Tritium radioluminescence

[2] During manufacture, a length of borosilicate glass tube that has had the internal surface coated with a phosphor-containing material is filled with tritium.

[4] Some of the colors that have been manufactured in addition to the common phosphors are green, red, blue, yellow, purple, orange, and white.

The GTLSs used in watches give off a small amount of light: Not enough to be seen in daylight, but visible in the dark from a distance of several meters.

[citation needed] These light sources are most often seen as "permanent" illumination for the hands of wristwatches intended for diving, nighttime, or combat use.

They are favored by the military for applications where a power source may not be available, such as for instrument dials in aircraft, compasses, and sights for weapons.

The electrons emitted by the radioactive decay of the tritium cause phosphor to glow, thus providing a long-lasting (several years) and non-battery-powered firearms sight that is visible in dim lighting conditions.

Though these devices contain a radioactive substance, it is currently believed that self-powered lighting does not pose a significant health concern.

A 2007 report by the UK government's Health Protection Agency Advisory Group on Ionizing Radiation declared the health risks of tritium exposure to be double that previously set by the International Commission on Radiological Protection,[8] but encapsulated tritium lighting devices, typically taking the form of a luminous glass tube embedded in a thick block of clear plastic, prevent the user from being exposed to the tritium at all unless the device is broken apart.

[9] According to a report by the OECD,[10] any external radiation from a gaseous tritium light device is solely due to bremsstrahlung, usually in the range of 8–14 keV.

Given that the half-value thickness of 10 keV photon radiation in water is about 1.4 mm, the attenuation provided by tissue overlaying blood-forming organs is considerable.

This results in the absorption of the emitted radiation in a small region of the body, again due to the low penetration depth.

The biological half-life of tritium – the time it takes for half of an ingested dose to be expelled from the body – is low, at only 12 days.

that contain small amounts of tritium are under the jurisdiction of the Nuclear Regulatory Commission, and are subject to possession, distribution, and import and export regulations found in 10 CFR Parts, 30, 32, and 110.

Luminous products containing more tritium than needed for a wristwatch are not widely available at retail outlets in the United States.