Re: Slightly OT: What makes flouescent bulbs fail?

A lot of failures for flourescent bulbs are caused by voltage fluctutions such as those cause by turning on and off a piece of woodworking equipment. It causes the mercury vapor in the bulb to plate out on the glass. The reason you see the dark regions at the ends of the bulbs after a while is the aforementioned plating. This is a another very good reason to have your lighting circuit on a different circuit than your power tools. It will minimize the voltage spikes as you are adding and subtracting loads from the system and make your bulbs last longer. Welding machines will REALLY give flourescents hell. I installled a 100A sub panel in my Garage/Shop specifically for my equipment loads. I left the lighting circuits feeding from my original house lighting panel which has a 3/0 200A service. I get very little flicker in my lighting. Lucky for me I was able to use "spare parts" from my job as an Electrician and saved a significant amount of money on installation.

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wrote:

Sometimes I find that it is a matter of removing and re-seating the bulbs. Sometimes the sockets just get loose so that I cannot get a good connection -- one fixture I had always required reaching up and twisting/jiggling one of the two bulbs in a 4' fixture. Two, 2-bulb 4' fixtures recessed between joists I have in my kitchen -- the main light fixtures -- have had the same bulbs for 15 years, no problem. Go figga'.
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"It varies". the house I grew up in had strings of flourscents in fake beams for lighting the living room. we never had to replace a bulb in 20+ years. OTOH, a room dedicated as an 'office', went through at least 3 complete replacements of bulbs in _every_ fixture in that selfsame 20 years. We also had half-a-dozen open fixtures in the basement, and may have replaced all those bulbs _once_ each in 25 years. These were the old types with the separate 'starter' thingie. We went through more starters than bulbs.
Note: *same* bulbs used throughout the house. we purchased several cases as a single buy from a commercial supply house. When we replaced a bulb, we were replacing with an 'unused' one of the _same_vintage_ as the one that died.
The design of 'two tube' (or 'four tube') floursecents is such that the bulbs operate in 'pairs'. If one bulb fails, the other _will_ quit operating.
Flourscents nearing the end of their useful life _do_ get "finicky" about a lot of things. Minor variations, _dips_, in the electric supply _will_ cause them to 'turn off'. And, of course, the 'starter' circuit doesn't kick back in. Simply switching the fixture off, waiting 30 seconds or so, and switching it back on will often cause the bulbs to re-fire.
Comment: you'll find a _much_ better grade of bulb at a commercial lighting distributer. Minimum purchase is usually a case of 12, at least in the 4' size. Case price, vs single bulbs at retail outlets, is attractive, too..
Personal experience has shown that 'major brand' bulbs _do_ have a significantly better life expectancy than the no-name ones. I havn't had need to go shopping for probably 15 years, but, back then, GE made the 'good' ones, Sylvania was a ways back, in 2nd place, and everybody else was "also rans", back at the horizon.
I see that (at least some) GE 'small' flourscents , like for 24" fixtures, are now imported from China. I suspect that durability has suffered.
As for what makes the bulbs fail, barring 'catastrophic' things like breaking, the bulb ceases working, when it can't make an 'arc' from one end of the bulb to the other. THAT occurs for any of several reasons, most of which cause changes in the gaseous content inside the tube, which result in a reduction in the abilit of the medium to sustain that arc. The 'electrodes' at the end of the tube are 'hot' (temperature). The material of the electodes actually 'boils off' into the tube. That's where the 'black band' you see at the 'electron source' end of a 'used up' tube comes from.
If the 'sealing' of the tube isn't *absolutely*perfect*, you get gas migration either into or out of the tube, or both.
Note: for a tube that's failing to start, waving a VHF (or UHF) walkie-talkie close to the tube, whill keying transmit will *often* cause the tube to re-fire. The RF energy is enough to trigger the ionization that allows the ark to reach the length of the tube.
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Robert Bonomi wrote:

I used to swear by GE lamps. Now I swear at them. My recent experience with their Chinese junk is that it is junk.
Phil

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I used to make neon as a hobby. When using solid state transformers to light the tubes the mercury would migrate to one end of the tubing after a while. While flouescent fixture arent solid state I wonder if reversing the tubes end to end occasionaly would extend their life? Just wondering. Mike in Arkansas
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You mean to tell me that you've got _that_ issue of the "Journal of Irreproducable Results" at hand?
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(Robert Bonomi) wrote:

remember it only dimly. Nyuk, nyuk.
-- Regards, Doug Miller (alphageek-at-milmac-dot-com)
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