|MadSci Network: Engineering|
Hello Sterling: The fluorescent lamps you refer to are probably a mix of mercury and argon gas. There are many ways that lead to failure because of interaction between the ionizing electrodes and types of ballast. Here are some pointers for troubleshooting: Bad fluorescent tubes: Unlike incandescent lamps where a visual examination of the bulb itself will often identify a broken filament, there is often no way of just looking at a fluorescent tube to determine if it is bad. It may look perfectly ok though burned out fluorescent will often have one or both ends blackened. However, a blackened end is not in itself always an indication of a bad tube. Blackened ends are a somewhat reliable means of identifying bad tubes in 34 or 40-watt rapid start fixtures. Blackened ends are not as reliable an indicator in preheat or trigger start fixtures, or for tubes of 20 watts or less. Failure of the electrodes/filaments at one or both ends of the fluorescent tube will usually result in either a low intensity glow or flickering behavior or sometimes in no light at all. A broken filament in a fluorescent tube used in a preheat type fixture (with a starter) will usually result in a totally dead lamp as there will be no power to the starter. Dim glow is rare in this case and would probably be confined to the region of the broken filament if it occurs. The best approach is to simply try replacing any suspect tubes - preferably both in a pair that are driven from a single ballast. In fixtures where rapid start ballast runs two tubes, both tubes will go out when one fails. Sometimes one or both tubes will glow dimly and/or flicker. If one tube glows dimly and the other is completely dead, this does not indicate which tube has failed. The brighter tube may be the good one or the bad one. The bad tube usually has noticeable blackening at one end. It may pay to replace both tubes, especially if significant labor costs are involved. In addition, prolonged dim glowing may degrade the tube that did not initially fail. In trigger start fixtures that uses one ballast to power two 20-watt tubes, sometimes both tubes will blink or intermittently dim. Replacing either tube with a known good tube may fail to fix this. The tubes may continue blinking or intermittently dimming until both are replaced with brand new tubes. This sometimes indicates borderline low line voltage ("brownout," etc.), non- ideal temperatures, or a borderline (probably cheaply designed) ballast. Bad starter (preheat fixtures only): Faulty fluorescent tubes continuously trying to start unsuccessfully may damage the little starter. It is a good idea to replace the starter whenever tubes are replaced in these types of fixtures. One way that starters go bad is to "get stuck". Symptoms of this are the ends of the affected tube glowing, usually with an orange color of some sort or another but sometimes with a color closer to the tube's normal color if arcs form across the filaments. Occasionally, only one end arcs and glows brightly, and the other end glows dimmer with a more orange color. Note that this is hard on both the tube and the ballast, and the defective starter should be immediately removed. Should one or both ends glow with a bright yellowish orange color with no sign of any arc discharge surrounding each filament, then the emissive material on the filaments is probably depleted or defective. In such a case, the tube should be replaced regardless of what else is wrong. If both ends glow dim orange colors, then the filaments' emissive coating may or may not be in good shape. It takes approx. 10 volts to form an arc across a healthy fluorescent lamp filament. Defective iron ballast: The ballast may be obviously burned and smelly, overheated, or have a loud hum or buzz. Eventually, a thermal protector built into ballasts will open due to the overheating (though this will probably reset when it cools down). The fixture may appear to be dead. Bad ballast could conceivably damage other parts as well and blow the fluorescent tubes. If the high voltage windings of rapid start or trigger start ballasts are open or shorted, then the lamp will not start. Ballasts for fixtures less than 30 watts usually do not have thermal protection and in rare cases catch fire if they overheat. Defective fixtures should not be left operating. Bad sockets: These can be damaged through forceful installation or removal of a fluorescent tube. With some ballasts (instant start, for example), a switch contact in the socket prevents generation of the starting voltage if there is no tube in place. This minimizes the possibility of shock while changing tubes but can also be an additional spot for a faulty connection. Lack of ground: For fluorescent fixtures using rapid start or instant start ballasts, it is often necessary for the metal reflector to be connected to the electrical system's safety ground. If this is not done, starting may be erratic or may require you to run your hand over the tube to get it to light. In addition, of course, it is an important safety requirement. Also look-up on the Internet: www.britannica.com/eb/article?eu=119363&tocid=68943#68943.toc www.misty.com/people/don/f-lamp.html www.misty.com/people/don/dschtech.html Your MAD.SCI Micro.
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