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Dying fluorescent lamp flashes

Hello, all. I have an old compact fluorescent lamp that has served admirably for many years. I finally had to take it out of service because it started flashing. The lamp is the old non-electronic ballast type. The ballast appears to be nothing more than a big inductor in series with the tube. The lamp lights OK at first, then after several seconds (maybe as much as 30) it starts flashing: The tube goes dark, then the heaters on the ends glow, there is a blue flash visible from the end where there is no phosphor, the lamp lights... and a second or two later the whole thing repeats.

So, any idea what causes this? When the tube is lit, it appears to be about normal, or maybe with a bit of extra flicker. My best guess is that "something" has changed in the gas, either leaked out or plated out on a surface, etc, such that it will only conduct properly when warm. So it starts OK, but after the heaters cool down it can no longer support the discharge. But what exactly is that "something" that has changed?

Thanks!

So Bob Masta dqatechATdaqartaDOTcom D A Q A R T A Data AcQuisition And Real-Time Analysis

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Reply to
Bob Masta
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The heaters (filaments, electrodes) do not support an arc as well as they used to.

The filaments are coated with a thermionically emissive material. Usage causes wear and starting also causes wear on this material. It chemically degrades, evapotates, and/or sputters (molecules of the material get dislodged by positive ions crashing against the negative electrode).

You reach a point when there is so little left that you need extra heat to get it to sustain the arc.

Often in fluorescent lamps, the arc does some working from the filament material itself in addition to or instead of the thermionic coating before the lamp completely dies. When that happens, some filament material usually sputters and noticeably blackens the end of the tubing where that happened.

- Don Klipstein ( snipped-for-privacy@misty.com)

Reply to
Don Klipstein

Bob Masta submitted this idea :

try replacing the starter. thats a small metal can with 2 terminals on it.. it removes with a slight twist and pull action. They're cheap. look at the ends of the tupe. Are they dull or going black? bad tube.

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Reply to
Lawrence Oravetz

Electron-emitting material on the heaters has worn out from use and/or from cold starts. This is a normal inevitable failure mode of hot-cathode fluorescent lamps in general, as well as at least most high pressure mercury vapor lamps and sodium vapor lamps of either high or low pressure.

The heaters are normally kept hot enough to thermionically emit electrons at an adequate rate by heating from the ends of the arc in the tube. This fails when the thermionically emissive coating is worn away.

- Don Klipstein ( snipped-for-privacy@misty.com)

Reply to
Don Klipstein

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