Radium and Tritium

During the Second World War, the military were searching for something that would illuminate the dials of instruments within the cockpits of aircraft that would allow the pilot to read them but not light up the cock-pit and make the plain visible to the enemy at night. The solution that was adopted by many air forces was to paint the figures of the dials with paint that contained either Radium or Tritium. This paint was also used on the faces of watches worn by service men that needed to tell the time in the dark.