What color does xenon emit in a vacuum when excited by an electrical charge?

Xenon was discovered by Scottish chemist William Ramsay and English chemist Morris Travers in July 1898 at the University College London.

Their discovery came about when an industrialist, Ludwig Mond, gifted the team a new liquid-air machine. With the new machine, they extracted more krypton from liquid air. Then, they repeatedly distilled the krypton and isolated a heavier gas. They examined this gas in a vacuum tube and saw that it emitted a beautiful blue glow. They categorized the new gas as inert and called it xenon, derived from the Greek "xenos," which means stranger.

Xenon is a trace gas found in the Earth's atmosphere at about one part in 20 million. This makes it very rare. This noble gas can also be found down on Earth. Some mineral springs emit xenon. Companies obtain the gas for commercial use from industrial plants that extract the gas from liquid air.

The gas has many uses. Xenon lamps illuminate better than conventional lights. For example, stroboscopic lamps, photographic flash lamps, high-intensive arc-lamps for motion picture projection and sunbed lamps all use this gas. Some vehicle headlights use xenon. If you see headlights that give off a soft blue glow, they are probably made with xenon.

The gas has other uses, too. It is used in nuclear energy plants and for filling television and radio tubes. Silicon microprocessors are etched with xenon difluoride. Xenon ion propulsion systems keep some satellites and other spacecraft in orbit.