Building a UV light source

[Leonard Metcalf]

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

[Louie Powell]

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.

[Jim Noel]

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.

[Leonard Metcalf]

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

[Matt Miller]

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.

[Amedeus]

Aluminum film is a great reflector for UV ... silver and white paint not so much.

[Leonard Metcalf]

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 Metcalf]

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 Metcalf]

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

[Eric Woodbury]

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.