Incandescent light bulb 47139 225895484 2008-07-15T22:19:50Z User5910 4480889 /* Pin base */ Link to Bipin article The '''incandescent light bulb''', '''incandescent lamp''' or '''incandescent light globe''' is a source of artificial [[light]] that works by [[incandescence]], (a general term for heat-driven light emissions which includes the simple case of [[black body]] radiation). An [[electric current]] passes through a thin [[electrical filament|filament]], heating it until it produces light. The enclosing glass bulb prevents the [[oxygen]] in air from reaching the hot filament, which otherwise would be destroyed rapidly by oxidation. Incandescent bulbs are also sometimes called ''electric lamps'', a term also applied to the original [[arc lamp]]s. Incandescent bulbs are made in a wide range of sizes and [[voltage]]s, from 1.5 volts to about 300 volts. They require no external regulating equipment and have a low manufacturing cost, and work well on either alternating current or direct current. As a result the incandescent lamp is widely used in household and commercial lighting, for portable lighting, such as table lamps, some car [[headlamp]]s and electric [[flashlight]]s, and for decorative and advertising lighting. Some applications of the incandescent bulb make use of the heat generated, such as [[incubators]] (for hatching eggs), brooding boxes for young [[poultry]], heat lights for reptile [[terrarium|tanks]], [[Infrared heater|infrared heating]] for industrial heating and drying processes, and the [[Easy-Bake Oven]] toy. In cold weather the heat shed 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 ([[Compact fluorescent lamp|compact]]) [[fluorescent light]]s, [[high-intensity discharge lamp]]s, [[Light-emitting diode|LED]]s, and other devices, which give more visible light for the same amount of electrical energy input. Some jurisdictions are attempting to [[Banning of incandescent lightbulbs|ban the use of incandescent lightbulbs]] in favour of more energy-efficient lighting. ==History of the light bulb== [[Image:Edison Carbon Bulb.jpg|thumb|100px|left|Original carbon-filament bulb from [[Thomas Edison]]]] In addressing the question "Who invented the incandescent lamp?" historians Robert Friedel and Paul Israel <ref> Friedel, Robert, and Paul Israel. 1987. ''Edison's electric light: biography of an invention''. New Brunswick, New Jersey: Rutgers University Press. pages 115-117 </ref> list 22 inventors of incandescent lamps prior to Swan and Edison. They conclude that Edison's version was able to outstrip the others because of a combination of factors: an effective incandescent material, a higher vacuum than others were able to achieve and a high resistance lamp that made power distribution from a centralized source economically viable. 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, 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."<ref> Hughes, Thomas P. 1977. Edison's method. In ''Technology at the Turning Point'', edited by W. B. Pickett. San Francisco: San Francisco Press Inc., 5-22. </ref><ref> Hughes, Thomas P. 2004. ''American Genesis: A Century of Invention and Technological Enthusiasm''. 2nd ed. Chicago: The University of Chicago Press </ref> {| align="right" border="0" cellpadding="2" cellspacing="0" style="text-align:center; margin: 1em 1em 1em 1em;" |- !colspan="2" | Early evolution of the light bulb |- |colspan="2" | {{Early evolution of the light bulb}}<ref>{{cite book | last = Josephson | first = Matthew | title = Edison: a biography | publisher = McGraw Hill | date = 1959}} </ref> |- |} === Early pre-commercial research=== In 1802 [[Humphry Davy]] had what was then the most powerful [[Battery (electricity)|battery]] in the world at the [[Royal Institution]] of Great Britain. In that year, he created the first incandescent light by passing the current through a thin strip of platinum, 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 until [[Thomas Edison]]'s creation of the first commercially practical incandescent lamp in 1879.<ref name=Davis>Davis, L.J. "Fleet Fire." Arcade Publishing, New York, 2003. ISBN 1-55970-655-4</ref> In 1809, Davy created the first [[arc lamp]] by making a small but blinding electrical connection between two [[charcoal]] rods connected to a 2000 cell battery. It was demonstrated to the Royal Institution in 1810. In 1835, [[James 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". 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. In 1840, British scientist [[Warren de la Rue]] enclosed a platinum [[coil]] in a [[vacuum]] tube and passed an [[electric]] 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, improving its longevity. Although an efficient design, the cost of the platinum made it impractical for commercial use.<ref>{{cite web | last = | first = | title = The History Of The Light Bulb | publisher = Net Guides Publishing, Inc. | date = 2004 | url = http://www.thehistoryof.net/the-history-of-the-light-bulb.html | accessdate = 2007-05-02 }}</ref> <ref>{{cite web | last = | first = | title = The History of the light bulb | publisher = IN-VSEE | date = | url = http://invsee.asu.edu/Modules/lightbulb/meathist.htm | accessdate = 2007-05-02 }}</ref> In 1841, Frederick de Moleyns of England was granted the first patent for an incandescent lamp, with a design using powdered [[charcoal]] heated between two platinum wires contained within a vacuum bulb. In 1845, American John W. Starr acquired a patent for his incandescent light bulb involving the use of carbon filaments.<ref name=Derry&Williams> {{cite book | last = T.K. Derry & | first = Trevor Williams | title = A Short History of Technology | publisher = Oxford University Press | date = 1960 }}</ref> He died shortly after obtaining the patent. Aside from the information contained in the patent itself, little else is known about him. 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 Chateau of Blois. In 1872 [[Alexander Nikolayevich Lodygin|A. N. Lodygin]] invented an incandescent light bulb. In 1874 he obtained a patent for his invention. In a suit filed by rivals seeking to get around Edison's lightbulb patent, German-American inventor [[Heinrich Göbel]] claimed 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. [[Lewis Latimer]] demonstrated the bulbs Göbel had purportedly built in the 1850s had actually been built much later, and found the glassblower who had constructed the fraudulent exhibits.<ref name="Fouché">Fouché, Rayvon, ''Black Inventors in the Age of Segregation: Granville T. Woods, Lewis H. Latimer, and Shelby J. Davidson.'') (Johns Hopkins University Press, Baltimore & London, 2003, pp.115-116. ISBN 0-8018-7319-3</ref> In a patent interference suit in 1893, the judge ruled Göbel's claim "extremely improbable." [[Image:carbonfilament.jpg|thumb|Carbon filament lamp (E27 socket, 220 volts, approx. 30 watts, left side: running with 100 volts]] === Commercialization === [[Joseph Wilson Swan]] (1828–1914) was an English 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. 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, Swan developed a method of processing that avoided the early bulb blackening in 1878. This received a British Patent No 8 in 1880.<ref>Swan K R Sir Joseph Swan and the Invention of the Incandescent Electric Lamp. 1946 Longmans, Green and Co. Pp 21-25.</ref> On 18th 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 17th January 1879. It was also shown to 700 who attended a meeting of the Literary and Philosophical Society of Newcastle on 3rd February 1879. 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. Besides requiring too much current for a central station electric system to be practical, they had a very short lifetime.<ref>[http://americanhistory.si.edu/lighting/bios/swan.htm] "Lamp Inventors 1880-1940: Carbon Filament Incandescent" Smithsonian National Museum of American History. retrieved February 6, 2008</ref> 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.<ref> Swan K R Sir Joseph Swan and the Invention of the Incandescent Electric Lamp. 1946 Longmans, Green and Co. Pp 21-25.</ref> From this year he began installing light bulbs in homes and landmarks in England, and in the early 1880s he had started his company.<ref>R.C. Chirnside. Sir Joseph Wilson Swan FRS - The Literary and Philosophical Society of Newcastle upon Tyne 1979.</ref> In North America, parallel developments were also taking place. On [[July 24]] [[1874]] a [[Canada|Canadian]] [[patent]] was filed for the Woodward and Evans Light by a [[Toronto]] medical electrician named [[Henry Woodward (inventor)|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]]. Woodward and Evans attempted to commercialize their lamp, but were unsuccessful. They ended up selling their patent ({{US patent|0181,613}}) to Thomas Edison in 1879 [http://www.physics.uoguelph.ca/summer/scor/articles/scor18.htm]. [[Thomas Edison]] began serious research into developing a practical incandescent lamp in 1878. Edison filed his first patent application for "Improvement In Electric Lights" on October 14, 1878 ({{US patent|0214636}}). After many experiments with platinum and other metal filaments, Edison returned to a [[carbon]] filament. The first successful test was on [[October 22]] [[1879]];<ref>Paul Israel, ''Edison: a Life of Invention'', Wiley (1998), page 186.</ref> and lasted 13.5 hours. Edison continued to improve this design and by Nov 4, 1879, filed for a U.S. patent (granted as {{US patent|0223898}} on Jan 27, 1880) for an electric lamp using "a carbon filament or strip coiled and connected ... to platina contact wires."<ref name=Patent898> {{US patent|0223898}}</ref> Although the patent described several ways of creating the carbon filament including using "cotton and linen thread, wood splints, papers coiled in various ways,"<ref name="Patent898"/> 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. His United States Electric Lighting Company was the second company to sell practical incandescent electric lamps, after Edison. 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. Maxim in October 1880 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. 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.<ref name="Fouché"/> In Britain, the Edison and Swan companies merged into the Edison and Swan United Electric Company (later known as [[Joseph Swan#Ediswan|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. 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. Swan later wrote that Edison had a greater claim to the light than he did, in order to protect Edison's patents from claims against them in the US. [[Image:Light bulb.png|thumb|left|280px|{{US patent|0223898}} by [[Thomas Edison]] for an improved electric lamp, [[January 27]] [[1880]]]] In 1882 the first recorded set of [[Christmas lights|miniature incandescent lamps]] for lighting a [[Christmas tree]] was installed. These did not become common in homes for many years. The [[United States Patent and Trademark Office|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. 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. In the 1890s, the Austrian inventor [[Carl Auer von Welsbach]] worked on metal-filament mantles, first with [[platinum]] wiring, and then [[osmium]], and produced an operative version in 1898. 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. In 1903, Willis Whitnew invented a filament that would not blacken the inside of a light bulb. (Some of Edison's experiments to stop this blackening led to the invention of the [[electronics|electronic]] [[vacuum tube]].) It was a metal-coated carbon filament. On December 13th 1904, Sándor Just and [[Franjo Hannaman|Ferenc 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. 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.<ref>{{cite web | last = | first = | title = The History of Tungsram | publisher = | date = | url = http://www.tungsram.hu/tungsram/downloads/tungsram/tu_short_history_1896-1996.pdf | accessdate = }}</ref> In 1906, the [[General Electric|General Electric Company]] patented a method of making [[tungsten]] filaments for use in incandescent light bulbs. [[Sinter]]ed tungsten filaments were costly, but by 1910 [[William David Coolidge]] (1873–1975) had invented an improved method of making tungsten filaments. The tungsten filament outlasted all other types of filaments and Coolidge made the costs practical. 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. [[Marvin Pipkin]], an American chemist, in 1924 patented a process for frosting the inside of lamp bulbs without weakening them, and in 1947 patented a process for coating the inside of lamps with [[silica]]. In 1936 the coiled-coil filament was introduced which further improved the efficiency of lamps. <ref> ''Incandescent Lamps publication TP-110'', General Electric, Nela Park, 1964 , page 3 </ref> 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 <ref> General Electric TP-110 pg. 3 </ref> ===Cartels=== {{main|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. ==Construction== Incandescent light bulbs consist of a [[glass]] enclosure (the envelope, or bulb) which is filled with an [[inert gas]] to reduce evaporation of the filament. Inside the bulb is a [[electrical filament|filament]] of [[tungsten]] wire, through which an [[electric current]] is passed. The current heats the filament to an extremely high temperature (typically 2000 K to 3300 K depending on the filament type, shape, size, and amount of current passed through). The heated filament emits light that approximates a [[black body|continuous spectrum]]. The useful part of the emitted energy is [[visible light]], but most energy is given off in the near-[[infrared]] wavelengths. {| border="0" | [[Image:Incandescent light bulb.svg|300px|center]] | #Outline of Glass bulb #Low pressure inert gas(argon, neon, nitrogen) #Tungsten filament #Contact wire (goes out of stem) #Contact wire (goes into stem) #Support wires #Stem (Glass mount) #Contact wire (goes out of stem) #Cap (Sleeve) #Insulation (Vitrite) #Electrical contact |} Incandescent light bulbs usually contain a glass mount, which supports the filament lead wires and allows the electrical contacts to run through the envelope without gas/air leaks. 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. 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 range from about 0.1 [[watt]] to about 10,000 watts. To improve the efficacy of the lamp, the filament usually consists of coils of fine wire, also known as a 'coiled coil'. For a 60 watt 120-volt lamp, the uncoiled length of the filament is usually 22.8 inches or 580 mm <ref> General Electric TP-110, page 22</ref> and the filament diameter is 0.0018 inches (0.045 mm). One of the problems of the standard electric light bulb is evaporation of the filament. Small variations in [[electrical resistivity|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 <ref> General Electric TP-110 page 7</ref>. The hot spots evaporate faster than the rest of the filament, increasing resistance at that point&mdash;a [[positive feedback]] which ends in the familiar tiny gap in an otherwise healthy-looking filament. [[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]],<ref> John Kaufman (ed.), ''IES Lighting Handbook 1981 Reference Volume'', Illuminating Engineering Society of North America, New York, 1981 ISBN 0-87995-007-2 page 8-6 </ref> or [[krypton]]<ref> Burgin. Lighting Research and Technology 1984 16.2 61-72</ref>. However, a filament breaking in a gas-filled bulb can form an [[electric arc]], which may spread between the terminals and cause very heavy current; intentionally thin lead-in wires or more elaborate protection devices are therefore often used as [[fuse (electrical)|fuses]] built into the light bulb. <ref>{{cite web | last = Robert | first = Hunt | title = Glass Blowing for Vacuum Devices - Lamp Autopsy | publisher = Teralab | date = 2001-2006 | url = http://www.teralab.co.uk/Glass_Blowing/Lamp_Autopsy/Lamp_Autopsy_Page1.htm | accessdate = 2007-05-02 }}</ref> More nitrogen is used in higher-voltage lamps to reduce the possibility of arcing. 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 2000 hours for lamps used for general illumination. 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. 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. 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. 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. <ref> IEC 60064 Tungsten filament lamps for domestic and similar general lighting purposes. </ref>) ''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. 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. <ref> [http://www.toshiba-lighting.com/servlet/ShowInfoSR?M=S97SFR11RFK1KFL1LF Toshiba Lighting Products Miniature Lamp Characteristics], retrieved 2008 March 23 </ref> <ref> John Kaufman (ed.), ''IES Lighting Handbook 1981 Reference Volume'', Illuminating Engineering Society of North America, New York, 1981 ISBN 0-87995-007-2 page 8-9 </ref> A very small amount of water vapor 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. 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. <ref> General Electric manual TP 110 </ref> In a [[halogen lamp]] uneven evaporation of the filament and darkening of the envelope is reduced by filling the lamp with a [[halogen]] gas at low pressure. These lamps can operate at a higher filament temperature without unacceptable loss of life, giving them a higher luminous efficiency. 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, 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. <ref> John Kaufman (ed.), ''IES Lighting Handbook 1981 Reference Volume'', Illuminating Engineering Society of North America, New York, 1981 ISBN 0-87995-007-2 page 8-10 </ref> If a light bulb envelope leaks, the hot tungsten filament reacts with the 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 interior.<ref>{{cite web | last = Hochgraf | first = Fredrick G. | title = Review of Lamp Examination for ON or OFF in Traffic Accidents | publisher = Northwestern University Traffic Institute | date = 1985 | url = http://mfes.com/lamps.htm | accessdate = 2007-05-02 }}</ref> The glass bulb of a general service lamp can reach temperatures between 400 and 550 degrees Fahrenheit (200 to 260 degrees Celsius). Lamps intended for high power operation or used for heating purposes will have envelopes made of hard glass or fused quartz. <ref> General Electric TP-110 page 26 </ref> ===Incandescent arc lamp=== A variation of the incandescent lamp did not use a heated filament of wire to produce light but instead used an arc struck between bead-shaped electrodes to produce heat; the electrodes then became incandescent, with the arc contributing little to the light produced. Such lamps were used for projection or illumination for scientific instruments. 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. Developed around 1915, these lamps were displaced by mercury and xenon arc lamps. <ref> http://www.lamptech.co.uk/Miscellaneous.htm Incandescent arc lamps retrieved June 16, 2008 </ref> ==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-ampere]]s) are equal. The actual resistance of the filament is temperature dependent. The cold resistance of tungsten filament lamps is about 1/15 the resistance when the lamp is lit. For example, a 100 watt, 120 volt lamp has a resistance of 144 Ω when lit, but the cold resistance is much lower (about 9.5 ohms) <ref> General Electric TP-110 page 24 </ref> <ref> Edison's research team was aware of the large negative temperature coefficient of resistance of possible lamp filament materials and worked extensively during the period 1878-1879 on devising an automatic regulator or ''ballast'' to stabilize current. It wasn't until 1879 that it was realized a self-limiting lamp could be built. See Friedel and Israel ''Edison's Electric Light'' pages 29-31 </ref>. Since incandescent lamps are resistive loads, simple [[thyristor|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. 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. <ref> General Electric TP-110 page 23, 24</ref> ===Power=== {| class="wikitable" | align="right" |+ Comparison of efficacy by power (120 Volt lamps) !Power ([[Watt|W]])||Output ([[lumen (unit)|lm]])||Efficacy (lm/W) |- |5 |25 |5 |- |15 |110 |7.3 |- |25 |200 |8.0 |- |35 |350 |10.3 |- |40 |500 |12.5 |- |50 |700 |13.5 |- |55 |800 |14.2 |- |60 |850 |14.5 |- |65 |1000 |15.0 |- |70 |1100 |15.7 |- |75 |1200 |16.0 |- |90 |1450 |16.1 |- |95 |1600 |16.8 |- |100 |1700 |17.0 |- |135 |2350 |17.4 |- |150 |2850 |19.0 |- |200 |3900 |19.5 |- |300 |6200 |20.7 |} Incandescent light bulbs are usually [[marketing|marketed]] according to the [[electric power|electrical power]] consumed. This is measured in [[watt]]s and depends mainly on the [[electrical resistance|resistance]] 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. 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. ===Comparison of electricity cost=== The [[watt-hour|kilowatt-hour]], is the usual unit of electrical energy purchase. The cost of electricity in the United States normally ranges from $0.06 to $0.18 per kilowatt-hour (kWh), but can be as high as $0.23 per kWh in certain areas such as [[Hawaii]]. As for any other electrical appliance, the hourly cost of operation can be calculated by multiplying the input in watts by the cost per kilowatt-hour and divding by 1000; for example, a 100-watt lamp operated on electricity that costs 10 cents per kilowatt-hour will cost 100 * 10/1000 = 1 cent per hour to operate. The desired product of any electric lighting system is illumination (lumens), not power. To compare incandescent lamp operating cost with other light sources, the calculation must also consider the lumens produced by each lamp. For commercial and industrial lighting systems the comparison must also include the required illumination level, effectiveness of the lighting fixtures, the capital cost of the lamp, the labor cost to replace lamps, the various depreciation factors for light output as the lamp ages, effect of lamp operation on heating and air conditioning systems, and also the energy consumption. Overall cost of lighting must also take into account light lost within the lamp holder fixture; internal reflectors and updated design of lighting fixtures can improve the amount of usable light delivered. Since human vision adapts to a wide range of light levels, a 10% or 20% decrease in lumens may still provide acceptable illumination, especially if the changeover is accompanied by cleaning of lighting equipment or improvements in fixtures. ==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, PAR38. The letters represent the shape of the bulb. The numbers represent the maximum diameter, either in eights of an inch, or in milimetres, depending on the shape and the region. For example, in Europe, Australia and elsewhere, 63mm reflectors are known as R63, whereas in the US they are known as R20 (2.5 inches). However, in both regions, a PAR38 reflector is known as PAR38. These designations may also apply to non incandescent lamps. For example, compact fluorescent lamps. Common shapes: ;General Service :Light emitted in all directions. Available in either clear or frosted. :Types: General (A), Mushroom ;High Wattage General Service :Lamps greater than 200 watts. :Types: Pear-shaped (PS) ;Decorative :lamps used in chandeliers, etc. :Types: Candle(B), Twisted Candle, Bent-tip Candle (CA & BA), Flame (F), Fancy Round(P), Globe(G) ;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. :Types: Standard Reflector(R), Elliptical Reflector (ER), Crown Silvered ;Parabolic Aluminized Reflector (PAR): Parabolic Aluminized Reflector (PAR) bulbs control light more precisely. 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. :120V Sizes:PAR 16, 20, 30 and 38 :230V Sizes:Par 38 & 56 :Available in numerous spot and flood beam spreads. Like all light bulbs, the number represents the diameter of the bulb in 1/8s 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. ;Multifaceted Reflector (MR) ;HIR: "HIR" means that the bulb has a special coating that reflects infrared back onto the filament. Therefore, less heat escapes, so the filament burns hotter and more efficiently.<ref>[http://www.gelighting.com/na/business_lighting/education_resources/glossary.htm Lighting Glossary]</ref> ===Standard fittings=== [[Image:Gluehlampe 01 KMJ.png|right|thumb|100px|A light bulb with a standard E27 Edison screw base]] [[Image:BCincandescentlamp.jpg|right|thumb|100px|The double-contact bayonet cap on an incandescent bulb]] Most domestic and industrial light bulbs have a metal fitting (or lamp base) compatible with standard sockets. [[General Electric]] introduced standard base sizes for tungsten incandescent lamps under the [[Mazda (light bulb)|Mazda]] trademark in 1909. This standard was soon adopted across the United States, and the Mazda name was used by many manufacturers under license through 1945. ====Screw thread==== {{main|Edison screw}} In each designation, the E stands for Edison, who created the screw-base lamp, and the number is the [[diameter]] of the screw base in millimeters. (This is even true in North America, where designations for the bulb glass diameter are in eighths of an [[inch]].) There are four common sizes of screw-in sockets used for line-voltage lamps: *[[candelabra]]: E12 North America, E10 & E11 in Europe *intermediate: E17 North America, E14 (SmallES) in Europe *medium or standard: E26 (MES) in North America, E27 (ES) in Europe *mogul: E39 North America, E40 (GoliathES) in Europe. Other screw thread sizes include: *"admedium" size (E29), larger than common lamp sockets, intended to frustrate thieves of bulbs used in public places; * miniature size (E5) generally used only for low-voltage applications such as with a [[battery (electricity)|battery]]. The largest size E39 is used on large [[street light]]s, and high-wattage lamps (such as a 100/200/300-watt three-way) and many non-incandescent high-intensity discharge bulbs. Medium Edison screw (MES) bulbs for 12 volts are also produced for [[recreational vehicle]]s. Large outdoor Christmas lights use an intermediate base, as do some desk lamps and many [[microwave oven]]s. Formerly [[Emergency exit]] signs also tended to use the intermediate base (but US and Canadian rules now require more energy-efficient lamps). A medium screw base should not carry more than 25 amperes current; this may limit the practical rating of low-voltage lamps. <ref> General Electric TP 110 page 12 </ref> ====Bayonet==== Bulbs with a bayonet (push-twist) base for use with sockets having spring-loaded base plates, are produced in similar sizes and are given a B, BA or BY designation. These are also common in 12-volt [[automobile lighting]] worldwide, in addition to [[wedge]]-base lamps 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. <br /><br />BC or B22 or B22d or double-contact [[Bayonet mount|bayonet cap]] are used in the UK, Ireland, Australia, India, New Zealand and the various parts of the British Commonwealth for most 220–240 V mains lamps. A smaller version, the B15 or SBC, is sometimes used for candle bulbs for chandeliers. A miniature bayonet is used in North America for appliances such as [[sewing machine]]s and [[vacuum cleaner]]s. <br /> <br />These are the available sizes in the UK:<ref>see http://technical.greenstock.co.uk/KYBLampBases.htm</ref> {| class="wikitable" |- ! designation ! alternative designation ! dimension, etc. |- | Ba5s | | 5mm |- | Ba7s | | 7 mm |- | Bax9s | | 9mm |- | Ba9s | MBC | 9mm Miniature Bayonet Cap |- | Ba15d | SBC | 15mm Small Bayonet Cap |- | Bax15s | | 15mm |- | Ba15s | SCC | 15mm Single Centre Contact |- | Ba20s | | 20mm |- | Ba20d | | 20mm |- | Ba21d | | 21mm |- | B21-4 | | 21mm 4 Pin |- | Ba22d | BC | 22mm Bayonet Cap |- | BC-3 | BC3 | 22mm Bayonet Cap 3 Pin |- | B22d-3 | | 22mm Double Ended (Railway) |- | Bx22d | | 22mm |} Of these, only the BC or the Ba22d is commonly sold in supermarkets. ====Pin base==== A pin base, has two contacts on the underside of the bulb (see [[bipin]] entry). These are given a G or GY designation, with the number being the center-to-center distance in millimeters. For example, a 4 mm pin base would be indicated as G4 (or GY4). Some common sizes include G4 (4 mm), G6.35 (6.35 mm), G8 (8 mm), GY8.6 (8.6 mm), G9 (9 mm), and GY9.5 (9.5 mm). The second letter (or lack thereof) indicates pin diameter. Some [[Stage lighting instrument#Spotlights|spotlights]] or [[Stage lighting instrument#Floodlights|floodlights]] have pins that are broader at the tips, in order to lock into a socket with a twist. Other lamps come in a tube, with blades or dimples at either end. ====Special lamp bases==== There are also special bases for [[projector]]s and [[stage lighting instrument]]s. Projector lamps<ref name="PartStore">[http://www.partstore.com/MiniSites/ProjectorLamps/DefaultInfo.aspx The Basics About Projector Lamps]. Published by [[PartStore]], accessed on June 29, 2007.</ref>, in particular, may run on unusual voltages (such as 82), perhaps intended as a [[vendor lock-in]] or to optimize light output for a particular optical system. Lamps intended for use in optical systems (such as film projectors, microscope illuminators, or theatrical 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. Tubular lamps such as R7S-75 for halogen lamp tubes, in this case a 7 mm diameter socket with 75 mm tube length.<ref>{{cite web|title=butiken.su.se Stockholms universitet|url=http://www.butiken.su.se/katalog.php?kat=6}}"MT0414 Lampa, halogen, 300W, R7s-15 Haloline" / see picture</ref> ==Voltage, light output, and lifetime== {{Seealso|Lamp rerating}} Incandescent lamps are very sensitive to changes in the supply voltage. These characteristics are of great practical and economic importance. For a supply voltage ''V'', *''Light'' output is approximately proportional to ''V''<sup> 3.4</sup> *''Power'' consumption is approximately proportional to ''V''<sup> 1.6</sup> *''Lifetime'' is approximately ''inversely'' proportional to ''V''<sup> 16</sup> *''Color temperature'' is approximately proportional to ''V''<sup> 0.42</sup> <ref> Donald G. Fink and H. Wayne Beaty, ''Standard Handbook for Electrical Engineers, Eleventh Edition'',McGraw-Hill, New York, 1978, ISBN 0-07020974-X, pg 22-8 </ref> 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). So-called "long-life" bulbs are simply bulbs that 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 for illumination usually emphasize efficiency over long operating life; the objective is to minimize the cost of light, not the cost of lamps. <ref> General Electric TP-110, page 20 </ref> 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. 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]]. It once resided in an [[opera house]] where notable celebrities stopped to take in its glow, but is now in an area [[museum]].<ref>[http://www.homelighting.com/article.cfm?intarticleID=880 Magazine Online<!-- Bot generated title -->]</ref> In flood lamps used for [[photography|photographic]] lighting, the trade-off is made in the other direction. 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. Tungsten is the metal with the highest melting point. A 50-hour-life projection bulb, for instance, is designed to operate only 50 [[Celsius|°C]] (90 [[Fahrenheit|°F]]) below that melting point. Such a lamp may achieve up to 22 lumens/watt , compared with 17.5 for a 750-hour general service lamp. <ref> General Electric TP-110, page 19 </ref> 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/watt, and a similar lamp designed for 30 volts (train lighting) would produce as much as 19.8 lumens/watt. <ref> General Elecric TP 110 pg. 19 </ref> Lamps also vary in the number of support wires used for the tungsten filament. Each additional support wire makes the filament mechanically stronger, but removes heat from the filament, creating another trade-off between efficiency and long life. Many modern general service 120 volt lamps use no additional support wires, but lamps designed for "rough service" often have several support wires and lamps designed for "vibration service" may have as many as five. Lamps designed for low voltages (for example, 12 volts) generally have filaments made of much heavier wire and do not require any additional support wires. Very low voltages are inefficient since the lead wires would conduct too much heat away from the filament, so the practical lower limit 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. <ref> General Electric TP 110 </ref> Some infrared heating elements are made for higher voltages, but these use tubular bulbs with widely-separated terminals. == Luminous efficacy and efficiency == [[Image:Tungsten filament in halogen lamp.JPG|thumb|Close-up of a tungsten filament inside a halogen lamp. The two ring-shaped structures left and right are filament supports.]] Approximately 90% of the power consumed by an incandescent light bulb is emitted as [[heat]], rather than as visible [[light]]. <ref> General Electric TP-110, page 23, table. </ref> [[Luminous efficacy]] is a ratio of the visible light energy emitted ( the ''luminous flux'') to the total power input to the lamp. It is measured in [[lumen (unit)|lumen]]s per [[watt]] (lm/W). The maximum efficacy possible is 683&nbsp;lm/W for monochromatic green light at 555 nanometres wavelength, the peak sensitivity of the human eye. For white light, the maximum luminous efficacy is around 240 lumens/watt. Luminous ''efficiency'' is the ratio of the luminous ''efficacy'' to this maximum possible value. It is expressed as a number between 0 and 1, or as a percentage.<ref>http://www.iupac.org/publications/analytical_compendium/Cha10sec21.pdf</ref> However, the term ''luminous efficiency'' is often used for both quantities. Two related measures are the ''overall luminous efficacy'' and ''overall luminous efficiency'', which divide by the total power input rather than the total radiant flux. This takes into account more ways that energy might be wasted and so they are never greater than the standard luminous efficacy and efficiency. The term "luminous efficiency" is often misused, and in practice can refer to any of these four measures. 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#Overall luminous efficacy|luminous efficacy]] compares a broader array of light sources to one another. {| class="wikitable" !Type||Overall luminous efficiency||Overall luminous efficacy (lm/W) |- |40 W tungsten incandescent |1.9% |12.6<ref name="incandescent">{{cite web | title=The Nature of Light| last=Keefe| first=T.J.| year=2007| url=http://www.ccri.edu/physics/keefe/light.htm | accessdate=2007-11-05}}</ref> |- |60 W tungsten incandescent |2.1% |14.5<ref name="incandescent"/> |- |100 W tungsten incandescent |2.6% |17.5<ref name="incandescent"/> |- |glass halogen |2.3% |16 |- |quartz halogen |3.5% |24 |- |high-temperature incandescent |5.1% |35<ref name="bulbguide">{{cite web | author=Klipstein, Donald L.| year=1996 | title=The Great Internet Light Bulb Book, Part I | url=http://freespace.virgin.net/tom.baldwin/bulbguide.html | accessdate=2006-04-16}}</ref> |- |ideal [[black-body]] radiator at 4000&nbsp;K |7.0% |47.5<ref name="blackbody">[[:De:Bild:Blackbodyvisiblerp.png|Black body visible spectrum]]</ref> |- |ideal black-body radiator at 7000&nbsp;K |14% |95<ref name="blackbody"/> |- |ideal white light source |35.5% |242.5<ref name="bulbguide"/> |- |ideal monochromatic 555&nbsp;nm (green) source |100% |683<ref name="luminosity">See [[luminosity function]].</ref> |} A 100 W bulb for 120 V systems, produces 17.5 lm/W, compared to a theoretical "ideal" of 242.5 lm/W for white light. Unfortunately, tungsten filaments radiate mostly infrared radiation at temperatures where they remain [[solid]] (below 3683 [[kelvin]]s). Donald L. Klipstein explains it this way: "An ideal thermal radiator produces visible light most efficiently at temperatures around 6300 °C (6600&nbsp;K or 11&thinsp;500&nbsp;°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."<ref name="bulbguide"/> No known material can be used as a filament at this ideal temperature, which is hotter than the sun's surface. The spectrum emitted by a [[blackbody]] radiator does not match the sensitivity characteristics of the human eye. An upper limit for incandescent lamp luminous efficacy is around 52 lumens per watt, the theoretical value emitted by tungsten at its melting point. <ref> General Electric TP-110 page 19 </ref> 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. <ref>Prof. Peter Lund, Helsinki University of Technology,[http://www.tkk.fi/Units/AES/staff/lund.htm] on p. C5 in [[Helsingin Sanomat]] Oct. 23, 2007.</ref> Quality [[halogen lamp|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, the 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. Alternatives to standard incandescent lamps for general lighting purposes include: *[[Fluorescent lamp]]s, and [[Compact fluorescent lamp]]s *[[High-intensity discharge lamp]]s *[[LED lamps]] None of these devices rely on incandescence to produce light. Instead, all these devices produce light by the transition of electrons from one energy level to another. These mechanisms produce discrete [[spectral line]]s and so are not associated with the broad "tail" of invisible infrared emissions produced by incandescent emitters, which is energy not usable for illumination. 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 temperature]]s of white for visible light. == Laws and regulations to discontinue use == {{main|Banning of incandescent lightbulbs}} Due to the higher energy usage of incandescent light bulbs in comparison to more energy efficient alternatives, like [[compact fluorescent lamp]]s and [[LED lamp]]s, some governments have passed laws and regulations that have started to phase out their usage. [[Brazil]] and [[Venezuela]] started to phase them out in 2005, and other nations are planning scheduled phase-outs: [[Ireland]] in 2009, [[Australia]] in 2010, [[Canada]] in 2012, and the U.S. between 2012 and 2014. Most of these laws and regulations do not ban the usage of incandescents, but rather ban their sale. ===Efforts to improve efficiency=== Various efforts to improve the efficiency of incandescent lamps have been made recently, due to legislation and other movements to [[Banning of incandescent lightbulbs|ban incandescent lamps]]. The consumer lighting division of [[General Electric]] has announced that they are working on what they have dubbed "high efficiency incandescent" (HEI) lamps, which are ultimately expected to be four times as efficient as current incandescent lamps, although their initial production goal is to be 30 lumens per watt or twice as efficient. <ref>{{Citation | last = Daley | first = Dan | title = Incandescent's Not-So-Dim Future | newspaper = Projection Lights and Staging News (PLSN) | volume = 09 | issue = 1 | pages = 46 | publisher = Timeless Communications Corp. | year = 2008 | date = February 2008}}</ref><ref>[http://www.businesswire.com/portal/site/ge/index.jsp?ndmViewId=news_view&newsId=20070223005120 GE Announces Advancement in Incandescent Technology; New High-Efficiency Lamps Targeted for Market by 2010]</ref> In 2006, David Cunningham, who has produced many innovations in [[Stage lighting|entertainment lighting]], filed for a US Patent for a lamp using an infrared reflector. <ref>{{Citation | last = Cunningham | first = David | title = Incandescent lamp incorporating extended high-reflectivity IR coating and lighting fixture incorporating such an incandescent lamp (United States Patent 20060226777) | year = 2006}}</ref> The US Department of Energy at [[Sandia National Laboratories]] is also currently developing a filament lamp with improved efficiency from 5% to 60%.<ref>{{Citation | title = Proposed Bulb Ban Causes Chain Reaction | newspaper = Projection Lights and Staging News (PLSN) Online | year = 2008 | date = January 2008 | url = http://www.plsn.com/index.php?option=com_content&task=view&id=1606&Itemid=41}}</ref><ref>{{Citation | last = Daley | first = Dan | title = Incandescent's Not-So-Dim Future | newspaper = Projection Lights and Staging News (PLSN) | volume = 09 | issue = 1 | pages = 46 | publisher = Timeless Communications Corp. | year = 2008 | date = February 2008}}</ref> ==See also== {{portal|Energy}} <div style="-moz-column-count:3; column-count:3;"> * [[Centennial Light]] * [[Fluorescent lamp]] * [[Lightbulb joke]]s * [[Longest-lasting light bulbs]] * [[Light-emitting diode]] (LED) * [[Light fixture]] * [[LED lamp]] * [[List of light sources]] * [[Luminous efficacy]] * [[MR16]] (a popular style of halogen lamp) * [[Over-illumination]] * [[Photometry (optics)]] Main Photometry/Radiometry article - explains technical terms * [[Spectrometer]] * [[Thomas Edison]] </div> ==References== {{Reflist|2}} ==External links== {{Commonscat|Incandescent light bulb}} * [http://science.howstuffworks.com/light-bulb2.htm Howstuffworks - "How Light Bulbs Work"] * [http://www.graphics.cornell.edu/online/measurements/source-spectra/index.html Light Source Spectra] 60W-100W Incandescent light bulb spectra * [http://bulbster.com/lightbulbs/singleended-halogen-c-783_43230.html Light Bulb Base Identification] * [http://www.thelightbulb.co.uk/faq_bases.php Light Bulbs - Lamps and Tubes - Lamp Bases Explained] * [http://www.juliantrubin.com/bigten/bulbexperiment.html The Perfection of the Electric Light Bulb] - background and experiment {{ArtificialLightSources}} [[Category:Incandescent light bulbs| ]] [[Category:English inventions]] [[Category:Thomas Edison]] [[Category:Discovery and invention controversies]] [[Category:Recyclable materials]] <!-- interwiki --> [[bg:Лампа с нажежаема жичка]] [[bs:Sijalica]] [[ca:Bombeta elèctrica]] [[cs:Žárovka]] [[da:Glødelampe]] [[de:Glühlampe]] [[et:Hõõglamp]] [[el:Λαμπτήρας]] [[es:Lámpara incandescente]] [[eo:Ampolo]] [[eu:Bonbilla]] [[fr:Lampe à incandescence classique]] [[fy:Gloeilampe]] [[gd:Bolgan (innleachd)]] [[ko:백열등]] [[id:Lampu pijar]] [[is:Ljósapera]] [[it:Lampadina]] [[he:נורה חשמלית]] [[ka:ნათურა]] [[lt:Kaitrinė lemputė]] [[hu:Izzólámpa]] [[ms:Mentol lampu]] [[nl:Gloeilamp]] [[ja:電球]] [[no:Glødelampe]] [[nn:Glødelampe]] [[pl:Żarówka]] [[pt:Lâmpada incandescente]] [[ksh:Bier (en de Lamp)]] [[ru:Лампа накаливания]] [[simple:Lightbulb]] [[sk:Žiarovka]] [[fi:Hehkulamppu]] [[sv:Glödlampa]] [[ta:வெள்ளொளிர்வு விளக்கு]] [[tr:Ampul]] [[zh:電燈泡]]