What would cause a 8' HO fl. tube to be bright at the ends, but dim in the centre of the lamp? The installation in question is an outdoor sign. The sign ballast and 4 tubes are brand new. The 3 tubes light strongly, but the 4th is as described above. My best guess is either the cold weather, or the socket isn't making a solid connection?

[This message has been edited by Sandro (edited 12-21-2003).]

If you switch tubes around, does the problem follow the tube, or stay with the socket?

Could be a problem with extreme cold, if the suspect tube has a lower amount of mercury fill or something.

Did someone change a ballast?? and not use a sign ballast, which are rated at -20 degrees F. A regular ballast won't work outdoors(at least where its cold) as they are rated at 50 degrees.

this sounds like a filling/temperature problem. These tubes need more voltage as colder it gets. If it's improperly filled, it also needs more voltage.
The dark area in the middle should brighten up during longer running time, does it?

NJwirenut : I did not switch the tubes around, I wish I did to check it though.

Walrus : I personally installed a proper sign ballast and new tubes. The previous maintenance guy had installed regular HO ballast.

Andy : I thought this too, don't the tubes generally get brighter as they run longer? I didn't have the time to stick around. Just long enough to see the sign fully lit, and the tubes and ballast were in my truck for several days in subzero temps. Curiously the socket on this lamp had the one side of the contact slightly indented but still made contact. I was wondering if maybe full contact was not made? The voltage concept is interesting too, the sign is approx 60' from the building and run with #14 wire. Could voltage drop be the problem? Mind you the other 3 lamps lit fully.

sorry, i dont really look through - are we talking about high voltage fluorescent lighting? or about standard fluorescent tubes?

if High voltage: Do very careful work at their connections. Loose connection can still make the tube work, even if there is for example a milimeter distance between wire and terminal, depending on the voltage the tube could still ignite and work, but with an arc burning at the loose connection!

I have some HV tubing light up our terace, when i havent run it for a longer time or/and its cold outside, some tubes show this scenario. I believe that something happens with the mercury / merc vapor, so when longer running the merc gets vaporized again what makes the light brighter.


if talking about standard fluo tubes: I've seen the dark-in-the-middle problem when running new, cold tubes on Electronic ballasts. Conventional coil ballasts should only make the tube flicker a bit and brighten up delayed when its cold.