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The history of light

While "neon tubes" contain no neon at all, they would remain dark without another noble gas. Since the days of gas lamps, artificial lightning has been inconceivable without gases.

Over many millennia, after sunset, humans had to content themselves with the poor lighting provided by dim oil lamps and flickering candles or the light of a campfire. We do not want to include the natural atmospheric oxygen that they needed for combustion among the light gases here, particularly since almost all the energy of the flames is released as heat rather than light. It was only the advent of gases produced and supplied by technical means that enabled the brightness of the artificial source of light to be increased significantly. This was made possible for the first time by burning a gas produced from hard coal, which was widely known and used around the world as “town gas”. The gas lamp was patented in Paris in 1799, with the first gas streetlamps appearing in London in 1807. Town gas was later replaced by natural gas. The end of the 19th century also saw the introduction of acetylene as an illuminating and fuel gas. And it is with this gas that the Messer story began in 1898. Back then, Adolf Messer set up a workshop for the production of acetylene gas generators, which obtain the gas from calcium carbide and water. Fascinated by the beautiful light given off by an acetylene flame, the company founder first fitted such a lamp in his parents’ butcher’s shop. However, he could do nothing to halt the upward march of the electric light bulb.

From filament to electrification

The principle of the glowing filament had been known since 1801. But it took a while longer for it to become everyday technology. Thomas Edison was the first to have his electric light bulb mass-produced with a carbon filament from October 1880 onwards. In the early 1900s, it was discovered that particularly bright filaments can be made from tungsten. However, they only worked well over the longer term if they were protected against oxidation and vaporisation by an inert gas. Because the electric light bulb still had one thing in common with the oil lamp: it produces light through heat. Initial attempts involved the use of pure noble gases, but these were simply not available in sufficient quantity and too expensive for mass production. From 1911, an argon/nitrogen mixture established itself in the market as an inexpensive and effective inert gas. This gas, the coiled tungsten filament and the screw base – the latter also developed by Edison and widely used to this day – became a global recipe for success. The increasing popularity of electric light bulbs went hand-in-hand with the installation of electricity in people’s homes, so the days of gas lighting were numbered. High-quality noble gases came into play again when halogen bulbs – a development from the electric light bulb – came onto the market. Their small glass bulbs are filled with krypton or xenon as well as a halogen component.

Cold gas discharge

In 1857, glass-blower and physicist Heinrich Geissler invented a “cold” light generation principle. His “Geissler tube” became the forerunner of all fluorescent lighting, including energy-saving bulbs. All such bulbs consist of a hollow glass body that is filled with a gas. In most cases, it is a noble gas such as neon or argon, sometimes mixed with mercury or sodium vapour. This gas is ionised by being subjected to a voltage. The separation of ions and electrons results in a gas discharge: the gas begins to glow. This, too, generates heat, but here, for the first time, it is a by-product of the light. Depending on the material the electrodes are made of, the distance between them, the voltage and the operating temperature, there are many different types of gas discharge bulbs. Each gas glows with a different colour, which can also be influenced by the type of glass or its coating. Incidentally, the light produced by neon lamps is by no means pale white – ionised neon emits a rich orange-red. Fluorescent tubes, often colloquially called “neon tubes”, are actually low-pressure gas discharge tubes that are filled with mercury vapour and argon.

The next displacement process

With their ubiquitous light, electric light bulbs and fluorescent tubes have fundamentally changed people’s lives and the appearance of our planet in the 20th century. Yet now they face the same fate that befell gas lights a hundred years ago. The light-emitting diode – better known as LED – has major advantages over conventional lights. It is also leading to the emergence of new players in the light bulb market.

While the traditional products are supplied by a few specialised lighting giants based in Europe and America, LEDs are mainly produced by the Asian semiconductor industry – a light-emitting diode basically being a type of microchip. It consists of a semiconductor material that emits light when a current flows through it. As with other chips, this semiconductor is based on a monocrystalline wafer. This is a thin slice that has been cut from a larger single crystal of silicon or another semiconductor material. The LED represents a completely new level of efficiency in lighting. The tiny size of the light-emitting diodes makes entirely new types of lighting possible, for instance in the form of LED strips that can be attached to any surface. They can last for up to 20 years. In terms of light yield per watt of electrical energy, they have now left all other forms of lighting behind. Until another new physical lighting principle is discovered, the future of artificial lighting no doubt belongs to the LED.

Precise to within 3 ppm

Up to 10,000 LED chips are produced from a single wafer. Further crystal layers of materials with different electrical properties are first applied to this wafer. This is done through crystal growth in epitaxial reactors. The substances from which the crystal structures are formed are supplied to these reactors in gaseous form. Silanes – compounds of silicon and hydrogen with different numbers of atoms, such as SiH4 or Si2H6 – play an important role in this process. The required light emission for the LED chip is achieved by combining certain layers. The choice of materials and structures influences such properties as intensity and colour of the light.

The silanes are introduced into the reactors mixed with pure hydrogen. “Per million parts of hydrogen, there are only 200 parts, or 200 ppm, of silane,” Gary Li, who is responsible for specialty gases at Messer in China, explains. “For the desired crystal growth to be able to take place, the mixture must fulfil the precise specifications. We produce it with a maximum deviation of 3 ppm.” Another gas mixture used for the reactors consists of nitrogen with a silane content of five per cent. The manufacturers give little away about their processes, preferring to keep their know-how strictly protected. “However, we know that a range of other gases are used in addition to these mixtures,” says Li. “Messer also supplies LED customers with high-purity hydrogen, nitrogen, nitrous oxide, helium and argon.”

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