Author Topic: Fluorescent black ends  (Read 1276 times)
Jan_it30
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Fluorescent black ends « on: September 01, 2022, 10:37:39 AM » Author: Jan_it30
A few years ago i Saw some fluorescent tubes with black ends caused by the use but on this days none of my preheat fluorescent tubes has a black ends. Are the newer tubes improved to aboid the filament material fall on the tube ends?
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sol
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Re: Fluorescent black ends « Reply #1 on: September 01, 2022, 01:12:01 PM » Author: sol
It depends on the lamp. Some have cathode guards which is a metal strip formed into a band around the electrode filament. It is designed to "catch" the blackening before it reaches the phosphor. However, when the lamp is close to EOL, so much material is sputtered that the guards cannot catch it all and the end blackens. Those lamps run relatively clear until EOL is close. Of course, some lamps don't have them and will gradually blacken over their life, sometimes starting fairly early and running most of their life with slightly black ends.
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Jan_it30
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Re: Fluorescent black ends « Reply #2 on: September 01, 2022, 03:04:57 PM » Author: Jan_it30
Thanks, and how i can know if my lamp has the cathode guards?
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Medved
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Re: Fluorescent black ends « Reply #3 on: September 01, 2022, 03:40:27 PM » Author: Medved
A good method to reveal the internals is shine onto the side by a laser pointer (so make the spot a kind of pointy light source) and look what the shadow looks like on the other side of the tube. Either you will se just tiny shadows of a few wires, or plate-ish shadow of a bigger object, like the cathode guard ring (usually made from a 5..10mm wide metal band strip, bended and welded into a kind of ring shape around the filament)
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Jan_it30
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Re: Fluorescent black ends « Reply #4 on: September 01, 2022, 04:25:12 PM » Author: Jan_it30
Ok i Will try, the fluorescent tubes takes more time to preheat if Its more used or the EOL event is almost instant?

And i have an other fluorescent that are a F14T5 and i can see a black dot on one end of the tube, This bulb runs on a electronic ballast with instant start. Are This dot a drop of Mercury?
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Medved
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Re: Fluorescent black ends « Reply #5 on: September 02, 2022, 12:47:01 AM » Author: Medved
Is it moving around the tube?
Some makers used rathed unorthodox way to ensure the amalgam pellet (the thing where the Hg resides) is always in the almost coldest spot of the tube: They just left it lose in the tube, so regardless of the position, it slide down, where it most likely be the coolest.

F14T5 is a lamp that uses to operate with tube wall way hotter than would corespond to the optimum Hg pressure, so the Hg reservoir amalgam pellet has to be placed away from the arc, where the tube is not that hot. Some makers make lead wires on one end longer, so the part of the tube behind the electrode is long enough to keep tge place around the seal cold even when not really at the bottom side. And some just keep the pellet free to move inside, so it slodes down, to the end tgat is the bottom one, where the cold air drawn around the tube keeps that part colde enough.
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BlitzBiker2001
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Re: Fluorescent black ends « Reply #6 on: September 12, 2022, 09:05:28 PM » Author: BlitzBiker2001
In my experience of changing tubes, pre-2005 Philips lamps in my opinion are the biggest offenders when it comes to to transfering burnt filament material to the phosphor. Sylvania lamps when they burn out just tend to only burn a small circle into the phosphor. Philips lamps do have the filament guard, and Sylvania lamps do not, so I actually think it has the opposite affect.
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