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Thread: Building a UV light source

  1. #1
    Leonard Metcalf's Avatar
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    Building a UV light source

    I am building a UV light source for alternative processes and I was wondering what the recommended distance between the uv tubes and the contact print frame should be. I have read that 6 inches is about right, though one set of plans had a much shorter distance. Any advice on building one of these light boxes would be welcome. I have scoured the web, and haven't really come up with any clear plans.

    Thanks,

    Len

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  2. #2
    Louie Powell's Avatar
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    Re: Building a UV light source

    The problem is that if the distance is too small, light intensity will vary noticeably across the print frame. Increasing the distance solves this problem, but at the cost of longer printing times.

    I read somewhere that a good distance is equal to the center to center separation between lamps. I know that when I built my unit (using spiral black light lamps), I designed with 6" center to center spacing between bulbs, and 6 inches from the tip of the bulbs to the surface of the print frame. I can't detect any unevenness in exposure due to uneven lighting.

  3. #3
    Leonard Metcalf's Avatar
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    Re: Building a UV light source

    Oh... I have just gotten enough so I can space the tubes about a half inch apart. I was going for ten or 12 bulbs... I have laid out 8 on the table and they look like enough for the 10 x 14 inches I need. I think your right with the six inches, as some suggest 8 inch for the whole box.

    Thanks

    Leonard Murray Metcalf BA Dip Ed MEd

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  4. #4

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    Re: Building a UV light source

    In this article Sandy King says: "If you choose the two-tube holders the tubes will be separated by about 3/4 whereas the use of the individual Bipin holders and external ballast allows one to space the tubes as close together as 1/4. Close spacing of the tubes allows you to use the tubes at about 2 from the exposing plane and still get even lighting. UV banks built with two-tube holders typically have a tube spacing of around 3/4 and should be used at about 4 from the exposing plane for even illumination. In theory the closer spacing, and use of the tubes at a closer distance to the exposing plane, should result in faster printing times. However, in practice the actual difference in printing speed between units with 1/4 and 3/4 spacing is small when used at distances of between 2-4 from the exposing plane."

    A few years ago Edwards Engineering had do it yourself plans on their site. I don't see them now, but they still might be hidden there somewhere.

  5. #5
    Leonard Metcalf's Avatar
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    Re: Building a UV light source

    I am using the two tube holders because they were cheaper per bulb. Ah.. thanks I knew I had read different heights. I think I will make it with a sliding draw that I can change the height in if i need too...

    Thanks

    Leonard Murray Metcalf BA Dip Ed MEd

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    Re: Building a UV light source

    Quote Originally Posted by Louie Powell View Post
    The problem is that if the distance is too small, light intensity will vary noticeably across the print frame. Increasing the distance solves this problem, but at the cost of longer printing times.

    I read somewhere that a good distance is equal to the center to center separation between lamps. I know that when I built my unit (using spiral black light lamps), I designed with 6" center to center spacing between bulbs, and 6 inches from the tip of the bulbs to the surface of the print frame. I can't detect any unevenness in exposure due to uneven lighting.
    IN one of the final issues of The Journal of Post Factory Photography Judy Siegel describes a test in which she blacked out every other tube in her light box, laid the sensitized paper directly on the tubes and saw no banding.

    Keeping this in mind when I built my latest Fluorescent UV box, I placed the tubes as close together as possible, about 1/4", and built the box so that the surface of the print frame is 1" from the face of the tubes. NO banding is evident and print times are greatly reduced over the 6" spacing many use.

  7. #7
    Leonard Metcalf's Avatar
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    Re: Building a UV light source

    I wonder where the banding issue comes from then? I also imagine it depends on which photographic process you are using and which bulbs.

    Leonard Murray Metcalf BA Dip Ed MEd

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  8. #8
    Leonard Metcalf's Avatar
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    Re: Building a UV light source

    These comments also lead me to wonder about how critical the spacing between bulbs is.

    Leonard Murray Metcalf BA Dip Ed MEd

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  9. #9
    Eric Woodbury
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    Re: Building a UV light source

    Len

    the uneveness is the variation in distance from the tube surface to the paper. Draw it in sideview. If you have large diameter tubes, then the top of the tube is closer to the surface that at the 90 degree points. As the standoff distance increases, the variation reduces, but as you pointed out, so does the intensity. Make everything inside the box reflective, either with silver paint of a diffusive aluminum surface. Also, different diffusors such as plexiglass or flash opal glass, diffuse light better or worse and absorb different amounts, too.

    If I were you, I'd assemble the lights and find some different diffusor materials and try them at different distances. One last thing, keep in mind the light source heat. Make sure the tubes don't get too hot.
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  10. #10

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    Re: Building a UV light source

    Quote Originally Posted by Eric Woodbury View Post
    Len

    Also, different diffusers such as plexiglass or flash opal glass, diffuse light better or worse and absorb different amounts, too.

    If I were you, I'd assemble the lights and find some different diffuser materials and try them at different distances. One last thing, keep in mind the light source heat. Make sure the tubes don't get too hot.

    I would avoid any diffusion material as they are entirely superfluous if one is using BL or BLB tubes and will in all likely hood reduce the output of the exposure unit. Rather than using a reflective aluminum coating, I would recommend a very hi albedo flat white paint.

    Tubes spaced less than half the tube diameter (or less) will produce very even illumination but even if there was even wider spacing I suspect the illumination will still be even. In short I think that the fear of striping on the print is unfounded and may well fall into the realm of urban myth. I would strive for a height of 1.5 to 3 inches and possible make allowances for utilizing a vacuum easel instead of traditional spring loaded contact printing frames.

    Last, I would definitely go with 40 watt tubes as these have proven to print very fast for me.

    Good luck,

    Don Bryant

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