As batteries improved, so did the amount of time that a fixture could remain lit on batteries. Modern systems are lightweight, can be installed virtually anywhere, and are integrated into the fixture, rather than requiring a separate box.
Early battery-backup systems were big, heavy, and costly. In the event of a power outage, the battery would supply power to light the sign. Under normal conditions, the exit sign was lit by mains power and the battery was maintained in a charged state. The sign was still only useful as long as mains power remained on.Īs battery-backup systems became smaller and more efficient, some exit signs began to use a dual-power system. Being larger than its predecessors, this version of the exit sign solved some of the visibility problems. The problem was partially solved by using red-tinted bulbs instead.īetter signs were soon developed that more resembled today's modern exit sign, with an incandescent bulb inside a rectangular-shaped box that backlit the word "EXIT" on one or both sides. The biggest problem was that the exit sign was hardly distinguishable from an ordinary safety lighting fixture commonly installed above doors in the past. In addition, the fixtures could be difficult to see in a fire where smoke often reduced visibility, despite being relatively bright. An inherent flaw with these designs was that in a fire, the power to the light often failed. An exit sign with a design that is easier to see, even in poor visibility, emergency lighting immediately aboveĮarly exit signs were generally either made of metal and lit by a nearby incandescent light bulb or were a white glass cover with "EXIT" written in red, placed directly in front of a single-bulb light fixture.
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