Incandescent light bulb

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A 230-volt incandescent light bulb, with a 'medium' sized E27 (Edison 27 mm) male screw base. The filament is visible as the horizontal line between the vertical supply wires.



Incandescent bulbs are much less efficient than most other types of electric lighting; incandescent bulbs convert less than 5% of the energy they use into visible light[1] (with the remaining energy being converted into heat). The luminous efficacy of a typical incandescent bulb is 16 lumens per watt, compared to the 60 lm/W of a compact fluorescent bulb. Some applications of the incandescent bulb deliberately use the heat generated by the filament. Such applications include incubators, brooding boxes for poultry,[2] heat lights for reptile tanks,[3] infrared heating for industrial heating and drying processes, lava lamps, and the Easy-Bake Oven toy. Incandescent bulbs typically have short lifetimes compared with other types of lighting; around 1,000 hours for home light bulbs versus typically 10,000 hours for compact fluorescents and 30,000 hours for lighting LEDs.

Incandescent bulbs are gradually being replaced in many applications by other types of electric light, such as fluorescent lamps, compact fluorescent lamps (CFL), cold cathode fluorescent lamps (CCFL), high-intensity discharge lamps, and light-emitting diode lamps (LED). Some jurisdictions, such as the European Union, China, Canada and United States, are in the process of phasing out the use of incandescent light bulbs while others, including Colombia,[4] Mexico, Cuba, Argentina, Brazil or Australia,[5] have prohibited them already.





—Thomas P. Hughes, In Technology at the Turning Point, edited by W. B. Pickett[7][8]

Early pre-commercial research

Original carbon-filament bulb from Thomas Edison's shop in Menlo Park

In 1802, Humphry Davy had what was then the most powerful electrical battery in the world at the Royal Institution of Great Britain (with the possible exception of another one made in the same year by Vasily Petrov in Russia[citation needed]). In that year, Davy 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.[10]

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. Many of these devices were demonstrated and some were patented.[11]

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". 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 et al.[12] with being the inventor of the "Incandescent Light Bulb".



In 1845, American John W. Starr[14] acquired a patent for his incandescent light bulb involving the use of carbon filaments.[15] He died shortly after obtaining the patent, and his invention was never produced commercially. Little else is known about him.[16]


In 1872, Russian Alexander Lodygin invented an incandescent light bulb and obtained a Russian patent in 1874. He used as a burner two carbon rods of diminished section in a glass receiver, hermetically sealed, and filled with nitrogen, electrically arranged so that the current could be passed to the second carbon when the first had been consumed.[18] Later he lived in the USA, changed his name to Alexander de Lodyguine and applied and obtained patents for incandescent lamps having chromium, iridium, rhodium, ruthenium, osmium, molybdenum and tungsten filaments,[19] and a bulb using a molybdenum filament was demonstrated at the world fair of 1900 in Paris.[20]



Carbon filament lamps, showing darkening of bulb


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 in 1880.[24][dubious ] 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 upon Tyne on 3 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.[25] 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.[24] 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 hydroelectric power. In 1878 the home of Lord Armstrong at Cragside was also among the first houses to be lit by electricity. In the early 1880s he had started his company.[26] In 1881, the Savoy Theatre in the City of Westminster, 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.[27]

Edison carbon filament lamps, early 1880s

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 14 October 1878.[28] After many experiments, first with carbon in the early 1880s and then with platinum and other metals, in the end Edison returned to a carbon filament.[29] The first successful test was on 22 October 1879,[30][31] and lasted 13.5 hours. Edison continued to improve this design and by 4 November 1879, filed for a US patent for an electric lamp using "a carbon filament or strip coiled and connected ... to platina contact wires."[32] Although the patent described several ways of creating the carbon filament including using "cotton and linen thread, wood splints, papers coiled in various ways,"[32] Edison and his team later discovered that a carbonized bamboo filament could last more than 1200 hours.[33] In 1880, the Oregon Railroad and Navigation Company steamer, Columbia, became the first application for Edison's incandescent electric lamps (it was also the first ship to execute use of a dynamo).[34][35][36] Columbia sank in a collision with a schooner off California in 1907.

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, 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 Columbia. In October 1880, Maxim patented a method of coating carbon filaments with hydrocarbons to extend their life.




In 1882, the first recorded set of miniature incandescent lamps for lighting a Christmas tree was installed.[citation needed] These did not become common in homes for many years.


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.[citation needed]

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.[citation needed]

In 1901, American businessman Frank A. Poor purchased the Merritt Manufacturing Company, the predecessor to North American light bulb makers Hygrade and Osram Sylvania. Poor's firm in Middleton, Massachusetts, specialized in refilling burned-out light bulbs until 1916.[citation needed]

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

Tungsten bulbs

Hungarian advertising of the Tungsram-bulb from 1904. This was the first light bulb that used a filament made from tungsten instead of carbon. The inscription reads: wire lamp with a drawn wire – indestructible.

On 13 December 1904, Hungarian Sándor Just and Croatian Franjo Hanaman were granted a Hungarian patent (No. 34541) for a tungsten filament lamp that lasted longer and gave brighter light than the carbon filament. Tungsten filament lamps were first marketed by the Hungarian company Tungsram in 1904. This type is often called Tungsram-bulbs in many European countries.[40] Their experiments also showed that the luminosity of bulbs filled with an inert gas was higher than in vacuum.[41] The tungsten filament outlasted all other types.

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.

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.





Efficacy, efficiency, and environmental impact

Xenon halogen lamp (105 W) with an E27 base, intended for direct replacement of a non-halogen bulb

Of the power consumed by typical incandescent light bulbs, 95% or more is converted into heat rather than visible light.[1] Other electrical light sources are more effective.

Luminous efficacy of a light source may be defined in two ways. The radiant luminous efficacy (LER) is the ratio of the visible light flux emitted (the luminous flux) to the total power radiated over all wavelengths. The source luminous efficacy (LES) is the ratio of the visible light flux emitted (the luminous flux) to the total power input to the source, such as a lamp.[45] Visible light is measured in lumens, a unit which is defined in part by the differing sensitivity of the human eye to different wavelengths of light. Not all wavelengths of visible electromagnetic energy are equally effective at stimulating the human eye; the luminous efficacy of radiant energy (LER) is a measure of how well the distribution of energy matches the perception of the eye. The units of luminous efficacy are "lumens per watt" (lpw). The maximum LER possible is 683 lm/W for monochromatic green light at 555 nanometers wavelength, the peak sensitivity of the human eye.

The luminous efficiency is defined as the ratio of the luminous efficacy to the theoretical maximum luminous efficacy of 683 lpw, and, as for luminous efficacy, is of two types, radiant luminous efficiency (LFR) and source luminous efficacy (LFS).

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. The values for the incandescent bulbs are source efficiencies and efficacies. The values for the ideal sources are radiant efficiencies and efficacies. A similar chart in the article on luminous efficacy compares a broader array of light sources to one another.

Type Overall luminous efficiency Overall luminous efficacy (lm/W)
40 W tungsten incandescent 1.9% 12.6[1]
60 W tungsten incandescent 2.1% 14.5[1]
100 W tungsten incandescent 2.6% 17.5[1]
glass halogen 2.3% 16
quartz halogen 3.5% 24
photographic and projection lamps with very high filament temperatures and short lifetimes 5.1% 35[46]
ideal black-body radiator at 4000 K (or a class K star like Arcturus) 7.0% 47.5
ideal black-body radiator at 7000 K (or a class F star like Procyon) 14% 95
ideal monochromatic 555 nm (green) source 100% 683[47]

The spectrum emitted by a blackbody radiator at temperatures of incandescent bulbs does not match the sensitivity characteristics of the human eye; the light emitted does not appear white, and most is not in the range of wavelengths at which the eye is most sensitive. Tungsten filaments radiate mostly infrared radiation at temperatures where they remain solid – below 3,695 K (3,422 °C; 6,191 °F). Donald L. Klipstein explains it this way: "An ideal thermal radiator produces visible light most efficiently at temperatures around 6,300 °C (6,600 K; 11,400 °F). Even at this high temperature, a lot of the radiation is either infrared or ultraviolet, and the theoretical luminous efficacy (LER) is 95 lumens per watt."[46] 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 (LER) is around 52 lumens per watt, the theoretical value emitted by tungsten at its melting point.[43]

Although inefficient, incandescent light bulbs have an advantage in applications where accurate color reproduction is important, since the continuous blackbody spectrum emitted from an incandescent light-bulb filament yields near-perfect color rendition, with a color rendering index of 100 (the best possible).[48] White-balancing is still required to avoid too "warm" or "cool" colors, but this is a simple process that requires only the color temperature in Kelvin as input for modern, digital visual reproduction equipment such as video or still cameras unless it is completely automatized. The color-rendering performance of incandescent lights cannot be matched by LEDs or fluorescent lights, although they can offer satisfactory performance for non-critical applications such as home lighting.[49][50] White-balancing such lights is therefore more complicated, requiring additional adjustments to reduce for example green-magenta color casts, and even when properly white-balanced, the color reproduction will not be perfect.

Thermal image of an incandescent bulb. Much of the energy is emitted as infrared. The IR heats the glass, which conducts the heat to the surrounding air, producing convection.

For a given quantity of light, an incandescent light bulb produces more heat (and thus consumes more power) than a fluorescent lamp. In buildings where air conditioning is used, incandescent lamps' heat output increases load on the air conditioning system.[51] Heat from lights will displace heat required from a building's heating system, but generally space heating energy is of lower cost than heat from lighting.

Halogen incandescent lamps have higher efficacy, which will allow a halogen light to use less power to produce the same amount of light compared to a non-halogen incandescent light. The expected life span of halogen lights is also generally longer compared to non-halogen incandescent lights, and halogen lights produce a more constant light-output over time, without much dimming.[52]

There are many non-incandescent light sources, such as the fluorescent lamp, high-intensity discharge lamps and LED lamps, which have higher luminous efficiency, and some have been designed to be retrofitted in fixtures for incandescent lights. These devices produce light by luminescence. These lamps produce discrete spectral lines and do not have the broad "tail" of invisible infrared emissions. By careful selection of which electron energy level transitions are used, and fluorescent coatings which modify the spectral distribution, the spectrum emitted can be tuned to mimic the appearance of incandescent sources, or other different color temperatures of white light. Due to the discrete spectral lines rather than a continuous spectrum, the light is not ideal for applications such as photography and cinematography.[49][50]

Cost of lighting


Measures to ban use

Since incandescent light bulbs use more energy than alternatives such as CFLs and LED lamps, many governments have introduced measures to ban their use,[54] by setting minimum efficacy standards higher than can be achieved by incandescent lamps.

In the US, federal law has scheduled the most common incandescent light bulbs to be phased out by 2014, to be replaced with more energy-efficient light bulbs.[55] Traditional incandescent light bulbs were phased out in Australia in November 2009.[56]

Objections to banning the use of incandescent light bulbs include the higher initial cost and quality of light of alternatives.[57] Some people have concerns about the health effects of fluorescent lamps.

Efforts to improve efficiency

Some research has been carried out to improve the efficacy of commercial incandescent lamps. In 2007, the consumer lighting division of General Electric announced a "high efficiency incandescent" (HEI) lamp project, 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 twice as efficient.[58][59] The HEI program was terminated in 2008 due to slow progress.[60][61]

US Department of Energy research at Sandia National Laboratories initially indicated the potential for dramatically improved efficiency from a photonic lattice filament.[58] However, later work indicated that initially promising results were in error.[62]

Prompted by US 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.[63]



The bulb is filled with an inert gas such as argon (93%) and nitrogen (7%) to reduce evaporation of the filament and prevent its oxidation at a pressure of about 70 kPa (0.7 atm).[64] Early lamps, and some small modern lamps used only a vacuum to protect the filament from oxygen.

An electric current heats the filament to typically 2,000 to 3,300 K (3,140 to 5,480 °F), well below tungsten's melting point of 3,695 K (6,191 °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. The useful part of the emitted energy is visible light, but most energy is given off as heat 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. 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.

Most light bulbs have either clear or coated glass. The coated glass bulbs have a white powdery substance on the inside called kaolin. Kaolin, or kaolinite, is a white, chalky clay in a very fine powder form, that is blown in and electrostatically deposited on the interior of the bulb. It diffuses the light emitted from the filament, producing a more gentle and evenly distributed light. Manufacturers may add pigments to the kaolin to adjust the characteristics of the final light emitted from the bulb. Kaolin diffused bulbs are used extensively in interior lighting because of their comparatively gentle light. Other kinds of colored bulbs are also made, including the various colors used for "party bulbs", Christmas tree lights and other decorative lighting. These are created by staining the glass with a dopant; which is often a metal like cobalt (blue) or chromium (green).[65] Neodymium-containing glass is sometimes used to provide a more natural-appearing light.

Incandescent light bulb.svg
  1. Outline of Glass bulb
  3. Tungsten filament
  4. Contact wire (goes out of stem)
  5. Contact wire (goes into stem)
  7. Stem (glass mount)
  8. Contact wire (goes out of stem)
  9. Cap (sleeve)
  10. Insulation (vitrite)
  11. Electrical contact

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 for incandescent light bulbs range from about 0.1 watt to about 10,000 watts.


Further information: Lightbulb socket


Tantalum filament light bulb, 1908, the first metal filament bulb

Early lamps were laboriously assembled by hand. After automatic machinery was developed the cost of lamps fell.

In manufacturing the glass bulb, a type of "ribbon machine" is used. 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 the ribbon machine; a typical machine of this sort produces 50,000 bulbs per hour.[66] The filament and its supports are assembled on a glass stem, which is fused to the bulb. The air is pumped out of the bulb, and the evacuation tube in the stem press is sealed by a flame. The bulb is then inserted into the lamp base, and the whole assembly tested.


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. 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. 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, 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.

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. The metal filament had the property of gradually shortening in use; the filaments were installed with large loops that tightened in use. This made lamps in use for several hundred hours quite fragile.[67] Metal filaments had the property of breaking and re-welding, though this would usually decrease resistance and shorten the life of the filament. General Electric bought the rights to use tantalum filaments and produced them in the US until 1913.[68]

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

How a tungsten filament is made

In 1906, the tungsten filament was introduced. Tungsten metal was initially not available in a form that allowed it to be drawn into fine wires. 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 tungsten powder into bars, then several steps of sintering, swaging, and then wire drawing. It was found that very pure tungsten formed filaments that sagged in use, and that a very small "doping" treatment with potassium, silicon, and aluminium oxides at the level of a few hundred parts per million greatly improved the life and durability of the tungsten filaments.[70]

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 (580 mm),[43] and the filament diameter is 0.0018 inches (0.046 mm). 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. 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.

Filament of a 200-watt incandescent lightbulb highly magnified


Reducing filament evaporation

One of the problems of the standard electric light bulb is evaporation of the filament. Small variations in resistivity along the filament cause "hot spots" to form at points of higher resistivity;[44] a variation of diameter of only 1% will cause a 25% reduction in service life.[43] The hot spots evaporate faster than the rest of the filament, increasing resistance at that point—a positive feedback that 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,[71] or sometimes krypton.[72] 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.[73] More nitrogen is used in higher-voltage lamps to reduce the possibility of arcing.



Filament notching describes another phenomenon that limits the life of lamps. Lamps operated on direct current develop random stairstep 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.[75][76]


Bulb blackening


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. Hydrogen from water vapor reduces the oxide, reforming water vapor and continuing this water cycle.[44] The equivalent of a drop of water distributed over 500,000 lamps will significantly increase darkening.[43] 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.


Halogen lamps

Main article: Halogen lamp


Incandescent arc lamps


Electrical characteristics

Comparison of efficacy by power
120 volt lamps[82] 230 volt lamps[83]
5 25 5
15 110 7.3
25 200 8.0 206 8.24
40 500 12.5 330 8.25
60 850 14.2 584 9.73
75 1,200 16.0
100 1,700 17.0 1,160 11.6
150 2,850 19.0
200 3,900 19.5 2,725 13.62
300 6,200 20.7 4,430 14.77
500 7,930 15.86


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. 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. 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. Light output of a 230 V version is usually slightly less than that of a 120 V version. The lower current (higher voltage) filament is thinner and has to be operated at a slightly lower temperature for same life expectancy, and that reduces energy efficiency.[84] The lumen values for "soft white" bulbs will generally be slightly lower than for clear bulbs at the same power.

Current and resistance


Carbon filament bulbs have the opposite characteristic. The resistance of a carbon filament is higher when it is cold than when it is operating. In the case of a 240 Volt, 60 Watt carbon filament bulb, the resistance of the filament when at operating temperature is 960 Ohms, but rises to around 1500 Ohms when cold.

Physical characteristics

Bulb shapes

Incandescent light bulbs come in a range of shapes and sizes.

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. The letters represent the shape of the bulb. The numbers represent the maximum diameter, either in 18 of an inch, or in millimeters, depending on the shape and the region. For example, 63 mm reflectors are designated R63, but in the US, they are known as R20 (2.5 in).[87] However, in both regions, a PAR38 reflector is known as PAR38.

Common shapes:

General Service
120 V sizes: A17, 19 and 21
230 V sizes: A55 and 60
High Wattage General Service
Lamps greater than 200 watts.
Types: Pear-shaped (PS)
lamps used in chandeliers, etc.
230 V sizes: P45, G95
Reflector (R)
Types: Standard reflector (R), elliptical reflector (ER), crown-silvered
120 V sizes: R16, 20, 25 and 30
230 V sizes: R50, 63, 80 and 95
Parabolic aluminized reflector (PAR)
Available in numerous spot and flood beam spreads. Like all light bulbs, the number represents the diameter of the bulb in 18 of an inch. Therefore, a PAR 16 is 2 in in diameter, a PAR 20 is 2.5 in in diameter, PAR 30 is 3.75 in and a PAR 38 is 4.75 in in diameter.
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.[88] The Osram designation for a similar coating is "IRC".[89]

Lamp bases

Main article: Lightbulb sockets
The double-contact bayonet cap on an incandescent bulb

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. 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. This standard was soon adopted across the US, 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 bayonet base. Technical standards for lamp bases include ANSI standard C81.67 and IEC standard 60061-1 for common commercial lamp sizes, to ensure interchangeablitity between different manufacturer's products. 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.[90]


Miniature lamps used for some automotive lamps or decorative lamps have wedge bases that 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.

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.

Light output and lifetime

The Centennial Light is the longest-lasting light bulb in the world.
See also: Lamp rerating



  • 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[91]







See also


  1. ^ a b c d e Keefe, T.J. (2007). "The Nature of Light". Archived from the original on 2012-07-24. Retrieved 2007-11-05. 
  2. ^ "Storey's guide to raising chickens" Damerow, Gail. Storey Publishing, LLC; 2nd edition (12 January 1995), ISBN 978-1-58017-325-4. page 221. Retrieved 10 November 2009.
  3. ^ "277 Secrets Your Snake and Lizard Wants you to Know Unusual and useful Information for Snake Owners & Snake Lovers" Cooper,Paulette. Ten Speed Press (1 March 2004), ISBN 978-1-58008-035-4. Page 161. Retrieved 10 November 2009.
  4. ^ "El peligro de los bombillos ahorradores". El Espectador. Retrieved 22 October 2014. 
  5. ^ "Informe técnico preliminar - Estándar mínimo de eficiencia energética". Ministry of Energy - Chile. Retrieved 22 October 2014. 
  6. ^ Friedel, Robert, and Paul Israel. 1986. Edison's electric light: biography of an invention. New Brunswick, New Jersey: Rutgers University Press. pages 115–117
  11. ^ Houston and Kennely 1896, chapter 2
  12. ^ Challoner, Jack etal "1001 Inventions That Changed The World" Barrons Educational Series, Hauppauge NY, 2009.
  13. ^ Houston and Kennely 1896, page 24
  16. ^ "John Wellington Starr". Retrieved 2010 February 16.
  17. ^ Many of the above lamps are illustrated and described in Edwin J. Houston and A. E. Kennely "Electric Incandescent Lighting", The W. J. Johnston Company, New York, 1896 pages 18–42. Available from the Internet Archive.
  20. ^ Principales découvertes et publications concernant l'électricité de 1562 a 1900
  22. ^ "Patent no. 3738. Filing year 1874: Electric Light". Library and Archives Canada. Retrieved 17 June 2013. 
  23. ^ Henry Woodward and Mathew Evans Lamp retrieved 2010 February 16
  24. ^ a b Swan K R Sir Joseph Swan and the Invention of the Incandescent Electric Lamp. 1946 Longmans, Green and Co. Pp 21–25.
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  28. ^ U.S. Patent 0,214,636.
  30. ^ Paul Israel, Edison: a Life of Invention, Wiley (1998), page 186.
  32. ^ a b U.S. Patent 0,223,898 granted 27 January 1880
  37. ^ U.S. Patent 252,386PROCESS OF MANUFACTURING CARBONS. by LEWIS H. LATIMER. Application on February 19, 1881
  40. ^ "The History of Tungsram" (PDF). Archived from the original on 30 May 2005. 
  41. ^ Information About Old Light Bulbs |
  45. ^ IEEE Std. 100 definition of "luminous efficacy" pg. 647
  46. ^ a b Klipstein, Donald L. (1996). "The Great Internet Light Bulb Book, Part I". Retrieved 16 April 2006. 
  47. ^ See luminosity function.
  48. ^ History of the incandescent light
  49. ^ a b LED lights - How it works - History
  50. ^ a b The fluorescent light - How it works & History
  52. ^ Halogen lights - How they work & History
  53. ^ Incandescent Bulbs Still Suck: Why the Bulb as Heater Argument Falls Short
  54. ^ "Is Environmentalism Really Working?: Germany's Eco-Trap". Der Spiegel. 17 March 2010. Retrieved 20 March 2011. 
  55. ^ "It's lights out for traditional light bulbs". USA Today. 16 December 2007.
  56. ^ Department of Climate Change and Energy Efficiency (2 February 2011). "Lighting – Think Change". Retrieved 15 May 2011. 
  57. ^ "Incandescent Bulbs Return to the Cutting Edge". The New York Times. 6 July 2009. 
  58. ^ a b Daley, Dan (February 2008). "Incandescent's Not-So-Dim Future". Projection, Lights & Staging News 09 (1) (Timeless Communications Corp). p. 46. Retrieved 17 June 2013. 
  59. ^ "GE Announces Advancement in Incandescent Technology; New High-Efficiency Lamps Targeted for Market by 2010". Business Wire. 23 February 2007. Retrieved 18 June 2013. 
  60. ^ Hamilton, Tyler (22 April 2009). "Why the brightest idea needs tinkering". Toronto Star. Retrieved 18 June 2013. 
  61. ^ Rahim, Saqib (28 June 2010). "The Incandescent Bulb Heads Offstage After Century-Long Performance". The New York Times. Retrieved 18 June 2013. 
  62. ^ "Revolutionary tungsten photonic crystal could provide more power for electrical devices". Sandia National Laboratories. 7 July 2003. Retrieved 18 June 2013. 
  63. ^ Broydo Vestel, Leora (6 July 2009). "Incandescent Bulbs Return to the Cutting Edge". The New York Times. Retrieved 6 July 2009. 
  64. ^ – Argon (Ar) Properties, Uses, Applications Argon Gas and Liquid Argon, 2007
  65. ^ "Lamp Material Information Sheet – Incandescent Lamp". Retrieved 20 May 2013. 
  66. ^ Light Bulb: How Products are Made
  68. ^ "GE Tantalum Filament 25W of American Design". Museum of Electric Lamp Technology. Retrieved 17 June 2013. 
  69. ^ "The Osmium Filament Lamp"
  70. ^ Chapter 2 The Potassium Secret Behind Tungsten Wire Production
  72. ^ Burgin. Lighting Research and Technology 1984 16.2 61–72
  73. ^ Hunt, Robert (2001–2006). "Glass Blowing for Vacuum Devices – Lamp Autopsy". Teralab. Retrieved 2 May 2007. 
  74. ^ Lipstein, Don. "Premium Fill Gasses". Retrieved 13 October 2011. 
  75. ^ Toshiba Lighting Products Miniature Lamp Characteristics. Retrieved 23 March 2008.
  77. ^ IEC 60064 Tungsten filament lamps for domestic and similar general lighting purposes.
  79. ^ "Incandescent Arc Lamps". Museum of Electric Lamp Technology. 2004. Retrieved 17 June 2013. 
  81. ^ S. G. Starling, An Introduction to Technical Electricity', McMillan and Co., Ltd., London 1920, pp. 97–98, available at the Internet Archive, good schematic diagram of the Pointolite lamp
  83. ^ Roy, Kamesh (2006), Illuminating Engineering, p. 30, ISBN 8170088984, retrieved 7 November 2012 
  84. ^
  86. ^ page 23, 24
  87. ^ "Identification Guide". KO Lighting. Retrieved 18 June 2013. 
  88. ^ Lighting Glossary
  89. ^ Osram IRC Saver calculator
  90. ^ "Single-Ended Halogen Bases". Retrieved 17 June 2013. 
  92. ^ Krajewski, Markus (24 Sep 2014). "The Great Lightbulb Conspiracy". IEEE Spectrum. IEEE. Retrieved 10 Nov 2014. 

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