Photo luminescent Exit Signs, for example, are illuminated via the action of photo luminescence. Energy in the form of light is absorbed by the special coating and stored in much the same way as a “glow-in-the-dark” toy. This stored energy is then re-emitted as light, making the light “glow”. Exit Signs for doors and corridors should be mounted with the bottom of the exit no more than 80 inches (6’8″) above the top edge of the egress opening. Floor proximity exit signs require the bottom of the sign be mounted no less than 6″ from the floor and no more than 18″ above the floor.