light bulb

An incandescent lamp bulb and its glowing filament.

The incandescent light bulb (also spelled lightbulb) or incandescent lamp is a source of artificial light that works by incandescence. An electrical 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 called electric lamps, a term originally applied to the original arc lamps, and in Australia they are commonly called light globes.

Incandescent bulbs are made in a wide range of sizes and voltages, from just a few volts up to several hundred volts. They requires no external regulating equipment and have a low manufacturing cost. As a result the incandescent lamp is widely used in household and commerical 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, and the Easy-Bake Oven toy. Residents of highly insulated homes, especially in Scandinavia, use the heat emitted by incandescent bulbs to heat the home.

Very small bulbs are often used for Christmas lighting

Incandescent light bulbs are gradually being replaced in many applications by (compact) fluorescent lights, high-intensity discharge lamps, LEDs, and other devices, which give more visble light for the same amount of electrical energy input. Brazil and Venezuela were the first countries to attempt to phase out the use of incandescent light bulbs in 2005. Australia has announced it will phase out incandescent light bulbs in favour of compact fluorescent lights by 2010.^[1] Politicians in other countries have proposed similar measures (see the Proposals to outlaw section).

History of the light bulb

In addressing the question "Who invented the incandescent lamp?" historians Robert Friedel and Paul Israel ^[2] 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." ^{[3] [4]}

Early pre-commercial reesearch

In 1802 Humphry Davy had what was then the most powerful 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 practical incandescent lamp in 1879.^[6] 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. Demonstrated to the Royal Institution in 1810, the invention came to be known as the Arc lamp.

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.

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.^{[7] [8]}

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 Wellington Starr acquired a patent for his own incandescent light bulb involving the use of carbon filaments.^[9] 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 invented an incandescent light bulb. In 1874 he got a patent for his invention.

In a suit filed by rivals seeking to get around Edison's lightbulb patent, the German-American inventor Heinrich Göbel claimed he had 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 that the bulbs Göbel had purportedly built in the 1850s had actually been built much later, and actually found the glassblower who had constructed the fraudulent exhibits for Göbel.^[10] In a patent interference suit in 1893, the judge ruled that Göbel's claim was "extremely improbable."

Carbon filament lamp (E27 socket, 220 volts, approx. 30 watts, left side: running with 100 volts

Commercialization

Joseph Wilson Swan (1828–1914) was a physicist and druggist (chemist) born in Sunderland, United Kingdom. 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.^[11] On 18th December 1878 a lamp using a slender carbon rod was shown at a meeting of the Newcastle Chemical Society, and he 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. 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.^[12] From this year he began installing light bulbs in homes and landmarks in England, and in the early 1880s he had started his own company. See also ^[13]

In North America, 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. 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.

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 (U.S. Patent  ). After many experiments with platinum and other metal filaments, Edison returned to a carbon filament. The first successful test was on October 22 1879;^[14] and lasted 13.5 hours. Edison continued to improve this design and by Nov 4, 1879, filed for a U.S. patent (granted as U.S. Patent   on Jan 27, 1880) for an electric lamp using "a carbon filament or strip coiled and connected ... to platina contact wires."^[15] Although the patent described several ways of creating the carbon filament including using "cotton and linen thread, wood splints, papers coiled in various ways,"^[15] 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.^[10]

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 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, in order to protect Edison's patents from claims against them in the US.

U.S. Patent   by Thomas Edison for an improved electric lamp, January 27 1880

The United States Patent Office gave a ruling October 8, 1883 that Edison's patents were based on the prior art of William Sawyer and were invalid. Litigation continued for a number of years. 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 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. In the same year Franjo Hannaman, a Croatian from Zagreb, invented a tungsten (wolfram) filament lamp, which lasted longer and gave a brighter light than the carbon filament. 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. 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.

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 and reduce the required strength of the glass. Inside of the bulb is a filament of tungsten wire, through which an electrical 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 with a continuous spectrum. The useful part of the emitted energy is visible light, but also significant energy is given off in the in the near-infrared wavelengths.

Glass bulb Low pressure inert gas 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 (Vitrit) Electrical contact

Incandescent light bulbs usually contain a glass mount on the inside, which supports the filament 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 only used 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 electrical 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 length of the filament is usually 6.5 feet or 2 meters.

An SEM image (75x) of a 60 W line voltage light bulb filament. In order to increase the filament length while keeping its physical size small, the filament takes the form of a coiled coil. By comparison, low voltage lamp filaments usually take the form of a single coil.

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. The hot spots evaporate faster than the rest of the filament, increasing restitance at that point—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 so ordinary incandescent light bulbs are now filled with nitrogen, argon, or krypton. 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 flow; intentionally thin lead-in wires or more elaborate protection devices are therefore often used as fuses built into the light bulb.^[16]

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 hours for lamps used for general illumination. Theatrical, photographic, and motion-picture lamps may have a useful life of only a few hours, trading life expectancy for high output in a compact form.

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.

In a halogen lamp uneven evaporation of the filament and darkening of the envelope is reduced by filling the lamp with a halogen gas. 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.

When a light bulb envelope breaks while the lamp is on or if air leaks into the envelope, 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.^[17]

Electrical Characteristics

Incandescent lamps are nearly pure resistive loads which means they have a power factor of 1. This means the actual power consumed (in watts) and the apparent power (in volt-amperes) are equal. The actual resistance of the filament is temperature dependent. The cold resistance is about one-fifth 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. Since incandescent lamps are resistive loads,simple triac dimmers can be used to control brightness. So-called "iron" ballasts for fluorescent and HID lamps consume reactive power which may be a design concern in large lighting installations.

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. For two bulbs of the same type, colour, and clarity, that the higher-powered bulb is brighter.

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

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 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, where Compact Fluorescent light bulbs are particularly popular.)

The following shows how to calculate total cost of electricity for using an incandescent light bulb vs. a compact fluorescent light bulb ^[18]. (Also note that 1 kWh = 1000 Wh).

Electricity Cost (for 800–900 lumens at a rate of $0.10/kWh)

The average rated laboratory lifetime of incandescent light bulbs is about 750–1000 hours (usually defined as the time it takes half of a given set of lamps to fail under test conditions). Based on rated lifetime, it would take at least 6-11 incandescent bulbs to last as long as one compact fluorescent, which have an average lifetime between 11,250 and 15,000 hours.^[19] This causes an additional total cost of using incandescent bulbs. Another additional (potential) cost may be incurred if the bulbs are not in a readily accessible location and special equipment (e.g., cherry picker) and/or personnel are needed to replace it. Also note that the above calculations are not a reliable measure of the "cost" of a lightbulb; one should multiply the wattage (in kilowatts) by the cost of electricity (money per kilowatt hour) by the number of hours the lightbulb is used every month or year.

Physical characteristics

Bulb shapes, sizes, and terms

• General Service (A)

Light emitted in all directions. Available in either clear or frosted. Types: General (A), Globe (G), Decorative (D) (flame, teardrop and other shapes)

• 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.

• 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 (PAR) 16, 20, 30 and 38 bulbs: 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, 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. ^[20]

Standard fittings

A light bulb with a standard E26 Edison screw base

The double-contact Bayonet Cap (N.B. the bulb shown is actually a CFL.)

Most domestic and industrial light bulbs have a metal fitting (or lamp base) compatible with standard sockets. 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.

Screw 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 actual bulb glass diameter are in eighths of an inch.) There are four standard 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.
• There is also a rare "admedium" size (E29), incompatible with standard and used to frustrate thieves of bulbs used in public places; and a very miniature size (E5) generally used only for low-voltage applications such as with a battery.

The largest size E39 is now only used in large street lights, although a few high-wattage household lamps (such as a 100/200/300-watt three-way) use it as do 300, 500, 750, 1000 and 1500 watt light bulbs. MES bulbs for 12 volts are also produced for recreational vehicles. Large outdoor Christmas lights use an intermediate base, as do some desk lamps and many microwave ovens. Emergency exit signs also tend to use the intermediate base.

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 or BA designation. These are also extremely 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. BC or B22 or B22d or double-contact bayonet cap, used in Australia, India, Ireland, New Zealand and the UK for most 220–240 V mains lamps. A miniature baynet is used in North America for appliances such as sewing machines and vacuum cleaners.

Pin base

Halogen bulbs are available with a standard fitting, but also come with a pin base, with two contacts 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 halogen bulbs come in a tube, with blades or dimples at either end.

Special lamp bases

There are also various odd fittings for projectors and stage lighting instruments. Projector lamps^[21], in particular, may run on odd voltages (such as 82), perhaps intended as a vendor lock-in or to optimize light output for a particular optical system.

Tubular lamps such as R7S-75 for halogen lamptubes, in this case a 7 mm diameter socket with 75 mm tube length.^[22]

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 V ¹⁶
• Color temperature is approximately proportional to V ^{0.42 [23]}

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 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.

The relationships above are only valid for a few per cent 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.^[24]

In flood lamps used for 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 °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 trade-off 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

Closeup of a tungsten filament inside a halogen lamp

Approximately 92%-95% of the power consumed by an incandescent light bulb is emitted as heat, rather than as visible light. ^[25] For a given quantity of light, an incandescent light bulb, with 5% efficiency, produces more heat (and consumes more power) than a fluorescent lamp (with 7%-15% efficiency) 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.

Quality halogen incandescents are closer to 9% efficiency, 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. Halogen lamps get hotter than regular incandescent lamps because the heat is concentrated on a smaller envelope surface, and because the surface is closer to the filament. This high temperature is essential to their long life. Most safety codes now require halogen bulbs to be protected by a grid or grille, or by the glass and metal housing of the fixture to prevent ignition of draperies or flammable objects in contact with the lamp. Similarly, in some areas halogen bulbs over a certain power are banned from residential use.

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.^[26] 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 incandescent bulb, and several idealised light sources. A similar chart in the article on luminous efficacy compares a broader array of light sources to one another.

A 100 W bulb for 120 V systems, produces 17.5 lumens per watt, compared to a theoretical "ideal" of 242.5 lumens per watt 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 [sic] is 95 lumens per watt."^[28] No known material can be used as a filament at this ideal temperature, which is hotter than the sun's surface.

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 useable for illumination. By careful selection of which eletron energy level transitions are used, the spectrum mitted can be tuned to the spectrum most suitable for visible light.

Proposals to outlaw

The intent of banning incandescent light bulbs is to save electrical energy. These proposals have met criticism due to perceived shortcomings of CFLs (Compact Fluorescent Lamps) including consumer safety, environmental issues (CFLs contain small amounts of the toxic element mercury), the emission spectrum of fluorescent lamps, slow cold-weather starting, the increased costs of replacement, and the higher cost of dimmable fluorescent lamps.^{[citation needed]}

In Canada, electrical regulations now require the use of LED lamps in electrically-illuminated emergency exit signs. Since these are continually illuminated and there may be many signs in a building, the cumulative energy saving is significant. In traffic-signal applications, LED lamps replace incandescents. LED lamps can inherently produce lighting of the saturated colors required for signals, eliminating the energy wasted by filtering the white light of an incandescent lamp.

The United States of America

California will phase out the use of incandescent bulbs by 2018 as part of bill by California State Assembly member Jared Huffman (D-Santa Rosa) that was signed by California Governor Arnold Schwarzenegger on October 12,2007. The bill also requires a reduction in lighting electricity usage.^[31]

Legislation has also been proposed in Connecticut by state Representative Mary M. Mushinsky (D-Wallingford).^[32][33]. On February 8 2007, New Jersey Assemblyman Larry Chatzidakis introduced a bill that calls for the state to switch to fluorescent lighting in government buildings over the next three years. "The light bulb was invented a long time ago and a lot of things have changed since then," said Chatzidakis. "I obviously respect the memory of Thomas Edison, but what we're looking at here is using less energy.^[34] Much of East and Southeast Nebraska, home to 2 million people, has been using fluorescent bulbs in nearly all buildings for decades because of high electricity prices. Arkansas has been using them as primary lighting sources in homes since the World War II era. Because of this legacy, there seems no reason to put any ban on incandescent bulbs in Nebraska, as very few are in use anyway. ^{[citation needed]}

Australia and New Zealand

On February 20, 2007, the Federal Government announced that by 2010, incandescent light bulbs would be banned in Australia. It is estimated greenhouse gas emissions will be cut by 800,000 tonnes (Australia's current emission total is 564.7 million tonnes), a saving of approximate 0.14%^[35]

In response, New Zealand is considering similar measures. Climate Change Minister David Parker said: "The Australians are talking about looking at banning ordinary lightbulbs in three years' time...I think by the time that is implemented in Australia - if it is - we will be doing something very similar".^[36]

Canada

In April 2007, Ontario's Minister of Energy Dwight Duncan announced the provincial government's intention to ban incandescent light bulbs by 2012. The plan would ban the sale of incandescent light bulbs, but not the use.^[37]

The Provincial government of Nova Scotia, Canada would also like to move towar