For those of you that work in an industrial or heavy commercial setting - places like loading docks, warehouses, R&D, construction, aviation, heavy freight - SL signs can be a cost-saving alternative to industrial sign models. They can even be placed in locations where flammable materials are present.
Hard work is accomplished every single day in industrial environments. It's common to see scuffed walls, layers of paint on the deck, and things getting broken -- a lot! Thermoplastic exit signs are definitely the cheapest exit solution, but they will not last in these businesses.
Self-luminous exit signs are much simpler in design, and have no electronics to disrupt. This means they can sustain more abuse while continuing to serve their purpose.
Any space that is required to have a 'Class' and 'Division' number described by OSHA and the NEC are considered hazardous, due to the presence of explosive elements in the air. Such spaces are commonly found in petroleum refineries, aircraft fueling hangars, dry cleaning plants, grain elevators and coal preparation plants.
LED signs are forbidden by federal law in any location classified by one of the three hazard classes,. Any electronic device in these locations must have a completely sealed housing that prevents the circuitry from interacting with flammable gases, vapors or dust. Exposed electronics like LED signs are capable of electrically sparking an explosion!
If there is spotty or uneven lighting in you interior that would negate the purchase of glow in the dark models, go with SL luminaries.
They use a hydrogen gas called tritium which naturally glows bright. Depending on the model you purchase, you can get an exit sign that lasts a decade or one that will operate for the next 25 years, with several lifespan options in between.