Tritium is Expensive!

Cost: $30,000 per gram. 

Gaseous Tritium is also used in self-luminous fire safety signs which offer users the most advantageous life-cycle cost of any permanantly illuminated fire safety sign. Typically having a service life of 10+ years, self-luminous signs need no technical maintenance or spare parts during that time. Being self-powered, they do not require any electrical supply or batteries. They are to be found in heritage buildings, undergound works and cinemas (where the possibility of screen reflection is eliminated) Because they need no electical cabling, they are also particularly useful for temporary signage in construction works.

There are more than two million self-luminous EXIT signs installed across the United States.