Betalight

A betalight is an artificial light source powered by the radioactive decay of tritium (³H) gas.

The betalight consists of a glass container (usually in the form of a slender tube or two fused glass plates) filled with tritium gas. The inside walls of the enclosure are coated with a phosphor. As the tritium decays, it emits Beta particles (high energy electrons). These electrons stimulate the phosphor, causing it to glow.

No external power source is required and the lights are very reliable. This has lead to their broad application in emergency exit signage.

The lifetime of a betalight is limited by the half-life of the tritium gas; the light will glow with exponentially less light through the years, but the service lifetime of betalights is usually quoted as ten to fifteen years.

No external radiation is produced during normal operation, although rupture of the glass capsule will release the radioactive tritium gas contained within. Because of this, used betalights should be returned to their manufacturer rather than being incinerated or landfilled. Manufacturers will often recycle betalights on a one-for-one basis when new betalights are purchased.