Self Luminous Exit Signs - History
The Emergence of Self Luminous Exit Signs
Prior to 1950, there weren't a whole lot of options when it came to exit signs. On one hand you had bulky electronic exit signs. Unlike the bright, efficient LED signs of today, older signs used incandescent bulbs set behind a semi-opaque plastic or glass exit sign face. Emergency power was provided by batteries located on each floor of the building.
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Incandescent exit signs drew a lot of power, required constant maintenance and relied on a remote emergency energy source that would often become disconnected during fires or floods. Worse yet, exit signs of those times were much dimmer.
World War II was reaching it's end and nuclear technology was advancing rapidly, made possible by Albert Einstein and the prior work of the Curies. This spawned a few different self-powered signs that would eventually lead up to the self luminous technology of today.
Photoluminescent Exit Signs
World War II created the demand for glowing emergency exits in ships, submarines, barracks and bombers where battery power was unavailable. Glow in the dark technology advanced to a point that it could be used in exit sign applications, especially aboard Naval vessels.
The problem was that glow in the dark signs required ambient light to be on 24/7 in order to charge the luminous materials. This negated a significant number of locations, and the Army Corps of Engineers set to patenting a sign that could glow on it's own.
Radium Exit Signs
Before the dangers of radioactive materials were fully known, a new type of self illuminating technology began appearing on the instrument panels of bombers, in time pieces and gunsights. Exit signs soon followed; essentially flat panel signs coated with a paint mixture of radium and copper-dopped zinc sulfide.
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Radioluminescent exit signs required some UV light to power but would last far longer than photoluminescent signs. The problem was that radium fixtures produced lingering radiation that was toxic to humans over a period of time.
Self Luminous Exit Signs
By the 1960's and 1970's, radium painted signs were being phased out due to their hazards. Tritium was discovered as a far better self powered exit sign alternative in the late 1950's. It allowed exit signs to glow completely independent of electricity or UV light sources. They have been a popular fixture ever since.