Krypton, KRIHP ton, is a chemical element that makes up only about one-millionth of Earth's atmosphere. The British chemists Sir William Ramsay and Morris W. Travers discovered it in 1898. It was named krypton for the Greek word which means the hidden one. Most fluorescent lamps are filled with a mixture of krypton and argon. Krypton is also used in certain electronic tubes, and in luminous sign tubes where a greenish-yellow color is desired.