Interesting Flourescent warmup

[imj]

Hi all, I bought a 36w Philips Super80 TLD flouro tube( those with the green caps). When first turned on , I expected it to light normally but to my surprise it din't. The area near the ends glowed much brighter than the middle part of the tube. It stayed that way flickery for half a minute or so and gradually became the same brightness, reminds me of a LPS lamp warming up. At first I thought it was because the tube was new but the next day the same thing happened and still happens now after a week! Can't be the weather cause I live in asia so the only cause could be the lower mercury dose of these new tubes which is around 3mg.

[Chris W. Millinship]

We have some Sylvania "Luxline Plus" 6 foot T8 colour-860 tubes in the office at work and in the morning when first switched on, they exhibit the same sort of behavior. This is usually most noticeable on a cold morning, probably the phosphor is cold so exaggerates the effect. Sometimes, strangely, there are two dim spots with the ends and the middle being brighter. It is probably the mercury content, I reckon it becomes unevenly distributed along the length as they cool down from the day before - the ends stay warmer for longer as they run hotter to begin with and there is more mass there retaining the heat too. As you point out, after a short while they warm up and run just fine, probably vaporises the condensed mercury back into the tube atmosphere.

Strangely, I never noticed this with the horrible "plain vanilla" 3500K colour tubes that were there originally. Perhaps those older tubes had more mercury in them. I do notice the Sylvania tubes claim to be "New Generation".

[Zelandeth]

Pretty sure Chris M is right there.  This behavior can be seen with "normal" fluorescents if they've been really well chilled (read: stuffed in a freezer to test cold starting ability...forgotten about, and rediscovered behind the bag of frozen chips a fortnight later).

Chances are that there is a fair amount of mercury condensed throughout the tube - but the heat near the electrodes will lead to it being vapourised there more rapidly - in addition to the phosphor being warmed.  This will give two reasons for that effect being seen.

This effect can quite often be seen with CFL's, though not easy to spot unless you're looking for it.

Will go chill an F8T5 and grab a couple of photos tomorrow (camera's batteries are dead just now!).

[mr_big]

I used to use these at work the only difference is that these were designed to be run on a 32 watt electronic instant stat ballast
They did the same thing for about the first 100 hours or so jsut be careful when they burn out because sometimes they go pink and stay on until the tube cracks

[imj]

Hi all/Mr big, the tube your refering to is the Philips Super80 HF 32w. The ballast that runs them, I think is dedicated by Philips like the QL lamp cause I can't find a 32w electronic ballast. Also about the pink glow, I have seen before that the normal Super80 36w tubes run on magnetic ballasts also exhibit a dim pink glow when it burns out but some do fails as normal flashing without the constant glow. I think it's the supply voltage being too high that still manages to maintain the discharge even after burnout. In my country the standard voltage is 230v but some places can go up to 245v or as low as 225v as in my house.

IMJ

[mr_big]

I use 32 watt electronic ballasts special order they don;t exist anymore we are replacing them with a different type now because of all the problems that they have been causing