Do Flash Tubes Go Bad?

[JoeKitchen]

A former assistant of mine just bought some really old Comets, like 20+ years old.  He reached out to me because the color is not consistent between the heads and feels that the flash tubes have gone bad.  He wanted to know if he could gel them to try and match color. 

I told him that I really don't think flash tubes go bad, especially if they are well made, and more then likely the capacitors in the packs are wearing out. 

My thought on flash tubes is that they are filled with noble gasses that are not going to change chemically.  Also, since the metal cathodes are in a noble environment, they are not going to corrode.  The cathodes are thicker and I presume made of a material less brittle then a tungsten filament, so breaking is kind of out of the question too. 

I kind of feel they are like neon lights, they just continue to work until the glass cracks or the filament breaks loose from the cathode some how. 

Am I right here? 

[UlfKrentz]

Not familiar with this brand, but if they are very old it is very likely they just have different coatings. There have been "gold" coated tubes for portrait studios vs. "cold" uncoated for product photography. Also different glass type pyrex vs quartz glass was used and has influence on color output (while quartz glass is transparent for UV, pyrex cuts a lot of the UV light) Those old units that had a dial for intensity also have a noticeable difference between low and high-power setting (those that had firm settings through a switch like full, half and quarter usually don´t). You are right about aging of the tubes, they keep their color quite constant over their entire lifespan. They start to emit less power because the glass darkens and begin to fail from time to time at their end of life due to abrasion of the electrodes. Of course any mechanical damage will instantly prevent them from working, this may also be a nearly invisible small crack. Capacitors don´t have much influence on color, they just store less energy and / or have a higher leakage current which can cause other serious problems. So the cause of the different colors is probably in the optical path (either the tubes or reflectors / light modifiers)

Cheers,

Ulf

[Kirk_C]

No, Comet flashtubes don't go bad or shift in color due to age. But they did produce some flashtubes with UV coating and some without back then and that's most likely the source of a color inconsistency. They also produced different domes covering the flashtubes that were coated to adjust color temp.. That's another one of the inventions of Balcar, they offered interchangeable pyrex domes you could switch to change color temps.

I have 6 CX series Comet heads that are that old and a couple of their compact open tube heads. I just tested them with a Minolta color meter and they're 5400K +/- 100 K over the range of the packs 2400WS output. My Profoto Pro 7 heads and packs vary that much while the Profoto D1s only vary about 70K.

Dynalite and Comet merged a few years ago and all the Dyna heads since then, including the new Baja Monoblocks use the same Comet tube/head design.

[Garry Sarre]

My 25 year old floor pack was down to only one working channel, so I bit the bullet and went to see what was available. I did buy a new Elinchrom unit but I also came away with a floor pack and a couple of heads that were 30 years old. One of the tubes is quite smoky coloured, I'd be losing a stop from it. It also has a blue cast.

I discovered that with the head-shots I do, using the blue-smoky tube as a fill, gives a subtle blue sky reflection in the eyes and shadows which is to me, quite appealing.

So there you go.

[MichaelEzra]

Hi Joe, I use multiple Speedotron monolights for about 20 years and they seem to work as new. They still look like new, there is no darkening of the glass not color change. However, it is sibjective as I cannor run an exact comparison against new. Through years of use, most of the exposures were near full power, at least 1/2.

[Kirk_C]

...They still look like new, there is no darkening of the glass not color change. However, it is sibjective as I cannor run an exact comparison against new. Through years of use, most of the exposures were near full power, at least 1/2.

Discoloration of a flash tube comes from minute impurities in the Xenon gas oxidizing over time. The best flashtubes don't exhibit this discoloration. Yellowed flashtubes are typically a sign of environmental contamination where the flash was used. Cigarette smoke being the most common.

The thing that's likely changed with your Speedos is the power output unless you've had them re-capped. The dielectric in the caps dries out with age and becomes less capable of holding a charge.

[MichaelEzra]

Could be, but the loud "pop" feels the same:)) The 1000w/s Force 10 Speedtrons are insanely powerful, still - they have a longer flash duration, so the amount of light they give out is much higher than others rated at similar w/s specs. Too bad they discontinued them. I haven't measured their changes in the output, as with digital I seem to need less and less power overall (I used to shoot at 25-50 ISO on film).

[BobShaw]

I have a very old Elinchrom head that is quite dark and the flash has a definite blue cast as someone previously mentioned. It still works and I just use for a backlight now.