Origin of Tritium Exit Signs

The Origins of Tritium Exit Signs

Ever since their inception, exit signs were already primed for an overhaul. That is because the first designs of an exit sign were not particularly useful. In order for it to work properly, an exit sign must remain illuminated during blackouts and other conditions which might reduce the visibility in a room. The original signs used incandescent light bulbs which were not able to offer this feature. They were eventually changed with LED signs. These ones still used the same electrical power supply as the incandescent ones, but they used so little power compared to the first ones that they could easily be powered for another hour or so by a small battery backup installed in the sign itself.


That was a significant improvement, but it still depended on a power supply most of the time. The ultimate goal would be to create a self-luminous sign that is safe to use and made with materials that are relatively cheap. The answer came in the form of tritium exit signs.

Technology of Tritium Exit Signs

As it stands, tritium is an isotope of hydrogen. Its molecules are in constant movement, which makes the isotope unstable or radioactive. This might sound dangerous, but it has such a low level energy that in doses used in exit signs it is harmless. In nature, it is one of the rarest materials on Earth, so it would be puzzling how it can be used to make cost effective exit signs. However, its safety and the fact that only a small amount is needed to power an exit sign make it the ideal component to use for self-luminous exit signs.

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Reasons for Tritium Exit Signs

The need for tritium came from the search for a material that could replace radium. Radium was used before tritium as a self-luminous material. However, studies have shown a link between radium exposure and bone cancer, so it has been banned from use in most countries around the world. Consequently, the idea of self-luminous signs was too tempting to pass up, but a new radioactive isotope was needed. Tritium fit the bill perfectly.

Development of Tritium Exit Signs

Experiments were conducted with tritium to make sure that it is safe for use, unlike its predecessor. Once it has been deemed safe, other experiments were conducted to see what the reaction was when particles of tritium went in contact with other elements. Research showed that electrons caused by the decay of the tritium nucleus produced and maintained illumination once they were in contact with phosphor.

Once this was discovered it was relatively easy to develop a method for the two to produce light in an exit sign. All that was needed was a tube that contained the tritium, which was also coated in a layer of phosphor. When the decaying process began, beta particles were released which made the tube glow because of its phosphorous coating. The result is an exit signs that is self-reliant and does not need any external power sources, which can maintain a constant illuminating reaction for up to 20 years.

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