Whenever a building owner chooses to buy a battery operated exit sign, he or she can select from an array of different colors. That is due to the presence of wiring in such a fixture. That wiring ensures the sign’s ability to electrically charge the chemical mix that fills the designated space within each sign.
Years ago, chemists discovered that when an electrical discharge was applied to a rarified gas, one inside of a glass tube, then that gaseous substance would light up. More importantly, its beams would take on a distinguishing hue. Even the mercury in a barometer could produce a blue glow, if exposed to a sufficient amount of static electricity.
The same phenomenon came to be associated with the discharging of vapors the contained certain salts. In that case, a blue glow indicated the presence of lead, arsenic or selenium. Most copper compounds produced an emerald green color, when exposed to a discharge. Other chemicals produced other hues.
Now the manufacturers of one type of exit sign made use of that fact. The employees working in their plants put wires in their signs, wires that could receive energy from an electrical current. It was understood that a building with lights would have access to a current, one that could be used to power any signage. That current could provide the electrical energy needed for discharging a chemical mix, a vapor in a tube.
However, it eventually became obvious that in an emergency, there was a strong chance that the electrical power could become cut off. That realization motivated development of a battery operated exit sign. The sign’s battery furnishes the needed power, in the event of an emergency. It can keep the sign’s letters glowing for up to 90 minutes, in the event of a blackout.
At no point did the manufacturers give serious consideration to signage that relied totally on batteries. Any such batteries would need to be so large, that any sign able to hold them would look ridiculous, if placed atop a doorway. Still, that was only one of two reasons that the battery operated exit sign came to be called an emergency sign.
Even today, when manufacturers can make very small batteries, not a single manufacturing plant has turned out signage that relies solely on a store of chemical energy. That is because any battery will eventually die out. At that point it must be either re-charged or replaced. No building owner would want to be saddled with the added expense of paying employees to go around and re-charge or replace a series of batteries, notably those found in the building’s exit signs.
Today, manufacturers offer building owners the chance to select from three types of battery operated exit signs. In one type the glowing letters contrast with the clearness of a thermoplastic plate. In the second type the letters’ glow stands out against the background provided by an aluminum cast plate. Both plates exhibit the thinness that allows them to assume an unobtrusive position above a doorway.
The third of the three types of such signage differs from the other two in the nature of the wiring, and in the amount of discharged chemicals. In that third type, only the edges of each letter glow. Therefore, the sign’s wires must only send discharge signals into a tiny segment of that object, notably the edges of its four letters. Of course, the glow coming from the edge of those letters can take on any of the colors that are found in all of the other types of battery operated signage.