When in the market for exit signs, there are a several different types to choose from. You can purchase your standard AC power with battery backup, or you can also purchase a sign with strictly battery power. There are signs powered by tritium, which is a gas, or you can purchase a photoluminescent exit sign. Here's why you should choose the later option.
Photoluminescence works through the absorption of photons. In other words, they are powered by the absorption of light from other sources – essentially, they are glow in dark. They draw power from other light sources and thus can use that power to light themselves up once the area where they are placed is dark, much like solar powered lights. Most photoluminescent exit signs only require five-foot candles of illumination to get enough energy to light up in the dark. The signs are printed on a luminous film, which absorbs the light. So long as you make sure that they are receiving adequate lighting, you should not have any issues with this type of sign.
Photoluminescent exit signs have several power advantages. A power source of any type is not required, either electricity or battery backup. This in and of itself has its advantages – no upkeep cost in battery replacement or electricity costs, and no risk of failing components due to age, water damage, or other stressors. With less risk of damage these types of signs can generally last upwards of 20+ years. Since they don't require a battery backup, that means that you don't have to worry about the battery failing. Because there isn't an electrical or battery-operated power source, they can be used in either wet or dry conditions.
Additionally, they are also good for the environment, as well. There is no use of energy, and you also don't have to worry about any sort of special disposal requirements -There is nothing toxic in the makeup of photoluminescent signs.
The way the signs are made are another bonus. There is no need for them to have any glass casing. This reduces the risk of injury, and the need to replace the sign due to damage.
Photoluminescent signs are more versatile – they can either be hung near the ground or above a doorway with ease. With no power source needed; they can hang directly on a wall without the obstruction of a power or battery box.
While not required by law, photoluminescent lighting meets all requirements for properly lit emergency signage, with UL certification. Beyond the sign itself, it is important that you follow all laws and codes associated with the installation of the signs.