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Neon and Fluorescents: A Circus of Similarities

When properly manufactured and installed a neon tube can light for decades and it is far more efficient than an incandescent bulb. But it is arguable that the fluorescent won the tube lighting system honor, that it became the illuminating tube du jour.

By Randall L. Caba

Ladies and gentlemen, welcome to the circus of tube lighting similarities! Today we will show for you the parallelisms and yes, the isomorphisms too of two, count them two, tube lighting systems: fluorescent and neon. So grab your peanuts and popcorn, step right up and prepare to be swept away by this tour-le-grandeur high-wire act.

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  • Now folks, did you know it is said that the Father of neon, French scientist Georges Claude, wanted neon to be implemented as a lighting system? He wanted much more than the advertising role it plays today, and why not? When properly manufactured and installed a neon tube can light for decades and it is far more efficient than an incandescent bulb. But it is arguable that the fluorescent won the tube lighting system honor, that it became the illuminating tube du jour. You may be asking, “How so?” Because fluorescents are everywhere. In most every shopping mall, grade school and high school, industrial center, prison and even in neon shops they are the lighting ringmasters. Now, I’ll agree, they are usually ho-hum in body. Nonetheless they are the dominant choice in tube lighting. But neon tubes are unique. They are extraordinary in their handcraft creation, diverse color palette and in the electromechanical way that they light. But doesn’t neon share qualities with the fluorescent? If so, then what are these attractions?

    The make-up
    The classic hot cathode fluorescent used a simple magnetic ballast, a bypass circuit and a starter switch to light. Most interesting is that the starter switch often housed a neon filled bulb. Yes folks, the classic fluorescent system housed neon complete with electrodes as a component. Well all right, the electrodes were two bimetallic strips but don’t let that difference waggle you. When a room’s light switch flipped on, electric current passed through the fluorescent tube cathodes and through a bypass circuit, “the clown walk-around” if you will. It did not pass through the fluorescent tube itself; it was not invited yet. Instead, current flowed through the neon bulb and arced across the bimetal strips. As the bulb lit up it heated and caused the strips to close short-circuiting and turning off the bulb.

    The bulb quickly cooled and the metal strips expanded opening the circuit ­ a slow burn compared to neon. But by this time, current flowing through the tube cathodes heated them enough so that gas in the tube was partially ionized. This effectively reduced electrical resistance posed by the gas fill. All that was needed to light it was a quick bump up in voltage and jackpot! The tube would light. The ballast provided that bump. You see, while the neon bulb was lit, current also passed through the ballast and there like magic, built up a magnetic field. When the bulb short-circuited then the strips opened, the magnetic field collapsed causing a spike in voltage. That high voltage spike shot midway through the fluorescent tube causing it to produce a grand parade of light.

    Modern fluorescent tubes seldom use starter switches instead opting for the rapid-start or instant-start lamp design. The rapid-start innovation drives electrical current through the lamp’s electrodes while maintaining a charge difference between them. The electrodes heat rapidly and cause a pratfall of electrons to light the tube. The instant-start lamp design operates much like a neon transformer in that it ionizes the inert gas fill using high voltage across the electrodes. The ballast drives excess electrons onto each electrode in alternating fashion. Like bumbling, mobbing clowns these extra electrons attempt to play tag with those in the gas fill. But the gas fill electrons trapeze away causing their gas atoms to ionize and throw off light. A neon tube plays much the same way but it does so without heating the electrodes, hence the reason neon is considered cold cathode under the big top.

    The problem with lighting any gas discharge tube is that electric current can flow out of control. In fact, it can roustabout so rapidly that the tube is destroyed. This is because after a gas discharge tube lights, resistance to current flow decreases; as more and more electrons are freed, current flow accrues. So like walking a tight rope, runaway current must be poised. And it is balanced by an electromechanical implementation called a magnetic shunt. The magnetic shunt is found in both the fluorescent ballast and the neon transformer core. It acts as rigging to retard current flow changes through the core. It does this just long enough so that a characteristic of the electric input stops the runaway potential.

    By alternating the input current (AC) about sixty times per second (60Hz), the changing flow helps moderate current amplitude. Between alternating the input current and resisting changes in current flow with the magnetic shunt, runaway current fiesta is wholly confined on the midway. However, the modern solid-state ballast and electronic neon transformer use special circuitry and higher alternating frequencies to regulate current flow and increase operating efficiency; computer controls effectively suppress a lot of electrical clowning around.

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    Though both neon and fluorescent lighting systems share similar electromechanical rigging, not all electrical values are the same. A standard 40-watt, four-foot fluorescent tube operates at nearly 1/2 amp of current flow. And High Output (HO) and Very High Output (VHO) fluorescent tubes respectively run about 2 to 3 times this operating current. Comparing to neon, its transformer’s primary current runs between 1/2 amp and 4 amps depending upon the transformer and its load. Neon’s secondary current is typically balanced at 20, 30 or even 60 milliamps. And while a fluorescent tube starting voltage climbs to 400 or 600 volts, it falls in at a running voltage of around 95 volts.

    By comparison, the standard neon transformer starting voltage is 1/2 to 2 times the rated operating voltage depending upon transformer load: 22,000 to 30,000 starting volts for a 15,000-volt transformer! However, newer solid-state ballast and transformer models operate with high frequency current in the thousands of cycles per second (kHz) increasing the efficiency of both lighting systems. Electronics it seems are better at the high-tension wire act.

    Skipping the whole power-factor shill, the fluorescent tube produces between 50 and 100 lumens of light per watt depending upon design. Compare this with the typical incandescent light bulb that produces between 10 and 20 lumens per watt. Neon light efficiency is based upon much fancier pants, the color of its output, which ranges from 10 lumens per watt for red to 60 lumens per watt for green or blue. One reason that green and blue tubes are more efficient is that phosphor coatings used to produce such colors better ballyhoo the high-energy ultraviolet light from the argon/mercury mix into visible colors. One reason that the fluorescent tube is more efficient than a neon tube is that a large straight tube offers less resistance to electrical current flow than a skinny bent one.

    Common fluorescent tube diameters are 1 and 1 1/2 inch. Common diameters for neon tubes run about half these figures. Of course, fluorescent tubes seldom burn as long as cold cathode neon tubes, as fluorescents have built-in life expectancy. And VHO fluorescent tubes operate at temperatures as high as 325 degrees Fahrenheit potentially shortening their life even further. But because neon is handcrafted and uses mischievously high secondary voltage, fluorescents generally win the lower maintenance award. And with their new perch replacing the incandescent light bulb, compact fluorescents will be in the spotlight for a long while indeed.

    Both neon and fluorescent tubes use low pressure, inert gas fill. And in “blue tubes,” neon and fluorescents share phosphor coatings and mercury in their toot-up act. But a fluorescent tube is usually made up of soda glass though some specialty tubes costume in borosilicate for specific venue. Although most neon tubes are made of lead glass, sometimes called carnival glass, they can share the soda glass makeup as in “exotic” or “classic” glass tubes. Now, lead glass also seals the metal external leads to the fluorescent’s internal cathode. And this is similar to neon in that lead glass seals the lead-in wires to the electrode shell. Lead glass it seems is one versatile performer.

    So you can see, neon and fluorescents are similar critters in the lighting arena. Any differences between them help fill a concession, a gig under the big top of tube lighting systems. No doubt eventually, new players will phase out each. But until that day comes we townies can appreciate the funfair that each brings to what would have been our lantern-lit, dog-and-pony sideshow lives.

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