Light bulb

The electric light bulb uses a glowing wire filament heated by electrical resistance to white heat to generate light (a process known as thermal radiation). The 'bulb' is the glass enclosure which keeps the filament in a vacuum or low-pressure noble gas (or halogen gas in the case of quartz-halogen lamps: see below).

The invention of the light bulb is often attributed to Thomas Alva Edison. In fact Edison was just one of many who contributed to the development of a truly practical device for the production of electrically generated lighting.

In 1801 Sir Humphry Davy, an English chemist, made platinum strips glow by passing an electric current through them, but the strips oxidized too quickly to make a useful lamp. In 1809 he created the first arc lamp, which he demonstrated to the Royal Institution of Great Britain[?] in 1810, by creating a small but blinding arc between two charcoal rods connected to a battery.

In 1820 a British scientist Warren De la Rue[?] enclosed a platinum coil in an evacuated tube and passed an electric current through it. The design was based on the concept that the high melting point of platinum would allow it to operate at high temperatures and that the evacuated chamber would contain less gas particles to react with the platinum, improving its longevity. Although it was an efficient design, the cost of the platinum made it impractical for commercial use.

In 1835 James Bowman Lindsay demonstrated a constant electric light at a public meeting in Dundee. He stated that he could "read a book at a distance of one and a half foot". However having perfected the device, to his own satisfaction, he turned to the problem of wireless telegrahy and did not develop the electric light any further.

In 1841 Frederick de Moleyns of England was granted the first patent for an incandescent lamp, with a design using powdered charcoal heated between two platinum wires.

Joseph Wilson Swan(1828-1914) was a physicist and chemist born in Sunderland, England. In 1850 the British pioneer began working with carbonized paper filaments in an evacuated glass bulb. By 1860 he was able to demonstrate a working device but lack of a good vacuum and an adequate supply of electricity resulted in a short lifetime for the bulb and inefficient light. By the mid-1870s better pumps became available, and Swan returned to his experiments. Swan received a British patent for his device in 1878. Swan reported success to the Newcastle Chemical Society and at a lecture in Newcastle in February 1879 he demonstrated a working lamp that utilized a carbon fibre filament. The most significant feature of Swan's lamp was that there was little residual oxygen in the vacuum tube to ignite the filament, thus allowing the filament to glow almost white-hot without catching fire. From this year he began installing light bulbs in homes and landmarks in England and by the early 1880s had started his own company.

Across the Atlantic, parallel developments were also taking place. On July 24, 1874 a Canadian patent was filed for the Woodward and Evan's Light by a Toronto medical electrician named Henry Woodward and a colleague Mathew Evans, who was described in the patent as a "Gentleman" but in reality a hotel keeper. They built their lamp with a shaped rod of carbon held between electrodes[?] in an glass bulb filled with nitrogen. Woodward and Evans found it impossible to raise financial support for the development of their invention and in 1875 Woodward sold a share of their Canadian patent to Thomas Edison.

Using the Woodward and Evans design Edison utilized a carbon filament that burned for forty hours. Edison continued to improve their design. By 1880 he had a device that could last for over 1200 hours using a bamboo-derived filament.

In Britain, Swan took Edison to court for patent infringement. Edison lost and as part of the settlement, Edison was forced to take Swan in as a partner in his British electric works. The company was called the Edison and Swan United Electric Company. Eventually, Edison acquired all of Swan's interest in the company. Swan sold his U.S. patent rights to the Brush Electric Company in June 1882.

The U.S. Patent Office had ruled on October 8, 1883 that Edison's patents were based on the prior art of William Sawyer[?] and were invalid. Litigation continued for a number of years. Eventually on October 6, 1889, a judge ruled that Edison's electric light improvement claim for "a filament of carbon of high resistance" was valid. Research exposed in "A Streak of Luck" by Robert Conot (1979), shows that Edison and his attorneys hid significant information from the judge. They cut out the October 7-21, 1879 section of a notebook that the judge might have determined showed that they were simply extending Sawyer's (or Swan's) work with carbon "burners" or "rods" in an evacuated glass bulb.

Edison and his team did not find a commercially workable filament (bamboo) until more than 6 months after Edison filed the patent application. The weak and short lived (40-150 hours) carbon filament was eventually superceeded by the tungsten filament. In 1903 Willis Whitnew[?] invented a filament that would not make the inside of a lightbulb turn dark. It was a metal-coated carbon filament. In 1906, the General Electric Company were the first to patent a method of making tungsten filaments for use in incandescent lightbulbs. The filaments were costly, but by 1910 William David Coolidge[?] (1873-1975) had invented an improved method of making tungsten filaments. The tungsten filament outlasted all other types of filaments and Coolidge made the costs practical.

One of the major problems of the standard electric light bulb is evaporation of the filament, leading to narrowing. Where the filament is narrower, electrical resistance is higher (due to the smaller cross-section) and the filament heats up more, increasing the rate of evaporation further at that point. The end point of this process is the failure of the filament.

This problem is addressed in the halogen lamp which is filled with halogen gas. This creates an equilibrium reaction where evaporated filament is chemically re-deposited at the hot-spots, preventing the early failure of the lamp. This allows halogen lamps to be run at higher temperatures which would cause unacceptable low lamp lifetimes in ordinary light bulbs, allowing for greater brightness and efficiency.

The incandescent light bulb is still widely used in domestic applications, and is the basis of most portable lighting (for instance, some car headlamps[?] and electric torches). Halogen lights have become more common in auto headlights and domestic situations, particularly where light is to be concentrated on a particular point. The fluorescent light, has, however, replaced many applications of the light bulb with its superior life and energy efficiency. LED lights are beginning to see increased home and auto use, replacing incandescent bulbs.

Table of contents 1 Standard fittings 2 Efficiency 3 Heat 4 See also

Standard fittings Most domestic and industrial light bulbs have standard fittings compatible with standard lampholders. Common types of fitting are:

• MES or medium Edison screw, used in USA for lamps
• BC or bayonet cap, used in UK for mains lamps

Efficiency Luminous efficiency is defined as the ratio of luminous flux[?] to total radiated flux, and is measured in lumen per watt (lm/W) or as a percentage of 680 lm/W, the efficiency of a monochromatic source of wavelength 556 nm (a yellow-green colour to which the human eye is most sensitive).

A different measure, the overall luminous efficiency, is defined as the ratio of luminous flux to total energy input. This is less than or equal to the luminous efficiency.

Type	lm/W	%
light-emitting diode	0.04-20 [6]
40W tungsten incandescent	12.6 [7]	1.9%
60W tungsten incandescent	14.5 [7]	2.1%
100W tungsten incandescent	17.5 [7]	2.6%
glass halogen	16
quartz halogen	24
tungsten-halogen	18-25 [6]
13W twin-tube fluorescent	56.3 [1]
compact fluorescent	45-60 [4]	15%-32% [3]
xenon arc lamp	30-150 [5]
mercury-xenon arc lamp	50-55 [5]
high-temperature incandescent	35 [2]
ideal blackbody radiator	95 [2]	14% [7]
ideal white light source	242.5 [2]
monochromatic 556nm source	680 [7]	100%

[1] http://www.dgs.state.md.us/lighting/faqs

[2] http://freespace.virgin.net/tom.baldwin/bulbguide

[3] http://www.homefamily.net/consumer/energyefficiency

[4] http://www.coffj.com/veg1/lamp.htm

[5] http://www.pti-nj.com/obb_lamps

[6] http://www.chipcenter.com/eexpert/akruger/akruger044

[7] http://physics.ccri.cc.ri.us/keefe/light.htm

Heat A fluorescent lamp, which is approximately 8 times more efficient than an incandescent lamp, will produce 8 times less heat, assuming the same levels of light from both sources. This is one reason why fluorescent lighting is so popular in commercial spaces.

See also

• Arc lamp
• Fluorescent light
• Lightbulb jokes
• Light emitting diode (LED)
• Neon light[?]
• Timeline of lighting technology