" ... Glow rings are filled with tritium which is housed in a high-density borosillicate glass shell that measures approximately 5mm. This self illuminating safety device is ideal for marking equipment and personal property. Kit markers can be seen from 30m away and are waterproof to a depth of 30m. Designed to glow for 10 years. ... " -- the halflife of tritium is closer to two years, so ten years is very much a stretch.