The “working principle” of a trigalight is comparable to that of a conventional television tube.
A very thin coating of luminous substance is applied to a glass surface.
The coating is bombarded with electrons emitted by the tritium gas (H3), which cause the layer to light up (conversion of the electric charge to light).
Whilst in a television tube, the electrons are generated electronically through the use of a cathode, with a trigalight, the necessary electrons are created through the radioactive disintegration of tritium (an isotope of hydrogen)
he disintegration electrons of the tritium have a range of just 1-3 mm in air and can’t even penetrate the human skin. The energy of (at most) 18 keV is not sufficient for this. Thus the disintegration electrons (beta radiation) do not have the power to penetrate or leave the sealed glass vessel of a trigalight.