Incandescent light bulb

Incandescent light bulb

The incandescent light bulb, incandescent lamp or incandescent light globe is a source of electric 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 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 lamps.

Incandescent bulbs are made in a wide range of sizes and voltages, 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 headlamps and electric flashlights, 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 tanks, 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 lights, high-intensity discharge lamps, light-emitting diodes (LEDs), and other devices, which give more visible light for the same amount of electrical energy input. Some jurisdictions are attempting to ban the use of incandescent lightbulbs in favour of more energy-efficient lighting.

History of the light bulb

In addressing the question "Who invented the incandescent lamp?" historians Robert Friedel and Paul Israel [ Friedel, Robert, and Paul Israel. 1987. "Edison's electric light: biography of an invention". New Brunswick, New Jersey: Rutgers University Press. pages 115-117 ] list 22 inventors of incandescent lamps prior to Joseph Wilson Swan and Thomas 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, 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". 2nd ed. Chicago: The University of Chicago Press ]

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. 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 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 dividing 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, as well as 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 or 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, such as compact fluorescent lamps or LEDs.

Common shapes:

;General Service:Light emitted in (nearly) 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. [ [ Lighting Glossary] ]

Lamp bases

Most domestic and industrial light bulbs have a metal fitting (or lamp base) compatible with standard sockets. The lamp base must carry current to the lamp, provide physical support, and resist heat. Lamp bases may be secured to the bulb with a cement, or by mechanical crimping to indentations molded into the glass bulb. Some miniature lamps have no metal bases at all and have only wire leads molded into the bulb. General Electric introduced standard base 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.

crew thread

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.

The largest size E39 is used on large street lights, 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 V are also produced for recreational vehicles. Large outdoor Christmas lights use an intermediate base, as do some desk lamps and many microwave ovens. 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. [ General Electric TP 110 page 12 ]

Screw bases suffer from the disadvantage that as they only have a single central contact, the metal screw itself forms one of the contacts for the circuit. If the lighting system is not correctly designed or wired, the metal screw can become live presenting a hazard to anyone attempting to change the bulb.


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 common in 12-volt automobile lighting worldwide.

BC or B22 or B22d or double-contact bayonet cap light bulbs are used for most 220–240 V mains lamps in the UK, Ireland, Cyprus, Australia, India, New Zealand, and various other parts of the British Commonwealth (but not Canada). 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 machines and vacuum cleaners.

These are the available sizes in the UK: [see] Of these, only the BC (Ba22d) is commonly sold in supermarkets.

Pin base

A pin base has two contact pins on the underside of the bulb. 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 spotlights or 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.

pecial lamp bases

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

There are also special bases for projectors and stage lighting instruments. Projector lamps [ The Basics About Projector Lamps] . Published by PartStore, accessed on June 29, 2007.] , 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 systemFact|date=August 2008.

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. [cite web| Stockholms universitet|url="MT0414 Lampa, halogen, 300W, R7s-15 Haloline" / see picture]

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 proportional to "V" −16
*"Color temperature" is approximately proportional to "V" 0.42 [ 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 ] 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 tradeoff. 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. [ General Electric TP-110, page 20 ]

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. [ [ Magazine Online ] ]

In flood 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, 3695 K (6192° F). A 50-hour-life projection bulb, for instance, is designed to operate only 50 °C (90 °F) below that melting point. Such a lamp may achieve up to 22 lumens/watt, compared with 17.5 for a 750-hour general service lamp. [ General Electric TP-110, page 19 ]

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. [ General Elecric TP 110 pg. 19 ] This comes about because the lower voltage lamps have a correspondingly thicker filament which has a smaller surface area than its thinner higher-voltage counterpart. The smaller surface area reduces the rate at which the filament evaporates which allows the filament to be run hotter for the same life.Fact|date=September 2008

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 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 for incandescent lamps is 1.5 volts. Very long filaments for high voltages are fragile, and lamp bases become more difficult to insulate, so lamps for illumination are not made with rated voltages over 300 V. [ General Electric TP 110 ] Some infrared heating elements are made for higher voltages, but these use tubular bulbs with widely-separated terminals.

Luminous efficacy and efficiency

Approximately 90% of the power consumed by an incandescent light bulb is emitted as heat, rather than as visible light. [ General Electric TP-110, page 23, table. ]

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 lumens per watt (lm/W). The maximum efficacy possible is 683 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. [] 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 compares a broader array of light sources to one another.

A 100-watt, 120-volt bulb 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 kelvins). Donald L. Klipstein explains it this way: "An ideal thermal radiator produces visible light most efficiently at temperatures around 6300 °C (6600 K or 11 500 °F). Even at this high temperature, a lot of the radiation is either infrared or ultraviolet, and the theoretical luminous efficiency is 95 lumens per watt." 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. [ General Electric TP-110 page 19 ]

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. [Prof. Peter Lund, Helsinki University of Technology, [] on p. C5 in Helsingin Sanomat Oct. 23, 2007.]

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

Alternatives to standard incandescent lamps for general lighting purposes include:
*Fluorescent lamps, and Compact fluorescent lamps
*High-intensity discharge lamps
*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 lines 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 temperatures of white for visible light.

Laws and regulations to discontinue use

Due to the higher energy usage of incandescent light bulbs in comparison to more energy efficient alternatives, such as compact fluorescent lamps and LED lamps, 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, Italy in 2011, 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 (with minor exceptions).

Efforts to improve efficiency

Various efforts to improve the efficiency of incandescent lamps have been made recently, due to legislation and other movements to 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. [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] [ [ GE Announces Advancement in Incandescent Technology; New High-Efficiency Lamps Targeted for Market by 2010] ]

In 2006, David Cunningham, who has produced many innovations in entertainment lighting, filed for a US Patent for a lamp using an infrared reflector. [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]

The US Department of Energy is also currently developing a filament lamp at Sandia National Laboratories with improved efficiency from 5% to 60%. [Citation | title = Proposed Bulb Ban Causes Chain Reaction | newspaper = Projection Lights and Staging News (PLSN) Online | year = 2008 | date = January 2008 | url =] [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]

ee also

* Centennial Light
* Flash (photography) and discussion of flashbulbs
* Fluorescent lamp
* Lightbulb jokes
* 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


External links

* [ Howstuffworks - "How Light Bulbs Work"]
* [ Light Source Spectra] 60W-100W Incandescent light bulb spectra
* [ Light Bulb Base Identification]
* [ Light Bulbs - Lamps and Tubes - Lamp Bases Explained]
* [ The Perfection of the Electric Light Bulb] - background and experiment
* [ Light Bulb Color Temperature Selector]
* [ Incandescent Light Bulb's Bulb and Base Types Explained]

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