Lighting
Since visibility may be reduced in a fire, due to smoke or failure of electric lighting, the sign is often permanently illuminated, usually by one of:
- Radioluminescence, self-luminous, where a phosphor coating inside a glass tube glows due to the beta decay of radioactive tritium in the tube. Radioluminescence exit signs are prohibited in US Department of Defense installations.
- Photoluminescence ('glow in the dark'), Phosphorescence, where light is absorbed from the surroundings and slowly re-emitted.
- Electric light, with a local rechargeable power source.
- Electric light, with the building's emergency lighting circuits providing back-up power from a UPS and/or a generator in case normal power fails.
Read more about this topic: Exit Sign
Famous quotes containing the word lighting:
“What I like, or one of the things I like, about motoring is the sense it gives one of lighting accidentally, like a voyager who touches another planet with the tip of his toe, upon scenes which would have gone on, have always gone on, will go on, unrecorded, save for this chance glimpse. Then it seems to me I am allowed to see the heart of the world uncovered for a moment.”
—Virginia Woolf (1882–1941)
“Popular art is normally decried as vulgar by the cultivated people of its time; then it loses favor with its original audience as a new generation grows up; then it begins to merge into the softer lighting of “quaint,” and cultivated people become interested in it, and finally it begins to take on the archaic dignity of the primitive.”
—Northrop Frye (b. 1912)
“There is no more miserable human being than one in whom nothing is habitual but indecision, and for whom the lighting of every cigar, the drinking of every cup, the time of rising and going to bed every day, and the beginning of every bit of work, are subjects of express volitional deliberation.”
—William James (1842–1910)