Tritium gas is known to be radioactive that the watch manufacturers are currently using two designation- labels- to make watches. They include the T25, T, and T100.
Some people find the T100 also known as T to glow much brighter than the T25 while others find little difference between these two types.The manufacturers mark the labels on the watches themselves. Both labels have no harmful effects.
The labels never cause any health risks or radiations and the countries where the manufacturing plants are situated highly regulate their 
production. However, before purchasing the watch, it’s advisable you consider checking its source, the production facility and the country of origin.
Technically, T25 simply means that the watch features between 1 and 25 mill curies of radioactive tritium while T100 /T has between 26 mCi and 100 mCi. The manufacturer coats the watches glass tube- vial- with a phosphorescent paint-zinc sulfide- in their color of choice. They then introduce tritium gas into this tubes and they then finally seal it.
As the Tritium gas decays, its electrons stimulate zinc sulfide coating and, therefore, produce a constant glow, which is a light that does not require an ambient light or battery to charge. This glow or decay happens immediately after the sealing of the tube. Most tritium producers advertise that the light inside the tubes has 12 years conservative shelf life and 25 full years. This means that after 12 years the tubes brightness starts to fade, and the glow will end completely in another 12 years.
Selecting the right store that sells the watches
Properly choose the right store to purchase your watch as it will have an impact on exactly what you get. Some watch stores can be a great experience while others can be a painful one.
You should keep in mind that customer experiences will never be equal. Before you purchase a watch and especially if you intend to purchase it from an online store, you should know that good ratings do not mean good services or even products. Start by looking at other similar transactions the store has conducted.
This point is very subjective although it is a good direction towards a better purchase. Then read about the watch seller on other different review forums and ask for opinions from others.
You should also check whether the seller offers manufacturers original warranty. Also, try to communicate with the tritium watch seller as this is exactly what will make or even break the deal. See how they respond.
Do they respond very fast or slowly? A good seller should be very helpful, prompt and should also ready to offer advice on some situations where you may have some concerns regarding the deal.…