Thanks. That's quite a difference. How are BLB or BL tubes affected by voltage fluctuations? I have the non-blue ones that look like regular fluorescents.
By the way, I used 24 gauge galvanized steel
You have the regular BL tubes. They print slightly faster than the BLB tubes which are blue.
Voltage fluctuations with the BL and BLB tubes can be a considerable problem, as with cold-light enlareger heads, though the magnitude of the problem can vary a lot by locale, and by the time of day when you print.
If you are printing with gum or carbon, the fluctations can be compensated in development. With other alternative processes, I recommend an integrator. And, BTW, the Metrolux wil work with UV sources with the photo cell provided for enlargers. Although I use an Olix integrator at this time with my UV bank I used a Metrolux in the past and it worked just fine.
Originally Posted by Neil Poulsen
Neil, my humble apology, Sandy is correct!
I should have written 5,000/6,000 hours.
I use and have used tubes, which have a stable life as I've just mentioned of thousands of hours.
We have found that after about 6,000 hours, the tubes start to get hot spots, or, more correctly, cool spots. This results in uneven exposure. We run a double shift, the lamps are on approximately 17 hours a day, they last from 8 months to about 11 Months before they go off.
We have a couple of smallish units running six 2' tubes which are switched on and off during the day. These seem to last the same length of time as the continuously on tubes. All of our machines are fitted with timers which time the length of time the lamps/tubes are on, so we can monitor actual against predicted costs.
I shouldn't have written that reply before starting work, comes from having a peek just to see what has happened overnight in the other hemisphere.
The Nuarc is pretty much on the way out at after 6 months of use, which equates to just under 1,000 hours the way it's run.
Just the question, friends - why everyone wants to use BL or BLB tubes instead of real real germicide (transparent) tubes? They give MUCH sharper UV, about 254nm long, so they would print much faster (though the precautions against skin and eye burning should be much more serious)? I mean that if I were doing an UV box for printing, I would put there just a bank of germicide tubes, not the softer BL kind.
There are several reasons people do not use these type of tubes. UV radiation at the 254 nm range is extremely dangeous to human beings, and the risk is much greater than just skin and eye burns as it is known to be a cause of cancer.
And second, ordinary soda lime float glass, which most of us use in our contact printing frames, blocks a very high percentage of UV radiation below 350 nm, and virtually all of it below 300 nm, so not only is radiation at 254 nm very dangerous, it is also useless.
There are some speciality glasses, such as bososilicate, also known as fused silicate, and quartz, that transmit a very high percentage of light below 300 nm. But this glass tends to be very expensive and not easy to find.
Originally Posted by eumenius
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Ah, that's what I thought about - low transmission of short UV rays through regular glasses, and 254 nm UV is indeed too dangerous (though cancer is too much for it, one gets faster burned to bones rather to contract cancer from mercury lamps). So the longer, softer UV is way much better for a regular darkroom, of course. I just remembered the UV tables with deep-violet UV filters in them, some are more than 18*24cm - each containing ~400W worth of 254 nm bulbs... we use it in our lab to visualize and cross-link DNA molecules. Ooops, that's the trouble with human beings
Originally Posted by sanking
I think there is a bit of confusion here, just like at the start of the thread with the "anodized" aluminum...
Originally Posted by sanking
I'm guessing that "fused silicate" should actually be called "fused silica", and it is not related to borosilicate glass. Fused silica is another term for quartz glass. It is composed of relatively pure silica, SiO2, which also found in the mineral quartz.
Borosilicate glass is the type of glass that is found in Pyrex and Kimax laboratory type glassware. Borosilicate glass conatins boron in addition to silica.
Yes, borosilicate and fused silica (quartz) are different animals. My apologies for the confusion.
But regardless there is little to be gained with speciality glasses of this type, and the risk to human beings of radiation below 300 nm is significant.
Originally Posted by Kirk Keyes
Last edited by sanking; 12-09-2005 at 08:35 AM. Click to view previous post history.
UV absorbing paint pigments
Hello. I am new to the forum and scanning for information related to building UV printing light sources. This thread is very interesting.
About painting the surface behind the bulbs. If you choose to do so you should expect a portion of the light to be re-emitted with a wavelength shift. This will be a varying amount of the light as much will pass through and be reflected by the metal (thus having a second pass and chance to be absorbed and re-emitted). Paints heavy with titanium dioxide are classic UV absorbers and re-emit within the visible spectrum.
You sometimes see this effect used to reduce reflected UV into exhibit cases housing sensitive museum/gallery artifacts.
Mark MacKenzie, M.A.C.
Past Ink Publishing
Just Finished Today
I just completed my uv source today. It works great. Again, thanks for all the input.