Self luminous exit signs

We see signs everyday, everywhere. They are there for a purpose, at day time we can see the signs clearly but come night time, it can be difficult. Some signs are very vital to the safety of all people, like a stop sign on a crossroads. Some signs are inside a building, like a fire exit sign. We don't pay much attention to it but it is a very important sign. When there is a fire, and in case the light went out on a regular Exit Signs, what would you do, will you be able to find the exit fast enough or find it before its too late. There are some special Self luminous exit signs that can come in handy on all building. In case of fire and power outage at the same time, it could mean life or death. A self luminous sign doesn't need any power to operate and will work in almost any conditions, plus it saves you some money on electricity bills. Photoluminescent exit signs doesn't cost a fortune and you don't have to add anything extra. This kind of signs are used on most street signs we see in but I haven't seen one inside a building, like for a fire escape sign.