Put simply, photoluminescence (often referred to as P.L.) is the emission of light from any form of matter after excitation from another light source. Time periods between the absorption and emission can vary greatly from milliseconds to minutes. Similarly, the degree of luminance and its longevity can vary depending on the level of excitation achieved.
The real beauty of photoluminescent products, in the context of a Safety Way Guidance System, is that they do not need electricity to glow in the dark if properly sited and maintained. In an emergency situation where a mains failure has occurred, they will immediately light the way to safety even in smoke conditions.
A photoluminescent fire exit safety sign will look like this is daylight conditions.
But turn off the lights
and it looks like this.
When designing a SWGS you will need to carry out a risk assessment to determine what class of photoluminescent product you require as each class has its own unique charactoristics. For example, if you need your photoluminescent to emit its light quickly and do not need it to glow brightly for more than 20 minutes you may choose Class C product. However, if you need a photoluminescent product that is effective for over 2 hours you may decide to choose a Class G.