Incandescent light bulb

An incandescent light bulb is a type of electric light that shines by heating a thin wire called a filament. The filament is inside a glass bulb that is empty or filled with special air to stop it from burning. When electricity flows through the filament, it gets bright enough to light up a room or a lamp.

Incandescent bulbs come in many sizes and can work with different amounts of electrical power. They are easy to make and don’t need extra parts, which made them very popular for many years. People used them in homes, offices, cars, and small portable lights.

However, incandescent bulbs are not very efficient. Most of the energy they use turns into heat instead of light. Because of this, they use more energy than newer kinds of lights like compact fluorescent bulbs or LED lamps. Many governments have stopped selling incandescent bulbs to save energy, so they are used less today.

History

Historians Robert Friedel and Paul Israel list inventors of incandescent lamps before Joseph Swan and Thomas Edison of General Electric. They found that Edison's version was the first practical one because it had four important qualities: good material for the light, a very empty space inside the bulb, a design that used power well, and the parts needed for a big lighting system. However, Joseph Swan made his own light bulb before Edison and it was used in London as early as 1881.

Historian Thomas Hughes said that Edison’s success came from making a whole system of electric lighting, not just the bulb. He made sure every part, from the power source to the wires, worked well together. Other inventors made bulbs and generators but their systems weren’t complete, so they are mostly forgotten.

Early pre-commercial research

In 1761, Ebenezer Kinnersley showed how heating a wire could make it glow. But these wires burned out quickly in air. Later, Limelight became popular for stage lighting by heating calcium oxide with a special flame.

In 1802, Humphry Davy used a big battery to pass electricity through a thin piece of platinum, making it glow. It wasn’t bright or long-lasting enough for everyday use, but it inspired others for many years. Davy also showed how two pieces of charcoal could create a bright spark.

For the next 40 years, people tried to make better lighting using carbon rods and special gases. Many tested different metals and designs but nothing worked well for home use.

In 1835, James Bowman Lindsay showed a constant light in public in Dundee, Scotland, saying you could read a book from a distance. But he didn’t develop it further.

In 1838, Belgian inventor Marcellin Jobard made a light bulb with a vacuum and a carbon wire.

In 1840, British scientist Warren De la Rue put a coiled platinum wire in a vacuum tube and passed electricity through it. The design worked but platinum was too expensive for regular use.

In 1841, Frederick de Moleyns of England got the first patent for a light bulb using platinum wires in a vacuum.

In 1845, American John W. Starr got a patent for a light bulb using carbon wires, but it was never made for sale.

In 1851, Jean Eugène Robert-Houdin showed light bulbs on his estate in Blois, France. His bulbs are still kept in a museum there.

In 1859, Moses G. Farmer built a light bulb with a platinum wire. Thomas Edison later saw one of these in a shop and asked Farmer for advice.

In 1872, Russian Alexander Lodygin invented a light bulb and got a patent in 1874. He used two carbon rods inside a glass bulb filled with nitrogen. Later in the US, he used metals like chromium, iridium, and tungsten.

In 1874, Canadian inventors Henry Woodward and Mathew Evans filed a patent for a lamp with carbon rods in a glass cylinder filled with nitrogen. They sold the rights to Thomas Edison in 1879.

Commercialization

Carbon filament and vacuum

Joseph Swan was a British scientist. He started working with carbon wires in glass bulbs in 1850. By 1860, he made a working bulb but it didn’t last long because of air inside and lack of electricity.

By the mid-1870s, better pumps were available and Swan started testing again.

With help from Charles Stearn, an expert in vacuum pumps, Swan in 1878 made a way to stop the bulb from darkening quickly. He got a British Patent in 1880. On December 18, 1878, Swan showed a lamp using a thin carbon rod. It worked for only a few minutes but he showed it again on January 17, 1879, and it worked well. On February 3, 1879, he showed it to 700 people at a meeting. Their building was the first public place lit by electricity. The lamps Swan showed used carbon rods from arc lamps, not thin wires, so they needed thick wires for power and weren’t practical for sale. But they showed that lighting with a good vacuum, carbon, and special wires was possible. This bulb lasted about 40 hours.

Swan then worked on making better carbon wires and attaching them. He treated cotton to make strong thread and got a patent in 1882. From then, he started putting bulbs in homes and famous places in England. His house was the first in the world lit by a light bulb. In 1881, the Savoy Theatre in London was the first theatre and public building lit completely by electricity. The first street lit by these bulbs was Mosley Street in Newcastle, United Kingdom in 1880.

Thomas Edison began researching practical light bulbs in 1878. He filed his first patent on October 14, 1878. After many tests with carbon and other metals, he went back to carbon wires. On October 22, 1879, his first test lasted 13.5 hours. He kept improving and by November 4, 1879, he filed a US patent for a lamp using a carbon wire shaped in a coil. He and his team found that a carbonized bamboo wire lasted over 1200 hours. In 1880, the Columbia, a ship of the Oregon Railroad and Navigation Company, was the first to use Edison’s electric lights — and the first ship to use a dynamo.

Albon Man started the Electro-Dynamic Light Company in 1878. Weeks later, the United States Electric Lighting Company was formed. They put up their first lights in New York City in fall 1880, six months after Edison’s lights on the Columbia. Hiram S. Maxim was the chief engineer at the US Electric Lighting Company. After success in the US, Edison’s bulbs became popular in Europe; the first ones in the Nordic countries were put up at a factory in Tampere, Finland in March 1882.

On March 4, 1880, just five months after Edison’s bulb, Alessandro Cruto made a way to create thin carbon wires by heating platinum wires with alcohol, then removing the platinum at high heat. In 1882 at a big show in Germany, Cruto showed bulbs that were more efficient and gave a whiter light than Edison’s.

Lewis Latimer, who worked for Edison, made a better way to treat carbon wires to stop them from breaking and to shape them. On January 17, 1882, Latimer got a patent for this process, which was bought by the United States Electric Light Company. He also patented other improvements like better ways to attach wires to the bulbs.

In Britain, Edison and Swan’s companies joined to become the Edison and Swan United Electric Company (later Ediswan, then part of Thorn Lighting Limited). Edison was against it at first but had to join. Eventually, he bought all of Swan’s share. Swan sold his US rights to the Brush Electric Company in June 1882.

The United States Patent Office said on October 8, 1883, that Edison’s patents were based on earlier work by William Sawyer and were not valid. There was fighting over this for years. Finally, on October 6, 1889, a judge said Edison’s claim for “a filament of carbon of high resistance” was valid.

In 1893, Heinrich Göbel said he made the first light bulb in 1854 with a thin carbonized bamboo wire, special wires, and a very empty bulb. Courts had questions about this but there was no final decision because Edison’s patent ended. Research in 2007 showed the story about Göbel’s bulbs in the 1850s is made up.

The hardest part was keeping the air out of the bulbs because moisture would break the bulb when lit, and oxygen would damage the wire. In the 1880s, they used phosphoric anhydride with expensive mercury pumps. Around 1893, Italian inventor Arturo Malignani found that phosphorus gas could remove water and oxygen. In 1896 he got a patent for putting red phosphorus inside the bulb as a “getter” to make cheaper bulbs that lasted 800 hours. Edison bought this patent in 1898.

In 1897, German scientist Walther Nernst made the Nernst lamp, a new kind of bulb that didn’t need a vacuum or special gas. It was twice as good as carbon wire bulbs but was replaced by metal wire bulbs.

Metal filament, inert gas

US575002A patent from 1897 by Alexander Lodygin describes wires made of rare metals including tungsten. Lodygin sold the rights to General Electric.

In 1902, Siemens made a tantalum wire for bulbs. It worked better than carbon wires because it could get hotter. But the wires were long and needed support and they broke apart after a few hundred hours. General Electric bought the rights to use tantalum wires and made them in the US until 1913.

From 1898 to about 1905, osmium was used in bulbs made by Carl Auer von Welsbach. It was very expensive so people could bring back used bulbs for credit. It didn’t work for standard voltages so several bulbs were used together. These were mostly sold in Europe.

Tungsten filament

On December 13, 1904, Hungarian Sándor Just and Croatian Franjo Hanaman got a patent for a tungsten wire bulb that lasted longer and gave brighter light than carbon wires. Tungsten bulbs were first sold by the Hungarian company Tungsram in 1904. Filling the bulb with a gas like argon or nitrogen slowed down the tungsten wire’s loss, letting it get hotter and brighter without wearing out as fast.

In 1906, William D. Coolidge made a way to create soft tungsten from compressed tungsten, which could be shaped into wires while working for General Electric Company. By 1911 General Electric sold bulbs with soft tungsten wires.

In 1913, Irving Langmuir found that filling a bulb with inert gas (first nitrogen, then argon) made it twice as bright and stopped the bulb from darkening. He got a patent for this on April 18, 1916.

In 1917, Burnie Lee Benbow got a patent for a coiled coil filament, where a coiled wire is wrapped into another coil using a tool. In 1921, Junichi Miura made the first double-coil bulb using coiled coil tungsten wire while working for Hakunetsusha (a predecessor of Toshiba). At that time, machines to make coiled coil wires didn’t exist. Hakunetsusha made a way to make them in large numbers by 1936.

Between 1924 and World War II, the Phoebus cartel tried to control prices and sales of bulbs outside of North America.

In 1925, Marvin Pipkin got a patent for frosting the inside of bulbs without making them weak. In 1947, he got a patent for coating bulbs with silica.

In 1930, Hungarian Imre Bródy filled bulbs with krypton gas instead of argon and made a way to get krypton from air. Making krypton bulbs started at Ajka, Hungary in 1937, in a factory designed by Polányi and physicist Egon Orowan.

By 1964, making and using bulbs got much cheaper — about thirty times cheaper than when Edison first made them.

The use of incandescent bulbs grew fast in the US. In 1885, about 300,000 bulbs were sold, all with carbon wires. When tungsten wires came, about 50 million homes had bulb sockets. In 1914, 88.5 million bulbs were used (only 15% with carbon wires), and by 1945, 795 million bulbs were sold each year (more than five per person).

Efficacy and efficiency

Further information: Luminous efficacy

Most of the power a light bulb uses makes heat, not light. Only a little bit makes visible light. Some things, like heat lamps, need this heat.

Light bulbs are rated by how much light they make for the power they use. This is called luminous efficacy and is measured in lumens per watt (lm/W).

An incandescent bulb uses more power and makes more heat than most other lights. In buildings with air conditioning, this extra heat can make the air conditioner work harder. However, the heat from lights can help in winter, though it is usually cheaper to heat a building in other ways.

Color rendering

The light from an incandescent bulb looks very much like natural daylight. This makes it good for tasks where color matters, like filming movies.

Cost of lighting

See also: Architectural lighting design

Incandescent bulbs are cheap to buy but cost more over time because they use more energy and don’t last as long. Switching to more efficient lights can save energy and money, even if the new bulbs cost more at first.

Measures to ban

Because incandescent bulbs use more energy, many places have stopped selling them. This helps save money and energy. Some people worry that new bulbs cost more or give worse light, but better lights like LED are now common.

Efforts to improve efficacy

Some companies tried to make better incandescent bulbs. They tried special designs to make the bulb more efficient, but these did not work well enough. New ideas are still being tested, but LED bulbs are now much more efficient.

Construction

Incandescent light bulbs are made of glass that is sealed to keep air out. Inside the bulb is a thin wire called a filament, usually made of tungsten. When electricity flows through the filament, it heats up and glows, making light.

Most bulbs are either clear or have a special coating on the inside to soften the light. Some bulbs are colored by adding different materials to the glass. The bulb may be filled with a special type of gas or left empty (a vacuum) to help the filament last longer and glow better. The filament is connected to the outside world through wires that pass through the base of the bulb.

Manufacturing

Early incandescent light bulbs were made by hand. This was slow and costly. Later, machines were created to make bulbs faster and more cheaply. One important machine was the Westlake machine. It started being used in 1910. It was made by Libbey Glass and helped produce many bulbs quickly.

Corning Glass Works made better machines, like the Ribbon Machine in 1926. This machine could make thousands of bulbs every hour. It moved glass along a conveyor belt and shaped it into bulbs. By the 1970s, these machines made almost all the incandescent bulbs used around the world. The last steps included adding the filament and testing the finished product. The last of these machines in the United States stopped working in 2016 when a factory in Wellsboro, Pennsylvania, closed.

Filament

Carbon was one of the first materials used to make light bulb filaments because it can get very hot. Early filaments were made from carbonized paper or bamboo.

Later, metal filaments were tried. Tungsten, a metal with a very high melting point, became the most common material for filaments. By 1910, a way was found to make tungsten filaments strong and flexible enough for use in light bulbs.

To make the bulbs more efficient, filaments are often made in a coiled shape. This helps the filament last longer and burn hotter, making the bulb brighter.

Filaments can wear out over time because the tungsten evaporates when it gets very hot. To slow this down, modern bulbs are filled with gases like argon or nitrogen, which help keep the filament from evaporating too quickly.

Electrical characteristics

Power

Incandescent light bulbs are simple electrical devices. They use power in a direct way. The power they use is shown on the bulb. For bulbs with the same voltage and type, the one that uses more power will give off more light.

The table shows how much light, measured in lumens, different 120-volt incandescent bulbs give at various power levels. Bulbs with 230 volts usually give a little less light, except for the 25-watt bulb, which may give more. The light from "soft white" bulbs is often a bit less than from clear bulbs at the same power.

Current and resistance

The resistance of the filament in an incandescent bulb changes with temperature. When the bulb is off, its resistance is much lower than when it is on. For example, a 100-watt, 120-volt bulb has a resistance of 144 ohms when lit, but only about 9.5 ohms when it is cold. Because these bulbs are simple electrical devices, special controls called TRIAC dimmers can be used to change their brightness. The bulb reaches most of its brightness quickly, in about 0.13 seconds after being turned on.

Physical characteristics

The filament in a tungsten light bulb is strong when it is cool but can break when it gets hot. If the bulb is hit, the filament might break or melt. Modern bulbs have a special part that stops the electricity if the filament breaks.

Bulbs come in many shapes and sizes, with names like A55 or PAR38. These shapes and sizes follow rules set in different countries. Some bulbs spread light in all directions, while others focus the light forward, like in spotlights. Bulbs also have different bases, such as screw bases or bayonet bases, to fit into different types of light fixtures.

Light output and lifetime

See also: Lamp rerating

Incandescent lamps are very sensitive to changes in the electricity they use. When the electricity is close to what the lamp needs:

• Light you see changes with the electricity used raised to the power of 3.4
• Power used changes with the electricity used raised to the power of 1.6
• Lifetime changes with the electricity used raised to the power of -16
• Color temperature changes with the electricity used raised to the power of 0.42

If you lower the electricity by 5%, the bulb will last twice as long but give less light. Some bulbs, like those used for traffic lights, are made to last longer even if they are not very bright.

The Centennial Light is a special bulb that has been burning since 1901. It gives off only a small amount of light, like a four-watt bulb. There are also stories of other very long-lasting bulbs.

Different bulbs designed for different electricity levels can give different amounts of light. Lower electricity bulbs can give more light for the same power because they have thicker parts inside.