Hello,

New to the forum, love the site.
I have a question to ask. I had a tropic sun t832 go bad the other day. I checked it with a meter and found one of the filaments to be burned out. My question is, could I use this bulb on an instant start ballast? From what I have read, instant start does not use the filament to start the bulb.

Thanks,

Static

Actually instant start does use the filaments, or whatever it can find, you could, but it wouldn't last long!

The coiled "filament" of the electrodes in every fluorescent lamp (regardless of whether it is a T12, T8, T5, T2, etc...) is coated with what is called "emitter" material, which aids in the arc being struck in the lamp when first switched on (and also aids somewhat in maintaining the arc in a lit tube.) As the lamp ages, miniscule portions of the emitter wears off and creates a deposit which is seen as a dark band encircling the electrode ends of the tube. As the bands become darker, it is indicative of how advanced in aging the lamp has become, until eventually, the emitter completely wears off, resulting in EOL (end-of-life).  Therefore, a lamp with a broken filament will most likely fail immediately if powered on, as there would be neither emissive material (nor filament to excite it) present on one pole of the lamp. I hope this more factually answers your question.

By the way, Static, welcome to the Lighting-Gallery.net! 

It could be possible, but like Rudy (Mr. Big) said , it wouldn't last long. Here's what I think:

As Brian said (I was about saying it), fluorescents run with "hot cathodes" and these cathodes need to be coated of emissive material. I'd add that the problem is that only the filaments are coated of emissive material, not the leads that support them. As the leads have a lower resistance than the filaments, if they (filaments) are broken, the current will follow the easiest path, a.k.a. the leads. Without emissive material, they (leads) will run extremly hot and will most likely melt. Then the melting lead will unseal the stem and the lamp will lose its vacuum.

I have myself run some fluorescents with a broken cathode on a trigger start ballast. The cathode overheats and the lamp looses its vacuum.

If you need more details or if you don't understand, let me know!  

Actually, Vince, you are 100% right...in fact, you sort of pointed something out that I have always wondered, which is why T8s always lose vacuum and never rectify when they fail...    See, we all learn from each other!!! 

Thanks, I actually say what I've seen with failing lamps. I have a brand new F20T12/KB (with broken electrode) that in a few minutes began to sputter. One of the leads was very hot, so the current was most likely passing throught it, and not by the filament. I have another tube, an F14T12/D. Its weakest electrode began to seiously overheat 2 min. atfer it broke (I saw the lead melt throught the phosphor). So here again the same phenomenon happened.

Oh last thing, some T8s actually rectify. It depends of the EOL. There's many scenarios possible: no emitter left, breaking electrode, mercury starving, they all produce differents phenomenons. It also depends of the ballasts.

Well, that's what I think, I'm not really an expert 

How about breaking the tube? 

It also seems like this a specialty tube

How about breaking the tube? 

In this case the lamps immediatly shuts off and the electrodes are destroyed in a few seconds  AND you receive glass pieces, mercury (if not an ALTO lamp) etc.

Wow, I did not expect such a quick answer to my question. Thanks everyone.
In the past, I use to work on old tube televisions, so I understand the that the filament is really acting as a cathode, I did not know that it was needed one the tube was started. I was looking on ebay today and almost bought a instant start ballast but thankfully I waited to post this question.

The tropic sun bulb is a 5500k bulb I use for my fish tanks. They run about $12. I found some 5000k Altos at the big orange box for 2 for $7 and gave them a try. I figured for the price it was worth it. So far they are working out. I have not noticed the difference.

Thanks again for all the information.

Static

You may notice the difference soon, as the lamp starts to go mercury starved, Philips Altos are known to be bad around here!

Another little thing static1701, yes the electrodes are needed to start the lamp, but they don't necessarly need to be intact. In theory, the fluorescent CAN run with broken electrodes on an instant start ballast, but it'll actually do what I've said in my precedent posts.

TiCoune66 - Too bad it works that way, if it would not melt it would be a good way to get a little extra life out of the bulb.

Mr. Big - Around here, I have a choice of the Phillips, Sylvania, or GE and all of them are low mercury. It is hard to find anything else.

Static

The Sylvania and GE tubes would probably be better, if the Philips go mercury starved.

Another problem with aquarium light might be with light output: Some animal species do need some mild UV content (both "A" and "B") in the light (UV is antiseptic, to avoid some skin diseases buildup - it hose bulbs it is to emulate it's natural sunlight content present in the original ecosystem), that's what makes difference between "terrarium" (strong A, weak B), "aquarium" (significant A) and "cool daylight" (no UV - intended for general lighting) lamps, even if all have same apparent color temperature.
So be careful to not put the wrong light for species you have there...

I found a deal on a instant start ballast on eBay. I got it the other day and tried the bad bulb and it fired up. the bad end was glowing yellow and it had a few swirls. I turned it on and off a few times and the last time it lit up but did not have the yellow glow. I wonder if it will stay working for awhile. I also I have a black light bulb that is dead (both ends) and it works fine on the instant start ballast. As soon as I get some time to mess with it again, I will try leaving them on and see if they melt the glass.

As far as the fish, I have plastic plants in the fresh water tanks and just fish in the salt tanks. I do run 50/50 bulbs on the salt tanks.

Static