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100 years of light research. In 1905, light research at Siemens con- centrated on the tantalum lamp (below); today it fo- cuses primarily on organic light-emitting diodes (OLED, right) for mobile terminals and their bright white LED relatives (far right).


Over 100 years ago, Siemens researchers created the first reliable lamp to use an incandescent filament. Today they are still helping to chart the way toward innovative lighting systems.

I n twenty years, a form of high- tech wallpaper could act as a light source and a television at the same time. Electronic controls would then automatically activate pleasant background lighting or display a TV show, video link or Web page on a large screen. This vision is not far from realization, thanks largely to research activities at Osram and Siemens.

Siemens researchers have been pioneers in lighting technology for well over a century. Back then, Wil- helm von Siemens commissioned the chemist Werner Bolton to find new materials for incandescent filaments, because the carbon fila- ment lamps commonly used at the time were real power hogs. The

new material that was sought had to resist both melting and vaporiza- tion at high temperatures and, above all, it had to be capable of being worked into filaments. Bolton opted for a metal that was then practically unknown: tanta- lum. In his first experiments in spring 1902, he managed to bring it to an incandescent state for long periods, and he was also able to make hair-thin, flexible filaments in an electric-arc furnace. One me- ter of tantalum filament wound up skillfully in a glass bulb gave off 25 candelas of light at 220 volts.

This lamp was about twice as efficient as the carbon-filament lamp and more robust than the metallic-filament lamps of the

Deutsche Glasglühlicht AG com- pany, which used osmium fila- ments. The tantalum lamp entered the market in 1905, and millions of them were sold in the years that followed. It is considered a direct predecessor of the tung- sten-filament light bulb, which is still widely used today.

Following the successful intro- duction of the tantalum lamp, Bolton was appointed head of Siemens’ first corporate lab, the “Physics and Chemistry Labora- tory,” which was the precursor of today’s Corporate Technology (CT). Bolton moved out of the make- shift buildings of the tantalum lab and into a new four-story building on Motardstraße in Berlin. There,

he had about 1,000 square meters of floor space to work with as he oversaw basic research. Only two years later, however, there was not enough room for light re- search and plans were made to erect another new building.

Bolton’s patents for creating fil- aments from metals with high melting points were the clincher in the patent negotiations that Siemens & Halske conducted with the General Electric Company. The Americans had the ability to create filaments from tungsten, which has an even higher melting point than tantalum and attains a more effi- cient state of incandescence, but they were not inclined to dispense with Bolton’s methods. The parties




quickly reached an agreement, and as early as 1913, Siemens produced 16 million incandescent lamps with tungsten filaments. To- day, the tungsten lamp is still the best-selling type of lighting in the world, thanks to the excellent per- formance it delivers relative to its cost. Fifteen billion light bulbs of this kind are sold every year.

In 1919, Siemens & Halske, Deutsche Glasglühlicht AG and AEG combined their lighting-related ac- tivities in the Osram GmbH KG company. The name was derived from osmium and wolfram (tung- sten). Since 1978, Osram has been a fully owned subsidiary of Siemens AG, and scientists from Corporate Research at Siemens work closely with their counter- parts at Osram.

Fifty years after the tantalum lamp, the central lab at Siemens came up with another revolution- ary invention. In the early 1950s, Heinrich Welker discovered III-V semiconductors. These are com- pounds of trivalent elements, such as gallium, which have three bond- ing electrons, and pentavalent ele- ments like arsenic or nitrogen. Welker’s co-workers had observed that diodes of doped III-V semicon- ductors emit light when subjected to a low electrical voltage. The im- portance of this effect was recog- nized only twenty years later, how- ever. “Optoelectronics research only got moving when low-voltage indi- cator lamps of all colors were needed for integrated circuits,” says

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Walter Heywang, who managed the corporate research department at Siemens from 1976 to 1987. In addition, the Siemens researchers realized that III-V semiconductors like gallium arsenide could be used as material for semiconductor lasers. These now play an indispen- sable role in the transmission of telephone conversations via fiber- optic cables. Those who made a major contribution to the develop- ment of semiconductor lasers and light sources included Heywang himself; Günter Winstel, the head of the Solid State Electronics unit; Winstel’s colleagues Karl-Heinz Zschauer and Markus Amann, who both later became university pro- fessors; and Claus Weyrich, who now manages Siemens Corporate Technology.

Since the mid-1990s, Siemens and Osram scientists have also been researching the organic rela- tives of LEDs: organic light-emitting diodes or OLEDs (Pictures of the Fu- ture, Fall 2003, p. 45). An advan- tage of OLEDs is that they can be produced in nanometer-thin layers on flexible plastic. They can thus be turned into an electronic newspa- per or any sort of flat display screen. Their advantage over today’s LCD monitors is that they deliver a lumi- nescent, contrast-rich image that is equally crisp and clear from all an- gles. Osram subsidiary Osram Opto Semiconductors already manufac- tures OLED displays for cell phones, home appliances and car radios, and CT researchers are working on making powerful OLED display pan- els as part of an EU project. One ini-

tial success has been an OLED tile that gives off bright white light. When the tile’s service life and brightness are further improved, market researchers expect enor- mous growth in OLEDs. “Increas- ingly, lighting systems of the future will make use of lighting surfaces,” says Karsten Heuser, a lighting re- searcher at CT who recently moved to Osram.

Osram also offers electronic control systems for optimal use of all light sources. These light man- agers could be programmed to sup- plement incident daylight or create special lighting effects. And maybe one day a system of this kind will still switch on a light bulb here and there — which will by then have cult status as a collector’s item from

times past.

  • Andrea Hoferichter

Point-source light-emitting diodes (LEDs) as well as IREDs, which radiate light in the infrared range, are now used in many appli- ances, from remote controls and standby indicators to designer brake lights (Pictures of the Future, Fall 2003, p. 38). They are currently also providing service as environ- mentally friendly sources of back- ground lighting for LCD monitors. LEDs consume very little power and have an extremely long service life

  • over 100,000 hours. In June

2005, Osram presented a white LED with a luminous flux of 200 lumens. That means it’s the bright- est LED of its kind in the world, and it literally puts conventional light sources in the shade.



Born in 1868 in Tbilisi, Georgia. Chemistry studies in Berlin and Leipzig. From 1892 until his death in 1912, he worked at Siemens & Halske in Berlin, first as labora- tory director in the incandescent lamp plant, and from 1905 on as head of the first central labora- tory (top right). Between 1902 and 1905 he invented and devel- oped the Tantalum lamp, the first metallic-filament lamp. By 1914, fifty million lamps had been manufactured worldwide using Bolton’s methods, about half of them at Siemens.

Wilhelm von Siemens deserves credit for giving Werner Bolton his unquestioning support. For it wasn’t just tantalum filaments that Bolton made white-hot; he often got the personnel depart- ment fired up as well because of his tardiness. Sometimes he didn’t show up for work at all be- cause of his superstitious nature. His co-worker and successor Hans Gerdien once said that “The PCL (Physics and Chemistry Labo- ratory) had a passenger-operated elevator whose door lock could be activated at every floor with a square wrench. If Bolton didn’t succeed in inserting this wrench into the square hole before the moving elevator reached the third floor, that was a very bad omen. After a word of greeting to me, he would say something like, ‘I won’t manage anything at all today,’ and then go home.”

Pictures of the Future | Fall 2005


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