAIO VGN-FZ480E Battery .

Woodward and Evans attempted to commercialize their lamp, but were unsuccessful. They ended up selling their patent (U.S. Patent 0,181,613) to Thomas Edison in 1879.


Carbon filament lamp (E27 socket, 220volts, approx. 30 watts, left side: running with 100 volts)  SONY VAIO VGN-FZ4000 Battery .

Joseph Wilson Swan (1828–1914) was a British physicist and chemist. In 1850, he began working with carbonized paper filaments in an evacuated glass bulb. By 1860 he was able to demonstrate a working device but the lack of a good vacuum and an adequate supply of electricity resulted in a short lifetime for the bulb and an inefficient source of light  SONY VAIO VGN-FZ31E Battery .

By the mid-1870s better pumps became available, and Swan returned to his experiments.

With the help of Charles Stearn, an expert on vacuum pumps, in 1878 Swan developed a method of processing that avoided the early bulb blackening. This received a British Patent No 8 in 1880       SONY VAIO VGN-FZ31B Battery .

On 18 December 1878 a lamp using a slender carbon rod was shown at a meeting of the Newcastle Chemical Society, and Swan gave a working demonstration at their meeting on 17 January 1879. It was also shown to 700 who attended a meeting of the Literary and Philosophical Society of Newcastle on 3 February 1879      SONY VAIO VGN-FZ31J Battery .

These lamps used a carbon rod from an arc lamp rather than a slender filament. Thus they had low resistance and required very large conductors to supply the necessary current, so they were not commercially practical, although they did furnish a demonstration of the possibilities of incandescent lighting with relatively high vacuum, a carbon conductor, and platinum lead-in wires  SONY VAIO VGN-FZ31M Battery .

Besides requiring too much current for a central station electric system to be practical, they had a very short lifetime. Swan turned his attention to producing a better carbon filament and the means of attaching its ends. He devised a method of treating cotton to produce 'parchmentised thread' and obtained British Patent 4933 in 1880  SONY VAIO VGN-FZ31Z Battery .

From this year he began installing light bulbs in homes and landmarks in England. His house was the first in the world to be lit by a lightbulb and so the first house in the world to be lit by Hydro Electric power. In the early 1880s he had started his company  SONY VAIO VGN-FZ38M Battery .

In 1881, the Savoy Theatre in the City of Westminister, London was lit by Swan incandescent lightbulbs, which was the first theatre, and the first public building in the world, to be lit entirely by electricity.

Thomas Edison began serious research into developing a practical incandescent lamp in 1878  SONY VGP-BPS8 Battery .

Edison filed his first patent application for "Improvement In Electric Lights" on October 14, 1878 (U.S. Patent 0,214,636). After many experiments with platinum and other metal filaments, Edison returned to a carbon filament. The first successful test was on October 22, 1879, and lasted 13.5 hours  SONY VGP-BPS13 Battery .

Edison continued to improve this design and by November 4, 1879, filed for a U.S. patent for an electric lamp using "a carbon filament or strip coiled and connected ... to platina contact wires."  Although the patent described several ways of creating the carbon filament including using "cotton and linen thread  SONY VGP-BPS13/S Battery ,

wood splints, papers coiled in various ways,"it was not until several months after the patent was granted that Edison and his team discovered that a carbonized bamboo filament could last over 1200 hours.

Hiram S. Maxim started a lightbulb company in 1878 to exploit his patents and those of William Sawyer  SONY VGP-BPS13A/B Battery .

His United States Electric Lighting Company was the second company, after Edison, to sell practical incandescent electric lamps. They made their first commercial installation of incandescent lamps at the Mercantile Safe Deposit Company in New York City in the fall of 1880, about six months after the Edison incandescent lamps had been installed on the steamer Columbia  SONY VGP-BPS13B/B Battery .

In October 1880, Maxim patented a method of coating carbon filaments with hydrocarbons to extend their life.Lewis Latimer, his employee at the time, developed an improved method of heat-treating them which reduced breakage and allowed them to be molded into novel shapes, such as the characteristic "M" shape of Maxim filaments    SONY VGP-BPS13A/S Battery .

On January 17, 1882, Latimer received a patent for the "Process of Manufacturing Carbons," an improved method for the production of light bulb filaments which was purchased by the United States Electric Light Company. Latimer patented other improvements such as a better way of attaching filaments to their wire supports   SONY VGP-BPS13AS Battery .

In Britain, the Edison and Swan companies merged into the Edison and Swan United Electric Company (later known as Ediswan, which was ultimately incorporated into Thorn Lighting Ltd). Edison was initially against this combination, but after Swan sued him and won, Edison was eventually forced to cooperate, and the merger was made  Dell Inspiron 1320n Battery .

Eventually, Edison acquired all of Swan's interest in the company. Swan sold his United States patent rights to the Brush Electric Company in June 1882.

In 1882, the first recorded set of miniature incandescent lamps for lighting a Christmas tree was installed   Dell Inspiron 1464 Battery.

These did not become common in homes for many years.

The United States Patent Office gave a ruling October 8, 1883, that Edison's patents were based on the prior art of William Sawyer and were invalid. Litigation continued for a number of years     Dell Inspiron 1564 Battery .

Eventually on October 6, 1889, a judge ruled that Edison's electric light improvement claim for "a filament of carbon of high resistance" was valid      Dell Inspiron 1764 Battery .

In the 1890s, the Austrian inventor Carl Auer von Welsbach worked on metal-filament mantles, first with platinum wire, and then osmium, and produced an operating version in 1898. In 1898 he patented the osmium lamp and started marketing it in 1902, the first commercial metal filament incandescent lamp    Dell Studio 1450 Battery .

In 1897, German physicist and chemist Walther Nernst developed the Nernst lamp, a form of incandescent lamp that used a ceramic globar and did not require enclosure in a vacuum or inert gas. Twice as efficient as carbon filament lamps, Nernst lamps were briefly popular until overtaken by lamps using metal filaments    Dell Studio 1457 Battery .

In 1903, Willis Whitnew invented a metal-coated carbon filament that would not blacken the inside of a light bulb.

On December 13, 1904, Hungarian Sándor Just and Croatian Franjo Hanaman were granted a Hungarian patent (No. 34541) for a tungsten filament lamp, which lasted longer and gave a brighter light than the carbon filament  Dell Latitude D610 Battery .

Tungsten filament lamps were first marketed by the Hungarian company Tungsram in 1905, so this type is often called Tungsram-bulbs in many European countries       Toshiba NB100 Battery .

In 1906, the General Electric Company patented a method of making filaments from sintered tungsten and in 1911 used ductile tungsten wire for incandescent light bulbs. The tungsten filament outlasted all other types       Toshiba Satellite M65 battery .

In 1913 Irving Langmuir found that filling a lamp with inert gas instead of a vacuum resulted in twice the luminous efficacy and reduction of bulb blackening. In 1924, Marvin Pipkin, an American chemist, patented a process for frosting the inside of lamp bulbs without weakening them, and in 1947 he patented a process for coating the inside of lamps with silica  Toshiba Satellite M60 battery .

In 1930, Hungarian Imre Bródy filled lamps with krypton gas in lieu of argon. He used krypton and/or xenon filling of bulbs. Since the new gas was expensive, he developed a process with his colleagues to obtain krypton from air. Production of krypton filled lamps based on his invention started at Ajka in 1937, in a factory co-designed by Polányi and Hungarian-born physicist Egon Orowan  Dell Latitude D830 Battery .

By 1964, improvements in efficiency and production of incandescent lamps had reduced the cost of providing a given quantity of light by a factor of thirty, compared with the cost at introduction of Edison's lighting system

Consumption of incandescent light bulbs grew rapidly in the United States  Dell Latitude D620 Battery .

In 1885 an estimated 300,000 general lighting service lamps were sold, all with carbon filaments. When tungsten filament were introduced, there were about 50 million lamp sockets in the United States. In 1914 88.5 million lamps were used, (only 15% with carbon filaments), and by 1945 annual sales of lamps were 795 million (more than 5 lamps per person per year)  Dell Inspiron Mini 10 Battery .


Main article: Phoebus cartel

Between 1924 and 1939 the international market for incandescent light bulbs was controlled by the Phoebus cartel, which dictated wholesale prices and whose members controlled most of the world market for lamps  Sony VGN-FW11S Battery .

Efficiency comparisons

Approximately 90% of the power consumed by an incandescent light bulb is emitted as heat, rather than as visible light.

The effectiveness of an electric lighting source is determined by two factors, the relative visibility of electromagnetic radiation, and the rate at which the source converts electric power into electromagnetic radiation     Sony VGN-FW11M Battery .

Luminous efficacy of a light source is a ratio of the visible light energy emitted (the luminous flux) to the total power input to the lamp. Visible light is measured inlumens, a unit which is defined in part by the differing sensitivity of the human eye to different wavelengths of light     Sony VGN-FW139E/H battery .

Not all wavelengths of visible electromagnetic energy are equally effective at stimulating the human eye; the luminous efficacy of radiant energy is a measure of how well the distribution of energy matches the perception of the eye. The maximum efficacy possible is 683 lm/W for monochromatic green light at 555 nanometres wavelength, the peak sensitivity of the human eye  Dell Latitude E5400 Battery .

For white light, the maximum luminous efficacy is around 240 lumens per watt, but the exact value is not unique because the human eye can perceive many different mixtures of visible light as "white"      Dell Latitude E4200 Battery .

The chart below lists values of overall luminous efficacy and efficiency for several types of general service, 120 volt, 1000-hour lifespan incandescent bulb, and several idealized light sources. A similar chart in the article on luminous efficacy compares a broader array of light sources to one another       Dell Inspiron 300M Battery .

Unfortunately, the spectrum emitted by a blackbody radiator does not match the sensitivity characteristics of the human eye. Tungsten filaments radiate mostly infrared radiation at temperatures where they remain solid (below 3683 kelvins / 3410°C / 6,170°F)     Dell Vostro A840 Battery .

Donald L. Klipstein explains it this way: "An ideal thermal radiator produces visible light most efficiently at temperatures around 6300 °C (6600 K or 11,500 °F). Even at this high temperature, a lot of the radiation is either infrared or ultraviolet, and the theoretical luminous efficiency is 95 lumens per watt      Dell Studio 1737 battery .

" No known material can be used as a filament at this ideal temperature, which is hotter than the sun's surface. An upper limit for incandescent lamp luminous efficacy is around 52 lumens per watt, the theoretical value emitted by tungsten at its melting point Dell Inspiron E1505 battery .

For a given quantity of light, an incandescent light bulb produces more heat (and consumes more power) than a fluorescent lamp. Incandescent lamps' heat output increases load on air conditioning in the summer, but the heat from lighting can contribute to building heating in cold weather      Dell RM791 battery .

High-quality halogen incandescent lamps have higher efficacy, which will allow a 60 W bulb to provide nearly as much light as a non-halogen 100 W. Also, a lower-wattage halogen lamp can be designed to produce the same amount of light as a 60 W non-halogen lamp, but with much longer life      Dell XPS M1530 battery .

Many light sources, such as the fluorescent lamp, high-intensity discharge lamps and LED lamps offer higher efficiency, and some have been designed to be retrofitted in existing fixtures. These devices produce light by luminescence, instead of heating a filament to incandescence     Dell XPS M2010 battery .

These mechanisms produce discrete spectral lines and so don't have the broad "tail" of wasted invisible infrared emissions produced by incandescent emitters. By careful selection of which electron energy level transitions are used, the spectrum emitted can be tuned to either mimic the appearance of incandescent sources or else produce different color temperatures of white for visible light  Acer Aspire One battery .

Cost of lighting

The initial cost of an incandescent bulb is small compared to the cost of the energy it uses over its lifetime. A comparison of incandescent lamp operating cost with other light sources must consider the luminous efficacy produced by each lamp  Toshiba Satellite P10 Battery .

The comparison must include illumination requirements, capital cost of the lamp, labor cost to replace lamps, various depreciation factors for light output as the lamp ages, effect of lamp operation on heating and air conditioning systems, and energy consumption as well    SONY VGN-FZ210CE Battery .

Measures to ban its use

Due to the higher energy usage of incandescent light bulbs in comparison to more energy efficient alternatives, such as compact fluorescent lamps and LED lamps, many governments have introduced measures to ban their use, by setting minimum efficacy standards higher than can be achieved by general service lamps     Dell Precision M70 Battery .

However, there has been much resistance to these policies owing to the low cost of incandescent bulbs, the instant availability of light, and possible ill health effects including the problems of mercury contamination with CFLs. Varying and unpredictable quality of current CFLs and LED lamps adds to the resistance      Toshiba Satellite L305 Battery .

Efforts to improve efficiency

Due to the measures noted above, there have been recent efforts to improve the efficiency of incandescents. In 2007 the consumer lighting division of General Electric announced a "high efficiency incandescent" (HEI) lamp project  Toshiba Satellite T4900 Battery ,

which they claimed would ultimately be as much as four times more efficient than current incandescents, although their initial production goal was to be approximately two times more efficient.The HEI program was quietly terminated in 2008 due to slow progress  Toshiba PA3399U-2BRS battery .

U.S. Department of Energy research at Sandia National Laboratories initially indicated the potential for dramatically improved efficiency from a photonic lattice filament. However, later work indicated that initially promising results were in error Toshiba Satellite A200 Battery .

Prompted by U.S. legislation mandating increased bulb efficiency by 2012, new "hybrid" incandescent bulbs have been introduced by Philips. The "Halogena Energy Saver" incandescent is 30 percent more efficient than traditional designs, using a special chamber to reflect formerly wasted heat back to the filament to provide additional lighting power  Toshiba Satellite 1200 Battery .


Incandescent light bulbs consist of a glass enclosure (the envelope, or bulb) with a filament of tungsten wire inside the bulb, through which an electric current is passed     Toshiba Satellite M300 Battery .

Contact wires and a base with two (or more) conductors provide electrical connections to the filament. Incandescent light bulbs usually contain a stem or glass mount anchored to the bulb's base which allows the electrical contacts to run through the envelope without gas/air leaks      Sony Vaio PCG-5G2L Battery .

Small wires embedded in the stem in turn support the filament and/or its lead wires. The bulb is filled with an inert gas such as argon to reduceevaporation and prevent oxidation of the filament      Sony Vaio PCG-5G3L Battery .

An electric current heats the filament to typically 2000 K to 3300 K (about 3100–5400°F), well below tungsten's melting point of 3695 K (6192°F). Filament temperatures depend on the filament type, shape, size, and amount of current drawn. The heated filament emits light that approximates a continuous spectrum       Sony Vaio PCG-5J1L Battery .

The useful part of the emitted energy is visible light, but most energy is given off asheat in the near-infrared wavelengths.

Three-way light bulbs have two filaments and three conducting contacts in their bases. The filaments share a common ground, and can be lit separately or together       Sony Vaio PCG-5K2L Battery .

Common wattages include 30–70–100, 50–100–150, and 100–200–300, with the first two numbers referring to the individual filaments, and the third giving the combined wattage        Sony Vaio PCG-5J2L Battery .

While most light bulbs have clear or frosted glass, other kinds are also produced, including the various colors used for Christmas tree lights and other decorative lighting. Neodymium-containing glass is sometimes used to provide a more natural-appearing light   Sony Vaio PCG-5K1L Battery .

Many arrangements of electrical contacts are used. Large lamps may have a screw base (one or more contacts at the tip, one at the shell) or a bayonet base (one or more contacts on the base, shell used as a contact or used only as a mechanical support). Some tubular lamps have an electrical contact at either end       Sony Vaio PCG-5L1L Battery .

Miniature lamps may have a wedge base and wire contacts, and some automotive and special purpose lamps have screw terminals for connection to wires. Contacts in the lamp socket allow the electric current to pass through the base to the filament. Power ratings for incandescent light bulbs range from about 0.1 watt to about 10,000 watts     Sony Vaio PCG-6S2L Battery .

The glass bulb of a general service lamp can reach temperatures between 200 and 260 degrees Celsius (400 to 550 degrees Fahrenheit). Lamps intended for high power operation or used for heating purposes will have envelopes made of hard glass or fused quartz     Sony Vaio PCG-6S3L Battery .


Early lamps were laboriously hand-assembled; however, after automatic machinery was developed cost of lamps fell.

In manufacturing the glass bulb, a type of "ribbon machine" is used     Sony Vaio PCG-6V1L Battery .

A continuous ribbon of glass is passed along a conveyor belt, heated in a furnace, and then blown by precisely aligned air nozzles through holes in the conveyor belt into molds. Thus the glass bulbs are created. After the bulbs are blown, and cooled, they are cut off of the ribbon machine      Sony Vaio PCG-6W1L Battery .

A typical machine of this sort produces 50,000 bulbs per hour.


The first successful light bulb filaments were made of carbon (from carbonized paper or bamboo). Early carbon filaments had a negative temperature coefficient of resistance -- as they got hotter, their electrical resistance decreased     Sony Vaio PCG-6W2L Battery .

This made the lamp sensitive to fluctuations in the power supply, since a small increase of voltage would cause the filament to heat up, reducing its resistance and causing it to draw even more power and heat even further. In the "flashing" process, carbon filaments were heated by current passing through them, while in an evacuated vessel containing hydrocarbon (gasoline) vapor Sony Vaio PCG-6W3L Battery .

The carbon deposited by this treatment improved the uniformity and strength of filaments, and their efficiency. A metallized or graphitized filament was first heated in a high-temperature oven before flashing and lamp assembly; this transformed the carbon into graphite  Sony Vaio PCG-7111L Battery ,

which further strengthened and smoothed the filament, and as a byproduct had the advantage of changing the lamp to a positive temperature coefficient like a metallic conductor. This helped stabilize power consumption, temperature and light output against minor variations in supply voltage     Sony Vaio PCG-7112L Battery .

In 1902 the Siemens company developed a tantalum lamp filament. These lamps were more efficient than even graphitized carbon filaments and could operate at higher temperatures. Since the metal had a lower resistivity than carbon, the tantalum lamp filament was quite long and required multiple internal supports   Sony Vaio PCG-7113L Battery .

The metal filament had the property of gradually shortening in use; the filaments were installed with large loops which tightened in use. This made lamps in use for several hundred hours quite fragile.Metal filaments had the property of breaking and re-welding, though this would usually decrease resistance and shorten the life of the filament     Sony Vaio PCG-7133L Battery .

General Electric bought the rights to use tantalum filaments and produced them in the United States until 1913.

From 1898 to around 1905 osmium was also used as a lamp filament in Europe, but the metal was so expensive that used broken lamps could be returned for part credit    Sony Vaio PCG-7Z2L Battery .

It could not be made for 110 V or 220 V so several lamps were wired in series for use on standard voltage circuits.

In 1906 the tungsten filament was introduced, which is still used. Tungsten metal was initially not available in a form that allowed it to be drawn into fine wires    Sony Vaio PCG-8Y1L Battery .

Filaments made from sintered tungsten powder were quite fragile. By 1910, a process was developed by William D. Coolidge at General Electric for production of a ductile form of tungsten. The process required pressing chemically produced tungsten powder into bars, then several steps of sintering, swaging, and then wire drawing     Sony Vaio PCG-8Y2L Battery .

It was found that very pure tungsten formed filaments that sagged in use, and that a very small "doping" treatment with potassium, silicon, and aluminum oxides at the level of a few hundred parts per million greatly improved the life and durability of the tungsten filaments       Sony Vaio PCG-8Z1L Battery .

To improve the efficiency of the lamp, the filament usually consists of coils of coiled fine wire, also known as a 'coiled coil.' For a 60-watt 120-volt lamp, the uncoiled length of the tungsten filament is usually 22.8 inches or 580 mm,and the filament diameter is 0.0018 inches (0.045 mm)      Sony Vaio PCG-8Z2L Battery .

The advantage of the coiled coil is that evaporation of the tungsten filament is at the rate of a tungsten cylinder having a diameter equal to that of the coiled coil. The coiled-coil filament evaporates more slowly than a straight filament of the same surface area and light-emitting power       Sony VAIO PCG-5G2L Battery .

If the filament is then run hotter to bring back evaporation to the same rate, the resulting filament is a more efficient light source.

There are several different shapes of filament used in lamps, with differing characteristics. Manufacturers designate the types with codes such as C-6, CC-6, C-2V, CC-2V, C-8, CC-88, C-2F, CC-2F, C-Bar, C-Bar-6, C-8I, C-2R, CC-2R, and Axial  Sony VAIO PCG-5G3L Battery .

Electrical filaments are also used in hot cathodes of fluorescent lamps and vacuum tubes as a source of electrons or in vacuum tubes to heat an electron-emitting electrode.

Reducing filament evaporation

One of the problems of the standard electric light bulb is evaporation of the filament      Sony VAIO PCG-5J1L Battery .

Small variations in resistivity along the filament cause "hot spots" to form at points of higher resistivity; a variation of diameter of only 1% will cause a 25% reduction in service life. The hot spots evaporate faster than the rest of the filament, increasing resistance at that point—a positive feedback which ends in the familiar tiny gap in an otherwise healthy-looking filament Sony VAIO PCG-5K2L Battery .

Irving Langmuir found that an inert gas, instead of vacuum, would retard evaporation. General service incandescent light bulbs over about 25 watts in rating are now filled with a mixture of mostly argon and some nitrogen, or sometimeskrypton. Xenon gas, much more expensive, is used occasionally in small bulbs, such as those for flashlights    Sony VAIO PCG-5J2L Battery .

Since a filament breaking in a gas-filled bulb can form an electric arc which may spread between the terminals and draw very heavy current, intentionally thin lead-in wires or more elaborate protection devices are therefore often used as fuses built into the light bulb. More nitrogen is used in higher-voltage lamps to reduce the possibility of arcing       Sony VAIO PCG-5K1L Battery .

During ordinary operation, the tungsten of the filament evaporates; hotter, more-efficient filaments evaporate faster. Because of this, the lifetime of a filament lamp is a trade-off between efficiency and longevity. The trade-off is typically set to provide a lifetime of several hundred to 2,000 hours for lamps used for general illumination    Sony VAIO PCG-5L1L Battery .

Theatrical, photographic, and projection lamps may have a useful life of only a few hours, trading life expectancy for high output in a compact form. Long-life general service lamps have lower efficiency but are used where the cost of changing the lamp is high compared to the value of energy used  Sony VAIO PCG-6S2L Battery .

Filament notching describes another phenomenon that limits the life of lamps. Lamps operated on direct current develop random stair-step irregularities on the filament surface, reducing the cross section and further increasing heat and evaporation of tungsten at these points      Sony VAIO PCG-6S3L Battery .

In small lamps operated on direct current, lifespan may be cut in half compared to AC operation. Different alloys of tungsten and rhenium can be used to counteract the effect  Sony VAIO PCG-6V1L Battery .

If a light bulb envelope leaks, the hot tungsten filament reacts with air, yielding an aerosol of brown tungsten nitride, brown tungsten dioxide, violet-blue tungsten pentoxide, and yellow tungsten trioxide which then deposits on the nearby surfaces or the bulb interiorSony VAIO PCG-6W1L Battery .

Bulb blackening

In a conventional lamp, the evaporated tungsten eventually condenses on the inner surface of the glass envelope, darkening it. For bulbs that contain a vacuum, the darkening is uniform across the entire surface of the envelope    Sony VAIO PCG-6W2L Battery .

When a filling of inert gas is used, the evaporated tungsten is carried in the thermal convection currents of the gas, depositing preferentially on the uppermost part of the envelope and blackening just that portion of the envelope     Sony VAIO PCG-6W3L Battery .

An incandescent lamp which gives 93% or less of its initial light output at 75% of its rated life is regarded as unsatisfactory, when tested according to IEC Publication 60064. Light loss is due to filament evaporation and bulb blackening. Study of the problem of bulb blackening led to the discovery of the Edison effect, thermionic emission and invention of the vacuum tube  Sony VAIO PCG-7111L Battery .

A very small amount of water vapor inside a light bulb can significantly affect lamp darkening. Water vapor dissociates into hydrogen and oxygen at the hot filament. The oxygen attacks the tungsten metal, and the resulting tungsten oxide particles travel to cooler parts of the lamp      Sony VAIO PCG-7112L Battery .

Hydrogen from water vapor reduces the oxide, reforming water vapor and continuing this water cycle. The equivalent of a drop of water distributed over 500,000 lamps will significantly increase darkening. Small amounts of substances such as zirconium are placed within the lamp as a getter to react with any oxygen that may bake out of the lamp components during operation  Sony VAIO PCG-7113L Battery .

Some old, high-powered lamps used in theater, projection, searchlight, and lighthouse service with heavy, sturdy filaments contained loose tungsten powder within the envelope. From time to time, the operator would remove the bulb and shake it  Sony VAIO PCG-7133L Battery ,

allowing the tungsten powder to scrub off most of the tungsten that had condensed on the interior of the envelope, removing the blackening and brightening the lamp again      Sony VAIO PCG-7Z1L Battery .

Halogen lamps

The halogen lamp reduces uneven evaporation of the filament and darkening of the envelope by filling the lamp with a halogen gas at low pressure, rather than an inert gas        Sony VAIO PCG-7Z2L Battery .

The halogen cycle increases the lifetime of the bulb and prevents its darkening by redepositing tungsten from the inside of the bulb back onto the filament. The halogen lamp can operate its filament at a higher temperature than a standard gas filled lamp of similar power without loss of operating life     Sony VAIO PCG-8Y1L Battery .

Incandescent arc lamps

A variation of the incandescent lamp did not use a hot wire filament, but instead used an arc struck on a spherical bead electrode to produce heat. The electrode then became incandescent, with the arc contributing little to the light produced      Sony VAIO PCG-8Y2L Battery .

Such lamps were used for projection or illumination for scientific instruments such as microscopes. These arc lamps ran on relatively low voltages and incorporated tungsten filaments to start ionization within the envelope. They provided the intense concentrated light of an arc lamp but were easier to operate       Sony VAIO PCG-8Z1L Battery .

Developed around 1915, these lamps were displaced by mercury andxenon arc lamps.

Electrical characteristics

Incandescent lamps are nearly pure resistive loads with a power factor of 1. This means the actual power consumed (in watts) and the apparent power (in volt-amperes) are equal       Sony VAIO PCG-8Z2L Battery .

The actual resistance of the filament is temperature-dependent. The cold resistance of tungsten-filament lamps is about 1/15 the hot-filament resistance when the lamp is operating. For example, a 100-watt, 120-volt lamp has a resistance of 144 ohms when lit, but the cold resistance is much lower (about 9.5 ohms)     Sony VGP-BPS21 Battery .

Since incandescent lamps are resistive loads, simple triac dimmers can be used to control brightness. Electrical contacts may carry a "T" rating symbol indicating that they are designed to control circuits with the high inrush current characteristic of tungsten lamps  Sony VGP-BPS21A Battery .

For a 100-watt, 120 volt general-service lamp, the current stabilizes in about 0.10 seconds, and the lamp reaches 90% of its full brightness after about 0.13 seconds.


Incandescent light bulbs are usually marketed according to the electrical power consumed    Sony VGP-BPS21B Battery .

This is measured in watts and depends mainly on theresistance of the filament, which in turn depends mainly on the filament's length, thickness, and material. For two bulbs of the same voltage, type, color, and clarity, the higher-powered bulb gives more light  Sony VGP-BPS21/S Battery .

The table shows the approximate typical output, in lumens, of standard incandescent light bulbs at various powers. Note that the lumen values for "soft white" bulbs will generally be slightly lower than for standard bulbs at the same power, while clear bulbs will usually emit a slightly brighter light than correspondingly powered standard bulbs      Sony VGP-BPS21A/B Battery .

Physical characteristics

Bulb shapes, sizes, and terms

Incandescent light bulbs come in a range of shapes and sizes. The names of the shapes may be slightly different in some regions. Many of these shapes have a designation consisting of one or more letters followed by one or more numbers, e.g. A55 or PAR38  SONY VGP-BPS21 Battery .

The letters represent the shape of the bulb. The numbers represent the maximum diameter, either in eighths of an inch, or in millimetres, depending on the shape and the region. For example, 63 mm reflectors are designated R63, but in the U.S. they are known as R20 (2.5 inches)     SONY VGP-BPS21A Battery .

However, in both regions, a PAR38 reflector is known as PAR38. In Australia an R80 is 1 inch in diameter.

Common shapes:

General Service

Light emitted in (nearly) all directions. Available either clear or frosted.

Types: General (A), Mushroom         SONY VGP-BPS21B Battery

High Wattage General Service

Lamps greater than 200 watts.

Types: Pear-shaped (PS)


lamps used in chandeliers, etc.

Types: candle (B), twisted candle, bent-tip candle (CA & BA), flame (F), fancy round (P), globe (G)  SONY VGP-BPS21/S Battery

Reflector (R)

Reflective coating inside the bulb directs light forward. Flood types (FL) spread light. Spot types (SP) concentrate the light. Reflector (R) bulbs put approximately double the amount of light (foot-candles) on the front central area as General Service (A) of same wattage      SONY VGP-BPS21A/B Battery .

Types: Standard reflector (R), elliptical reflector (ER), crown-silvered

Parabolic aluminized reflector (PAR)

Parabolic aluminized reflector (PAR) bulbs control light more precisely     WD passport essential (500GB/640GB) .

They produce about four times the concentrated light intensity of general service (A), and are used in recessed and track lighting. Weatherproof casings are available for outdoor spot and flood fixtures      WD passport essential (250GB/320GB) .

Available in numerous spot and flood beam spreads. Like all light bulbs, the number represents the diameter of the bulb in 1/8ths of an inch. Therefore, a PAR 16 is 2" in diameter, a PAR 20 is 2.5" in diameter, PAR 30 is 3.75" and a PAR 38 is 4.75" in diameter  WD  passport essential SE (750GB/1TB)        .

Multifaceted reflector (MR)


"HIR" is a GE designation for a lamp with an infrared reflective coating. Since less heat escapes, the filament burns hotter and more efficiently. The Osram designation for a similar coating is "IRC"   WD  passport elite(250GB/320GB) .

Lamp bases

Very small lamps may have the filament support wires extended through the base of the lamp, and can be directly soldered to a printed circuit board for connections. Some reflector-type lamps include screw terminals for connection of wires  WD passport elite(500GB/640GB) .

Most lamps have metal bases that fit in a socket to support the lamp and conduct current to the filament wires. In the late 19th century, manufacturers introduced a multitude of incompatible lamp bases. General Electric introduced standard base sizes for tungsten incandescent lamps under the Mazda trademark in 1909       WD  passport studio for Mac(320GB/500GB) .

This standard was soon adopted across the United States, and the Mazda name was used by many manufacturers under license through 1945. Today most incandescent lamps for general lighting service use an Edison screw in candelabra, intermediate, or standard or mogul sizes, or double contact bayonetbase        WD  passport studio for Mac(500GB/640GB) .

Bayonet base lamps are frequently used in automotive lamps to resist loosening due to vibration. A bipin base is often used for halogen or reflector lamps.

Lamp bases may be secured to the bulb with a cement, or by mechanical crimping to indentations molded into the glass bulb  WD  Elements series(250GB/320GB) .

Miniature lamps used for some automotive lamps or decorative lamps have wedge bases which have a partial plastic or even completely glass base. In this case, the wires wrap around to the outside of the bulb, where they press against the contacts in the socket. Miniature Christmas bulbs use a plastic wedge base as well      WD  Elements SE(500GB/640GB) .

Lamps intended for use in optical systems (such as film projectors, microscope illuminators, or stage lighting instruments have bases with alignment features so that the filament is positioned accurately within the optical system. A screw-base lamp may have a random orientation of the filament when the lamp is installed in the socket      WD Elements SE(750GB/1TB) .

Voltage, light output, and lifetime

See also: Lamp rerating

Incandescent lamps are very sensitive to changes in the supply voltage. These characteristics are of great practical and economic importance         WD  Elements desktop(500GB/640GB) .

For a supply voltage V near the rated voltage of the lamp:

  • Light output is approximately proportional to V 3.4
  • Power consumption is approximately proportional to V 1.6
  • Lifetime is approximately proportional to V ?16
  • Color temperature is approximately proportional to V 0.42 WD  Elements desktop(750GB/1TB)

This means that a 5% reduction in operating voltage will more than double the life of the bulb, at the expense of reducing its light output by about 20%. This may be a very acceptable trade off for a light bulb that is in a difficult-to-access location (for example, traffic lights or fixtures hung from high ceilings)         WD  Elements desktop(1.5 TB/2TB) .

Long-life bulbs take advantage of this trade-off. Since the value of

the electric power they consume is much more than the value of the lamp, general service lamps emphasize efficiency over long operating life. The objective is to minimize the cost of light, not the cost of lamps         WD  passport essential SE (750GB/1TB)--USB 3.0)       .

The relationships above are valid for only a few percent change of voltage around rated conditions, but they do indicate that a lamp operated at much lower than rated voltage could last for hundreds of times longer than at rated conditions, albeit with greatly reduced light output         WD  passport essential (500GB/640GB) .

The Centennial Light is a light bulb which is accepted by the Guinness Book of World Records as having been burning almost continuously at a fire station in Livermore, California, since 1901. However, the bulb is powered by only 4 watts. A similar story can be told of a 40-watt bulb in Texas which has been illuminated since September 21, 1908  WD  passport for Mac(320GB/500GB) .

It once resided in an opera house where notable celebrities stopped to take in its glow, but is now in an area museum.

In flood lamps used for photographic lighting, the tradeoff is made in the other direction   WD  passport for Mac(640GB/1TB) .

Compared to general-service bulbs, for the same power, these bulbs produce far more light, and (more importantly) light at a higher color temperature, at the expense of greatly reduced life (which may be as short as 2 hours for a type P1 lamp). The upper limit to the temperature at which metal incandescent bulbs can operate is the melting point of the metal      My book essential 4 generation  (640GB/1TB) .

Tungsten is the metal with the highest melting point, 3695 K (6192°F). A 50-hour-life projection bulb, for instance, is designed to operate only 50 °C (90 °F) below that melting point. Such a lamp may achieve up to 22 lumens per watt, compared with 17.5 for a 750-hour general service lamp      WD  My book essential 4 generation( 1.5TB/2TB) .

Lamps designed for different voltages have different luminous efficacy. For example, a 100-watt, 120-volt lamp will produce about 17.1 lumens per watt. A lamp with the same rated lifetime but designed for 230 V would produce only around 12.8 lumens per watt, and a similar lamp designed for 30 volts (train lighting) would produce as much as 19.8 lumens per watt  WD  My book elite( 1TB/1.5TB) .

Lower voltage lamps have a thicker filament, for the same power rating. They can run hotter for the same lifetime before the filament evaporates.

The wires used to support the filament make it mechanically stronger, but remove heat, creating another tradeoff between efficiency and long life   WD  My book studio(1TB/2TB) .

Many general-service 120-volt lamps use no additional support wires, but lamps designed for "rough service" or "vibration service" may have as many as five. Low-voltage lamps have filaments made of heavier wire and do not require additional support wires  WD  My book essential 4 generation( 1.5TB/2TB) .

Very low voltages are inefficient since the lead wires would conduct too much heat away from the filament, so the practical lower limit for incandescent lamps is 1.5 volts. Very long filaments for high voltages are fragile, and lamp bases become more difficult to insulate, so lamps for illumination are not made with rated voltages over 300 V       WD  My book elite(640GB/2TB) .

Some infrared heating elements are made for higher voltages, but these use tubular bulbs with widely separated terminals.

Health issues

Although some sources claim fluorescent lighting causes more health problems than incandescent lighting (see Light sensitivity and Over-illumination for discussion), more research needs to be done in this field  Seagate  expansion portable (320GB/500GB) .

According to the European Commission Scientific Committee on Emerging and Newly Identified Health Risks (SCENIHR) in 2008, the only property of compact fluorescent lamps that could pose an added health risk is the ultraviolet and blue light emitted by such devices      Seagate  expansion (1.5TB/2TB) .

The worst that can happen is that this radiation could aggravate symptoms in people who already suffer rare skin conditions that make them exceptionally sensitive to light. They also stated that more research is needed to establish whether compact fluorescent lamps constitute any higher risk than incandescent lamps    Toshiba  canvio for Mac(750GB/1TB) .

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