Pictures of the Future       Fall 2005

Let there be Light

In twenty years, a form of hightech 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, Wilhelm von Siemens commissioned the chemist Werner Bolton to find new materials for incandescent filaments, because the carbon filament lamps commonly used at the time were real power hogs. The new material that was sought had to resist both melting and vaporization 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: tantalum. 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 meter of tantalum filament wound up skillfully in a glass bulb gave off 25 candelas of light at 220 V.

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 company, which used osmium filaments. 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 tungsten-filament light bulb, which is still widely used today.

Following the successful introduction of the tantalum lamp, Bolton was appointed head of Siemens’ first corporate lab, the "Physics and Chemistry Laboratory," which was the precursor of today’s Corporate Technology (CT). Bolton moved out of the makeshift buildings of the tantalum lab and into a new four-story building on Motardstraße in Berlin. There, he had about 1,000 m² of floor space to work with as he oversaw basic research. Only two years later, however, there was not enough room for light research and plans were made to erect another new building.

Bolton’s patents for creating filaments 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 efficient 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. Today, the tungsten lamp is still the best-selling type of lighting in the world, thanks to the excellent performance 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 activities in the Osram GmbH KG company. The name was derived from osmium and wolfram (tungsten). Since 1978, Osram has been a fully owned subsidiary of Siemensnbsp;AG, and scientists from Corporate Research at Siemens work closely with their counterparts at Osram.

50 years after the tantalum lamp, the central lab at Siemens came up with another revolutionary invention. In the early 1950s, Heinrich Welker discovered III-V semiconductors. These are compounds of trivalent elements, such as gallium, which have three bonding electrons, and pentavalent elements like arsenic or nitrogen. Welker’s co-workers had observed that diodes of doped III-V semiconductors emit light when subjected to a low electrical voltage. The importance of this effect was recognized only twenty years later, however. "Optoelectronics research only got moving when low-voltage indicator lamps of all colors were needed for integrated circuits," says 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 indispensable role in the transmission of telephone conversations via fiberoptic cables. Those who made a major contribution to the development 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 professors; and Claus Weyrich, who now manages Siemens Corporate Technology.

Point-source light-emitting diodes (LEDs) as well as IREDs, which radiate light in the infrared range, are now used in many appliances, from remote controls and standby indicators to designer brake lights (see Pictures of the Future, Fall 2003, A Bright Future). They are currently also providing service as environmentally friendly sources of background 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 200nbsp;lm. That means it’s the brightest LED of its kind in the world, and it literally puts conventional light sources in the shade.

Since the mid-1990s, Siemens and Osram scientists have also been researching the organic relatives of LEDs: organic light-emitting diodes or OLEDs (see (see Pictures of the Future, Fall 2003, Brilliant Plastics). An advantage of OLEDs is that they can be produced in nanometer-thin layers on flexible plastic. They can thus be turned into an electronic newspaper or any sort of flat display screen. Their advantage over today’s LCD monitors is that they deliver a luminescent, contrast-rich image that is equally crisp and clear from all angles. Osram subsidiary Osram Opto Semiconductors already manufactures OLED displays for cell phones, home appliances and car radios, and CT researchers are working on making powerful OLED display panels as part of an EU project. One initial 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 enormous growth in OLEDs. "Increasingly, lighting systems of the future will make use of lighting surfaces," says Karsten Heuser, a lighting researcher at CT who recently moved to Osram.

Osram also offers electronic control systems for optimal use of all light sources. These light managers could be programmed to supplement 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

Werner Bolton
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 laboratory director in the incandescent lamp plant, and from 1905 on as head of the first central laboratory (top right). Between 1902 and 1905 he invented and developed 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.