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A Short History of Electric Light
by Frank Andrews
The main type of electric lighting other than incandescent filament and carbon arc is that produced by electric gas-discharge. Much experimentation was done in this field during the 18th and 19th centuries. Germans Heinrich Geissler and J. Pl?cker produced a bright violet light from an evacuated tube using an induction coil. Crookes and others continued this work adding other gases to produce different effects. The first practical lamp was the Moore tube introduced in about 1900. The Cooper-Hewitt Mercury vapour lamp, forefather of the modern fluorescent tube, was introduced in 1901. In 1907 French physicist George Claude demonstrated the first neon tube.
American D McFarlan Moore first introduced a high voltage discharge lamp in 1896. This consisted of a tube containing nitrogen giving a pinkish light, or carbon dioxide producing a near daylight colour, and excited by electrodes of metal foil wrapped around the ends. A transformer was used to obtain the several thousand volts needed to cause the light discharge. These tubes were made very long to obtain the greatest efficiency and lengths of 150 feet were not uncommon. In 1898 a chapel in Madison Square Gardens, New York, was lit with Moore tubes. The size of the lamps made them impractical for ordinary home use but their use continued up until the 1940’s in a limited way. In 1902 the external electrodes were replaced by more efficient internal graphite electrodes. Moore also developed an automatic gas feed, to replace the gases absorbed by the glass walls, driven by the lamp current.
First demonstrated by Peter Cooper-Hewitt in 1901. A glass or quartz tube from which the air had been evacuated with an iron electrode at each end and a small quantity of mercury in a bulb at one end. To start the lamp it had to be tilted enabling the mercury to flow to the other end completing the circuit. The current passing through the mercury caused some of it to vaporise and when the tube was straightened again the flow of current continued through the mercury vapour. With the current flow the mercury vapour became incandescent and gave off an intense bluish white light. A green light could be produced when made with uranium glass. Glass is suitable for small mercury vapour lamps but due to the high heat levels in larger ones quartz glass, often encased in a flint glass tube to filter Ultra Violet radiation, had to be used for the larger lamps. Cooper-Hewitt’s lamps were not very successful and became obsolete when gas filled tungsten filament lamps were developed. In the late 1930’s they reappeared greatly improved as the tubular fluorescent lamp. The development was pioneered by three German scientists, Friederich Mayer, Edmund Germer and Hans Spanner. They introduced pre-heating and a fluorescent coating in 1926 which gave a higher light output and allowed the lights to operate on a lower, but still high, voltage. Oxide coating of the electrodes in 1932 brought the voltage required down to a practical level and in September 1935 the first tubular fluorescent lamp was introduced in Cincinnati USA by the American company General Electric Company. The final form of this lamp was developed by Andr? Claude, a cousin of George Claude, in Paris who sold his 1932 patent rights to the American company. Its first major installation was at the US patent office in Washington USA in November 1936. In 1938 it was put on sale to the general public. Osram introduced their fluorescent lamp in 1936. <$IPhilips (Holland)>Philips started to produce the lamps in 1938 but European production was halted for the duration of the war. In 1942, Englishman A. H. McKeag discovered the fluorescent properties of calcium and strontium which doubled the efficiency. Peter Ranby discovered fluorescent halophosphate in 1950 which when used in a fluorescent tube gives a pure white light.Philips introduced a lamp based on colour television technology in 1973 that gave a 50% increase in efficiency and superb colour rendering. The latest development was the small bulb fluorescents introduced in 1980. These are marketed as a replacement for tungsten bulbs.
In 1907 Carl von Linde and George Claude found a commercial method of separating the component gases of air and making inert gases available to the electric light industry. They demonstrated a neon light for the first time in Paris during 1907. Various types of discharge lighting could then be developed, different gases giving different colours. Neon - Red, Argon - Mauve, Helium - Ivory White or Yellow with special glass, Krypton - Light blue, Nitrogen - Buff, Carbon dioxide - Daylight white, Magnesium - Grass Green, Xenon - dark blue, Sodium - Yellow. These discharge lights have been used for advertising purposes since the 1930’s. Piccadilly Circus installed its famous neon adverts in 1932. Modern neon tubes are coated internally with fluorescent powders giving a larger colour range and brighter light. In about 1950 Philips produced a range of neon devotion lamps. These were standard bulb size and contained electrodes shaped as crosses, the Star of David and Muslim symbols. Osram produced a bulb sized neon with a beehive shaped wire spiral electrode which was marked ‘OSGLIM’. Other shapes of electrode can also be found. The neon indicator common in most homes has a life of 80,000 hours making it one of the longest lasting electric light sources. Modern neons often include fluorescing coatings for increased output and colour range. Bulbs are also found with a small neon tube suspended over an ordinary tungsten filament, these were probably used for precision colour matching applications.
Developed from the Cooper-Hewitt lamp by R. K?ch and T. Rechinsky in 1906. These had a quartz tube containing mercury vapour at a normal air pressure and ran at a high temperature. Like the Cooper-Hewitt lamp they were started by tilting but gave a much more intense light. The difficulties of sealing the lead-in wires into quartz prevented them becoming of importance at first. Westinghouse marketed one as the ‘Silica’ lamp in 1908. The Dutch firm Philips solved the lead-in sealing problem in 1935 and also increased the pressure by ten times. With the development of fluorescent powders this form of lamp has remained in popular use for high intensity applications. The most recent development of this type of lamp is the Metal-Halide lamp. This was developed by G. H. Reiling in 1961, using halogens of various metals with the mercury vapour filling giving both increased output and improved colour.
Pioneering work was done by Americans A. Compton and C. C. van Voorhis and Germans E. Lax and M. Pirani in the early 1920’s. Sodium lamps needed a Borate glass, developed by A. H. Compton, to resist corrosion and were filled with sodium vapour. They needed a lower running temperature and gave off an intense yellow light. To maintain the temperature early lamps were encased in double walled evacuated bulbs. Most of this type of lamp were, and still are, produced by Philips and were first introduced in 1931. Their main use is for street lighting.
These give a high-output of heat and are tungsten filament lamps. Designed to work at a lower temperature part of their light output then appears in the infra red portion of the spectrum, although there is still a bright light in the visible part of the spectrum. There is an internal paraboloid reflector, the front of the bulb may be frosted or coloured red. These lamps are nearly 90% efficient energy converters, the standard open wire heating element is only up to 50% efficient. Many discharge and fluorescent forms of light need an external circuit in order to either start them or maintain a steady operation. The filament bulb does not.
There are a huge variety of bulbs developed for very specialised uses but the most commonly found are for photographic use. Early photographic flashbulbs were standard size bulbs but filled with either magnesium tape or wire and usable just once, these were still available in recent years for professional use. A more compact version was developed for snap-shot use. Special floodlight and printing process lights with very accurate colour rendition and usually in high wattages are also common.
The LED has become a common feature on much domestic equipment, largely replacing small bulbs as indicators. Available in a red, green and yellow these light sources operate at 2 to 5 volts and consume from 5 to 40 milliamps. The emitting material is either gallium phosphide or gallium arsenide. Neon indicators are also produced for low voltage but are mainly used for mains voltage use.
The mystery of electricity led to a section of the medical world adopting it as a form of treatment for various illnesses. The light bulb was quickly included into this dubious medicine chest. The role of electricity was as a curative agent and the use of the light bulb was as a therapeutic agent. Heat and Ultra-Violet were regarded as the primary medical features of light.
Heat had always been used and the light bulb was considered a convenient source. After the introduction of Tungsten and other metal filaments, the medical world still preferred Carbon filaments as they produced more heat. In the 1920’s carbon bulbs of the same design as those used in the last century were still being made for medical uses. It is probable that these bulbs were being made by smaller factories, also they are likely to have survived in greater numbers than the earlier carbon bulbs. They were used singly in reflectors to concentrate the heat and in large, wooden, glass lined ‘Light Baths’ containing forty to fifty lamps. The patient would sit in the light bath with his head exposed in a temperature of about 100° Fahrenheit for 15 to 30 minutes. Folding canvas light baths were also used.
As the sun was rich in ultra-violet light it was felt that the ultra-violet light from the arc lamp, and later the Sodium lamp, must possess some therapeutic value. Although it was admitted the workings were not understood, it was believed to have some positive effect on health after thousands of results had been observed. Tuberculosis was felt to respond well. In one trial a success rate of 53% for tuberculosis of the larynx was claimed, better than other known methods. In this case the 100 patients were not supported by conditions of comfort and nutrition. Mercury Vapour lamps were tried but found to be less effective as well as very fragile due to the free moving mercury in the tubes. Arc lamps had a spectrum close to sunlight but with more infra-red. Water coolers had to be incorporated in the reflectors to absorb some of this heat. With the development of nickel cored carbons the spectrum was even closer to sunlight and produced less heat. In addition to tuberculosis ultra-violet light was believed to be useful for skin conditions of all kinds and for rickets. By using ‘Speculae’ to guide the light it was also used for internal treatment in the ears, throat, nose and vagina. Now the laser beam has been harnessed widely for both surgical and cosmetic functions. Laser beams have even made the removal of tattoos easier.
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