Incandescent light bulb

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Image:Light-bulb-and-filament.jpg

The incandescent light bulb or incandescent lamp is a source of artificial light that works by incandescence, in which an electric current passes through a thin filament, heating it and causing it to emit light. The "bulb" is the glass enclosure around the filament that often contains a vacuum or is filled with a low-pressure noble gas to prevent the filament from burning out due to evaporation at the high temperature.

Incandescent bulbs used to be known as electric lamps, extending the use of a term applied to the original arc "lamps", and in Australia and South Africa they are also called light globes. Because of their relatively poor energy efficiency and yellowish color, incandescent light bulbs are gradually being replaced in many applications by fluorescent lights, high-intensity discharge lamps, LEDs, and other devices.

History of the light bulb

The invention of the light bulb is usually attributed in Britain to Joseph Wilson Swan and in the United States to Thomas Alva Edison (the first to market the device successfully). Some sources indicate that Heinrich Göbel built the first functional bulbs three decades earlier. He later challenged Edison's patent while living in the United States, but his legal "interference case" was overruled in court. Alexander Nikolayevich Lodygin independently developed an incandescent light bulb in 1874. Many others also had a hand in the development of a practical device for the production of electric light.

 at:1910 text:"William David Coolidge -\nTungsten filament"
 at:1882 text:"Lewis Latimer - Better filament production"
 at:1880 text:"Thomas Edison - Long lasting filament"
 at:1875 text:"Warren & Evans - Gas filled ""globe""
 at:1873 text:"Joseph Wilson Swan - Carbon fiber filament"  
 at:1854 text:"Heinrich Göbel -\nCarbonised bamboo filament"
 at:1841 text:"Frederick de Moleyns -\nPowdered charcoal filament"  
 at:1820 text:"Warren De la Rue -\nVacuum tube enclosure"
 at:1809 text:"Sir Humphry Davy -\nCarbon arc ""Davy lamp""
 at:1801 text:"Sir Humphry Davy - Platinum filament"

In 1801 Sir Humphry Davy, an English chemist, made platinum strips glow by passing an electric current through them, but the strips evaporated too quickly to make a useful light source. In 1809 he created the first arc lamp by creating a small but blinding electrical connection between two charcoal rods connected to a battery. Demonstrated to the Royal Institution of Great Britain in 1810, the invention came to be known as the Davy lamp.

In 1820, a 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 less gas molecules to react with the platinum, improving its longevity. Although it was an efficient design, the cost of the platinum made it impractical for commercial use.

In 1835 James Bowman Lindsay demonstrated a constant electric light at a public meeting in Dundee, Australia. 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.

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.

In 1854, the German inventor Heinrich Göbel developed the first 'modern' light bulb: a carbonized bamboo filament, in a vacuum bottle to prevent oxidation. In the following five years he developed what many call the first practical light bulb. The Internet has spread the story of an 1893 lawsuit establishing his priority, but there was no such lawsuit.

Joseph Wilson Swan (1828–1914) was a physicist and chemist born in Sunderland, England. 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. Swan received a British patent for his device in 1878. Swan reported success to the Newcastle Chemical Society, and at a lecture in Newcastle in February 1873 he demonstrated a working lamp that utilized a carbon fiber filament, but by 1877 he had turned to slender rods of carbon. The most significant feature of Swan's lamp was that there was little residual oxygen in the vacuum tube to ignite the filament, thus allowing the filament to glow almost white-hot without catching fire. From this year he began installing light bulbs in homes and landmarks in England, and by the early 1880s he had started his own company.

Across the Atlantic, parallel developments were also taking place. On July 24 1874 a Canadian patent was filed for the Woodward and Evans Light by a Toronto medical electrician named Henry Woodward and a colleague Mathew Evans, who was described in the patent as a "gentleman" but was in reality a hotel keeper. They built their lamps with different sizes and shapes of carbon filaments held between electrodes in glass globes filled with nitrogen. Woodward and Evans attempted to commercialize their bulb, but were unsuccessful. Nonetheless, Thomas Edison considered their approach sufficiently promising that he bought the rights to both their Canadian and US patents before embarking on his own light bulb development program.

After many experiments with platinum and other metal filaments, Edison returned to a carbon filament (the first successful test was on October 21 1879; it lasted 13.5 hours). Edison continued to improve this design and by 1880 had the patent for a lamp that could last over 1200 hours using a carbonized bamboo filament. Edison and his team did not find this commercially viable filament until more than 6 months after Edison filed the patent application. Bamboo continued to be used until 1893, later enhanced by a cellulose coating, introduced around 1882 and produced until at least 1929.

In January 1882, Lewis 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.

In Britain, the Edison and Swan companies merged into the Edison and Swan United Electric Company (later known as Ediswan, which was then incorporated into Thorn Lighting Ltd). Edison was initially against this combination, but 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, in order to protect Edison's patents from claims against them in the US.

The United States Patent Office had ruled on 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. Image:Light bulb.png Image:Electric lamp patent.jpg

In addressing the question "Who invented the incandescent lamp?" historians Robert Friedel and Paul Israel (1987, 115-117) 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." (Hughes 1977, 9)

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 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 electronic vacuum tube.) It was a metal-coated carbon filament. In 1906, the General Electric Company was the first to patent a method of making tungsten filaments for use in incandescent light bulbs. The 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.

One of the major problems of the standard electric light bulb is evaporation of the filament. The inevitable variations in resistivity along the filament cause nonuniform heating, with "hot spots" forming at points of higher resistivity. Thinning by evaporation increases resistivity. But hot spots evaporate faster, increasing their resistivity faster—a positive feedback which ends in the familiar tiny gap in an otherwise healthy-looking filament. Irving Langmuir suggested that an inert gas, instead of vacuum, would retard evaporation and still avoid combustion, and so ordinary incandescent light bulbs are now filled with nitrogen, argon, or krypton.

A typical filament light bulb lasts about 1000 hours. See the section below, Voltage, light output, and life, for a discussion of the tradeoffs involved in setting a lamp life specification.

The halogen lamp

Image:Halogen.jpg

One invention that addressed the problem of short lamp life was the halogen lamp, also called the tungsten-halogen lamp, where a tungsten filament is sealed into a clear "capsule" filled with a halogen gas such as iodine or bromine. This type of incandescent lamp creates an equilibrium reaction where the tungsten filament that evaporates when giving off light is chemically re-deposited at the hot-spots, preventing the early failure of the lamp. This also allows halogen lamps to be run at higher temperatures (which would cause unacceptably low lamp lifetimes in ordinary incandescent lamps) allowing for greater brightness, whiter color temperature, and efficiency.

Because the lamp must be very hot to create this reaction, the halogen capsule is often made of fused quartz, instead of ordinary glass which would soften and flow too much at these temperatures. Thus, halogen lamps are sometimes called quartz-halogen lamps, or tungsten-halogen lamps (the filament is tungsten). They were once called quartz iodine lamps. Modern halogen lamps are made of 'doped' quartz with additives to reduce the UV output. Halogen lamps with integrated reflectors often include a transparent UV filter to seal the lamp.

A further development that has added to lamp efficiency is an infrared coating (IRC). The quartz envelope is coated with a multi-layered coating which allows visible light to be emitted while reflecting a portion of the infrared radiation back on to the filament. The result is that less power is needed to produce an equivalent light output. This efficiency increase can be as much as 40% when compared to its standard equivalent.

Perhaps the most significant side effect of using quartz instead of ordinary glass is that the lamp becomes a source of UV-B light, because the quartz is transparent to this spectral range and ordinary glass is not. Quartz halogen lamps are thus used in some scientific instrument as a UV-B light source. One consequence of this is that it is possible to get a sunburn from excess exposure to the light of a quartz halogen lamp. To mitigate the negative effects of UV exposure, some manufacturers add a coating of UV inhibitors on the capsule that effectively filters UV radiation. When this is done correctly, a halogen lamp with UV inhibitors will produce less UV than its standard incandescent counterpart.

Because the halogen lamp is hot, and poses a danger of fire or burns, and because of the risk from UV exposure, these lamps are usually protected by a lens of ordinary glass, which, as noted above, absorbs most of the UV-B light.

The quartz capsule can be damaged by any oils or residue from fingerprints. These lamps should be handled without touching the clear quartz, either by using a clean paper towel or carefully holding the porcelain base. If the quartz is touched, it must be cleaned with rubbing alcohol.

The incandescent lamp is still widely used in domestic applications, and is the basis of most portable lighting, such as table lamps, some car headlamps and electric flashlights. Halogen lamps have become more common in auto headlights and domestic situations, particularly where light is to be concentrated on a particular point. The fluorescent light, has, however, replaced many applications of the incandescent lamp with its superior life and energy efficiency. LED lights are beginning to see increased home and auto use, replacing incandescent lamps. Newer headlights are often high-intensity discharge lamps, such as metal halide lamps, which produce purple-tinted light instead of the usual yellowish color of a standard incandescent bulb.

Heat

Incandescent light bulbs waste about 95% of the power they consume in heat.

An incandescent light bulb (about 5% efficiency) is about one quarter as efficient as a fluorescent lamp (about 20% efficiency), and produces about six times as much heat with the same amounts of light from both sources. One reason why incandescent lamps are unpopular in commercial spaces is that the heat output results in the need for more air conditioning in the summer. Incandescent lamps can usually be replaced by self-ballasted compact fluorescent light bulbs, which fit directly into standard sockets. This lets a 100 W incandescent lamp be replaced by a 23-watt fluorescent bulb, while still producing the same amount of light.

Quality halogen incandescents are closer to 9% efficiency, which, although still extremely low, will allow a 60 W bulb to provide nearly as much light as (and a 75 W to provide even more than) a non-halogen 100 W. However, small halogen lamps are often still high-power, causing them to get extremely hot. This is both because the heat is more concentrated on the smaller bulb surface, and because the surface is closer to the filament. This high temperature is essential to their long life (see the section on halogen lamps above). Left unprotected, these can cause fires much more easily than a regular incandescent, which may only scorch easily flammable objects such as drapery. Most safety codes now require these bulbs to be protected by a grid or grille, or by the glass and metal housing of the fixture. Similarly, in some areas halogen bulbs over a certain power are banned from residential use.

Standard fittings

Image:CompactFluorescentLightBulb.jpg Most domestic and industrial light bulbs have a metal base compatible with standard lamp holders. The most common types of fitting are:

• E12 or candelabra base
• MES or Medium Edison Screw (aka E26), used in the USA and Japan for most 120 and 100 volt lamps
• BC or B22 or double-contact Bayonet Cap, used in Australia, Ireland, New Zealand and the UK for most 240 V mains lamps (MES also common in Australia and the UK)
• E14 / E27 screw fittings, used in continental Europe (E27 is very similar to MES, but not identical)

In each designation, the E stands for Edison, who created the screw-base lamp, and the number is screw cap diameter in eighths of an inch in the U.S. (millimetres in Europe and Asia). In North America, there are four standard sizes of screw-in sockets used for line-voltage lamps:

• E12 candelabra (E10 & E11 in Europe)
• E17 intermediate (E14)
• E26 medium or standard (E27)
• E39 mogul (E40).
• There is also a rare "admedium" size (E29), and a very miniature size (E5), generally used only for low voltage applications such as with a battery. Bayonet bulbs have similar sizes and are given a B designation.

Halogen bulbs often come inside one of these standard fittings, but also come with pin bases. These are given a G or GY designation, with the number being the centre-to-centre 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).

General Electric introduced standard fitting sizes for tungsten incandescent lamps under the 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.

Power

Incandescent light bulbs are usually marketed according to the electrical power consumed. This is measured in watts and depends mainly on the resistance of the filament, which in turn depends mainly on the filament's length, thickness and material. It is difficult for the average consumer to predict the light output of a bulb given the power consumed but it can be safely assumed, for two bulbs of the same type, that the higher-powered bulb is brighter.

Light output ratings are given in lumens, although most buyers do not check for this. Some manufacturers engage in deceptive advertising, such that the claimed "long" bulb life is achievable at normal household voltages, but the claimed light output is only attainable at a higher voltage which does not normally exist, such as 130 volts in the United States.

The table to the right 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.

Also note that the 34, 52, 67, 90 and 135 watt bulbs in the chart are designed for use at 130 volts.

Comparison of electricity cost

A kilowatt-hour is a unit of energy, and this is the unit in which electricity is purchased. (The cost of electricity in the United States ranges from $0.08 to $0.12 per kilowatt-hour (kWh).)

The following shows how to calculate total cost of electricity for using an incandescent light bulb vs. a compact fluorescent light bulb. (Also note that 1 kWh = 1000 Wh).

Electricity Cost (for 800-900 lumens at a rate of $0.10 per kWh)
Image:IncandescentLightBulb.png	<math>\left( 60 \ watts \right) \times \left( 8000 \ hours \right) \times \left( \frac{\ $0.10}{1000 \ watt \cdot hours} \right) = \ $48 </math>
Image:CompactFluorescentLightBulb.png	<math>\ \left( 14 \ watts \right) \times \left( 8000 \ hours \right) \times \left( \frac{\ $0.10}{1000 \ watt \cdot hours} \right) = \ $11.20 </math>

Image:Lightbulb.jpg The average lifetime of incandescent light bulbs is about 750-1000 hours. It would take at least 6-11 incandescent bulbs to last as long as one compact fluorescent, which have an average lifetime between 8,000 and 10,000 hours.

Voltage, light output, and lifetime

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^3.4
• Power consumption is approximately proportional to V^1.6
• Lifetime is approximately inversely proportional to V¹⁶
• Color temperature is approximately proportional to V^0.42

This means that 5% reduction in operating voltage will double the life of the bulb, at the expense of reducing its light output by 20%. This may be a very acceptable tradeoff for a light bulb that is 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 tradeoff.

According to the relationships above (which are probably not accurate for such extreme departures from nominal ratings), operating a 100-watt, 1000-hour, 1700-lumen bulb at half voltage would extend its life to about 65,000,000 hours or over 7000 years – while reducing light output to 160 lumens, about the equivalent of a normal 15 watt bulb. The Guinness Book of World Records states that a fire station in Livermore, California has a light bulb that is said to have been burning continuously for over a century since 1901 (presumably apart from power outages). 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 [1].

In flash lamps used for photographic lighting, the tradeoff 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 °C (90 °F) below that melting point.

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 tradeoff between efficiency and long life. Many modern 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.

Luminous efficacy and efficiency

A light can waste power by emitting too much light outside of the visible spectrum. Only visible light is useful for illumination, and some wavelengths are perceived as brighter than others. Taking this into account, luminous efficacy is a ratio of the useful power emitted to the total radiant flux (power). It is measured in lumens per watt (lm/W). The maximum efficacy possible is 683 lm/W. 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[2]. However, the term luminous efficiency is often used for both quantities.

Another, related, measure is the overall luminous efficiency, which divides by the total power input rather than the total radiant flux. This takes into account more ways that energy might be wasted and so is never greater than luminous efficiency. Image:SEM 60-watt light bulb filament (75x).jpg Image:Incandescent flashlight spectrum.gif

Thus a typical 100 W bulb for 120 V systems, with a rated light output of 1750 lumens, has an efficacy of 17.5 lumens per watt, compared to an "ideal" of 242.5 lumens per watt for one type of white light. Unfortunately, tungsten filaments radiate mostly infrared radiation while still remaining a solid (below 3683 kelvins). Donald L. Klipstein explains it this way: "An ideal thermal radiator produces visible light most efficiently at temperatures around 6300 °C (6600 kelvins 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."<ref name="bulbguide"/> No known material can be used as filament at this ideal temperature; this is hotter than the sun's surface.

See also

• Fluorescent light
• Light bulb
• Lightbulb jokes
• Light-emitting diode (LED)
• List of light fixture manufacturers in the United States
• List of light sources
• Thomas Edison
• Timeline of lighting technology

Notes

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External links, references, resources

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• Energy Efficient Light Bulbs
• Livermore bulb and North Fort Worth Historical Society bulb article
• Livermore Bulb Webcam - light bulb on since 1901
• Edward J. Covington's Early Incandescent Lamps
• Great Internet Light Bulb Book
• Technical Information on Lamps
• Kruger, Anton, "When Can LEDs Replace Incandescent Lamps"?
• Kilokat's Antique Light Bulb Site, photos-history-discussion
• Worth Knowing?! — Technology: Bulb
• The Great Internet Light Bulb Book, Part I, by Donald L. Klipstein
• http://www.mis-bombillas.com/ Little "Virtual Museum of Electric Lamps", from Spain.
• Did Thomas Edison really invent the light bulb?
• Friedel, Robert, and Paul Israel. 1987. Edison's electric light: biography of an invention. New Brunswick, New Jersey: Rutgers University Press.
• 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.
• Hughes, Thomas P. 2004. American Genesis: A Century of Invention and Technological Enthusiasm 1870-1970. 2nd ed. Chicago: The University of Chicago Press.

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