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  1. #11

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    Neal, the lamp output is more consistent if it is kept on for the duration of the printing time.

    I beleive King uses a compensating timer with his units and gets very consistent results, drop him a line and ask him.

  2. #12

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    Neil,

    The first rule of using fluorescent tubes is to turn them on and leave the on. On/off on/off on/off is not good for the tubes or the ballasts, also you use more power on start up then run time. I have done it this way for years. When I, first started printing I used a sun lamp I turned it on and left it on. During the winter months I would have exposure problems and could not work them out until I found the cat sleeping under the lamp and on top of my print frame.

    The light box is better no room for the cat.


    Jan Pietrzak

  3. #13

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    Quote Originally Posted by Jan Pietrzak
    During the winter months I would have exposure problems and could not work them out until I found the cat sleeping under the lamp and on top of my print frame.
    Did your cat come out solarized?

  4. #14

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    Neil,

    Jan is correct in that you will get more consistent results if you leave your bank of UV tubes on through a working session rather than turn them off and on for exposures in the 3-10 minute range.

    However, the difference between leaving them on and in just turning them on and off with a straight timer is not very great. Tubes, unlike HID lamps, tend to reach maximum output within just a few seconds after turning them on, and they don't begin to drop in radiation unless they get hot (over about 100F). A fan is critical for this. So for exposures over about five minutes I would just turn them on and off for exposure.

    I use my bank of UV tubes with an Olex light integator and a probe specific to BL tubes. However, in comparing results with the integrator, and a straight second timer where I just turn the unit off and on for exposure, there really is not a huge difference, and although I am pleased to have the extra degree of precision I could probably still do good work without it. However, the technology is fairly inexpensive, if purchased used on ebay, and so on the whole I would recommend the integrator.

    Bottom line is this. UV tubes, with appropriate ballast, provide a very consistent and reliable source of radiation in the 5+ minute range, even if you just expose with an off/on timer. But this depends on having a fan on the unit to keep the tubes cool. For most precision and consistent results, especially with processes such as Pt./Pd. where you do not have as much control of final density as you do with gum and carbon, the integrator is very useful.

    Sandy

    Quote Originally Posted by Neil Poulsen
    I thought it was alumuminum, but could be mistaken.

    To Jan:

    I'm curious about your recommendation to keep the lights on all the time. Why should I do this? At Photographers' Forumulary, where I took Dan B's workshop on pt/pd and digital negatives, they had the units connected to a Gralab 300. I suspect your recommendation is to maintain better consistency, but thought that I would ask.

    To All:

    Has anyone tried using a compensating timer, either the now discontinued Zone VI or the Metrolux with UV sources? I'm wondering if that would help consistency? Do the sensors respond to UV light in the same predictable way that they respond to the fluorescent tubes used in cold light heads?

    Probably the best is a single, high output, UV tube that's integrated over time.

    Is the inconsistency going to be that bad, is it really an issue? Six minutes exposure to UV light is not subtle.
    Last edited by sanking; 12-05-2005 at 09:38 PM. Click to view previous post history.

  5. #15
    marko_trebusak's Avatar
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    I think that you heard a lot of voices, that says reflector doesn't matter. I don't use any metal behind tubes, and I don't see any unevenness on prints. As far as "galvanization" versus "anodization", let say that anodization is one of galvanic processes. So it's correct either way, but anodization is more precise term .

    Marko

  6. #16

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    Thanks.

    I appreciate everyone's response. I'm checking with Metrolux to see if their compensating timer photo cells can tolerate U.V. reliably. (I have the Zone VI timer, but Calumet no longer has the photo cells.)

    I installed three 4.5 inch fans with plenty of large holes on the opposite side for good air volume. The fans are split 50/50 for the UV tubes below and for the ballasts and starters above. With the input that I've received, I think that I'll install a separate circuit for the fans, so that they're going all the time. That should do a pretty good job of keeping things cool. (Hopefully.)

    Again, thanks.

  7. #17

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    Neil,

    All the boxes I have built have used pegg board on the tops to vent the heat.
    The next part was to make drying screens the same size as the boxes and stack them with spacers to dry my prints. Dry time about a 1/2 an hour.

    Jan Pietrzak

  8. #18
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    I've been using UV exposure units for over 30 years in the graphic arts and rubber stamp industries.

    The main requirement of any of these exposure units is to ensure that as the lights lose their power/intensity you can work out how much extra time is required to give the same amount of light per exposure.

    As for turning them on and off, well the super expensive units designed for extremely exacting work, all run their lights continuously using a shutter blind for exposure. These machines almost always come with a small exposure receptor which measures the energy/light being given and shut the blind when the correct level has been reached.

    All smaller/normal units just work on a timer to turn the lights off. One has to compensate manually to the ageing light globes giving a lower light output.

    I myself have built a couple of UV units for exposing graphic materials like film and for manufacturing negatives and manufacturing stamps using liquid or sheet polymer. All of these units just use a timer and the lights go on and off all day every day. Trust me when I say they never seem to be effected by being turned off and on constantly.

    All units I have seen, only use a polished reflector above the UV tubes themselves.

    I take a light reading using my Gosson Profisix meter when the tubes have been run in, which is about 3 hours of use. Once a week I take a reading with the meter to find out just how different the lamps are. Basically the lamps drop off in the first month then become very stable for the next 500/600 hours of use. They then start to drop off quickly and times have to be extended to compensate too much so they are replaced.

    Taking a light reading of your old tubes before you replace with new ones also gives you a reference for starting times with the new tubes.

    Mick.

  9. #19

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    Based on Mick's input, I'm wondering about a regimen of preconditioning new bulbs by leaving them on (in a separate unit) for the time it takes them to become consistent. I could rotate them through the exposure unit, say one lamp every 24 hours or so, and maintain that process. Connecting a clock to the exposure unit would keep track of service time.

    When a bulb goes out and is replaced with a new bulb, I'd end up with an ueven light source. The above process would maintain a fairly consistent and even light source. Given that I have 15 lights placed side-by-side, each bulb would be in service for about 400 hours, assuming a 52 hour break-in period. That stays well within the phase of consistent lighting to which Mick refers.

    I'm also wondering about a shelf between the lights and the printing frame that could be easily removed. I could turn on the lights and allow a 30 second warmup period before removing the shelf. The lights would go out when the timer stops. The Gralab 300 timer makes this easy. That wouldn't be quite as good as shutters, but perhaps better than just turning them on.

  10. #20

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    I suspect that Mick's comments are based on the use of HID bulbs, not tubes. If what he wrote was meant to apply to tubes I would have to disagree because in my experience BL and BLB tubes do not begin to show any reduction in output at 500 hours. The tubes are rated for thousands and thousands of hours, up to about 18,000-20,000 thousand as I recall, and at 500 hours they are still relatively new. I used a UV bank of BL tubes for over five years without ever changing any of the tubes and did not observe any decreae in output over that period of time. I did not keep tabs on total hours of use but I suspect that it was in the 3,000 + range, if not higher.

    On the other hand, the HID buls in platemaker like the Nuarc and Olex have a much shorter life, and I would not be at all surprised that at 500 hours their output has dropped considerably.

    In any event the use of an integrator provides consisenty in exposure, even if the output of the lights were to drop,

    Sandy


    Quote Originally Posted by Neil Poulsen
    Based on Mick's input, I'm wondering about a regimen of preconditioning new bulbs by leaving them on (in a separate unit) for the time it takes them to become consistent. I could rotate them through the exposure unit, say one lamp every 24 hours or so, and maintain that process. Connecting a clock to the exposure unit would keep track of service time.

    When a bulb goes out and is replaced with a new bulb, I'd end up with an ueven light source. The above process would maintain a fairly consistent and even light source. Given that I have 15 lights placed side-by-side, each bulb would be in service for about 400 hours, assuming a 52 hour break-in period. That stays well within the phase of consistent lighting to which Mick refers.

    I'm also wondering about a shelf between the lights and the printing frame that could be easily removed. I could turn on the lights and allow a 30 second warmup period before removing the shelf. The lights would go out when the timer stops. The Gralab 300 timer makes this easy. That wouldn't be quite as good as shutters, but perhaps better than just turning them on.

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