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Krypton

Krypton was named for the Greek "kryptos" meaning "hidden" because it is one of the rarest gases in the Earth's atmosphere. It is colourless and odourless, reacting only with fluorine gas.

In 1960, the wavelength of light in vacuum from krypton's sharp orange-red spectral line was defined as the primary means to realize fundamental unit of length, the metre. This element replaced the previous standard defined by a platinum-iridium alloy ruled bar. Since 1983, the fundamental realization of the unit length metre has changed to be principally based on other wavelengths of light, which are produced by lasers whose frequencies have been measured based on the definition of the second. At the National Research Council Canada (NRC), the Institute for National Measurement Standards maintains the standard of length in Canada. The NRC now uses the spectral line from a helium-neon laser controlled to fall on an absorption line in a molecule of iodine instead of light from a discharge containing the element krypton.

Many fluorescent light bulbs use krypton and argon as a low-pressure filling gas. This gas mixture helps to increase the intensity of the shine and improve the bulb's efficiency. Krypton is also used in flashes for high-speed photography.

This gas is considered non-toxic, but it could potentially asphyxiate by denying the body's access to oxygen.