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Neon: creating pictures and words with light

Neon lights create gaudy pictures and spell out brand names on advertisements the world over.

Unlike the traditional electric light bulb, neon lights in the form of thin tubes can easily be shaped into lettering and other intricate outlines.
To produce their distinctive light, they exploit what is called 'electric discharge through gases'. Ordinarily, gases do not easily conduct electricity - they are good insulators. They can, however, be made to conduct electricity if their pressure is lowered and a high voltage is applied.

In the late 19th and early 20th centuries, scientists investigating electric discharge through the rare gas neon at low pressures, first observed the striking red-orange glow the gas gives out.
To create neon light, electricity is applied to the ends of a glass tube filled with neon. Atomic particles called electrons stream from one end of the tube to the other, and on their way they collide with atoms of neon. As a result of the collisions, electrons orbiting within the neon atoms are knocked out of orbit. They acquire extra energy from the impacts, just as a billiard ball acquires energy when struck by another. As they return to their original orbit, they give out their surplus energy as electromagnetic radiation.

This radiation has a frequency which lies in the visible light range and you see it as a brilliant red-orange glow.

When other gases are used in tubes, a similar process occurs. But the electrons give off radiation at different frequencies, which you see as different colours. Helium gives a golden-yellow light and krypton a pale violet. Other colours are produced by fluorescent materials in tubes containing mercury or argon, sometimes in combination with coloured glass.

Neon at night
Dominating the kaleidoscope of neon in Las Vegas is the Pioneer Club's neonised cowboy with his waggling cigarette. The figure was created in 1951. In Hong Kong, too, neon lights bustle in the air. Some of them, such as this dragon figure, are a glass-bender's nightmare.