For years there has been a critical demand within the sign industry for a book on the structural engineering of signs. This comprehensive text more than meets that demand -- it exceeds it. Sign companies, ...
Let
Fluorescent lamps still rank as the most frequently used light source for illuminated signs, according to ST’s Electric State of the Industry Report (see ST, July 2008, page 87, Table 11a), which says they account for 37.6% of respondents’ illuminated-sign output, as well as the Lighting Survey (see ST, April 2008, page 104, Table 4), which says they account for 39.8%.
Fluorescent lamps require a ballast to start the lamp and control the operating current. For decades, only a few magnetic-ballast models existed, and all operated on the same principle. But, in the past five years, electronic ballasts (manufacturers tout their energy savings) have nearly replaced their magnetic counterparts.
I can’t explain both types’ properties, service and installation requirements in one column. I‘ll cover magnetic ballasts here.
Fluorescent lamps are often called “neon lights,” even if no neon gas is involved. For clarity, I’ll use the colloquial “neon” for cold-cathode tubes, while “fluorescent” substitutes for hot-filament cathode tubes, independent of color and gas fill.
Fluorescent-lamp principles
Fluorescent and argon/mercury-filled lamps share similar operating principles, except for their electrodes. Neon lamps, which bear cold, metal-shell electrodes, require high voltage to start and operate, but fluorescent lamps’ heated, filamentary electrodes often require a rather low starting and operating voltage. This is still higher than the common, 110V, U.S. line voltage, which means a fluorescent tube can’t be connected to the power line directly.
Before a fluorescent tube starts, the electrodes must be heated to approximately 1,400° F so they can release electrons into the gas. This is accomplished by running an electric current through the electrode, which comprises resistance wire. To make the current run through the filament, each electrode must have two connections. Consequently, the tube has four connections.
Contrastingly, a neon tube usually has two connections, because its electrodes don’t need to be heated to operate. Because generating a large amount of light is the fluorescent lamp’s main goal, its operating current is 300 to 800mA, or roughly 10 times a neon tube’s usual operating current. Once this operating current is running through the lamp, the lamp current maintains the electrodes’ operating temperature. This means “preheating” isn’t necessary after the lamp has started.