Diffuser for UV Box

[4LivingWage]

I need some advice. I assembled a UV box using 8 Barrina leds (~390nms). The lights sit about 2 3/4 inches above the print frame and I'm getting banding. Can I place an acrylic Plexiglass Sheet, White Translucent 55% (2447), between the lights and the frame to diffuse the light? I know it will prolong print time but that isn't an issue. Thanks for any advice. BTW, I'm using it mostly for Kallitype and Cyanotype, for now.

 

[gbroadbridge]

You would be better off simply raising the light source thus letting the lights overlap.

 

[4LivingWage]

You would be better off simply raising the light source thus letting the lights overlap.

I need some advice. I assembled a UV box using 8 Barrina leds (~390nms). The lights sit about 2 3/4 inches above the print frame and I'm getting banding. Can I place an acrylic Plexiglass Sheet, White Translucent 55% (2447), between the lights and the frame to diffuse the light? I know it will prolong print time but that isn't an issue. Thanks for any advice. BTW, I'm using it mostly for Kallitype and Cyanotype, for now.

Would 8-9 inches distance from leds to print frame be sufficient or would adding the diffuser as well be best?

 

[koraks]

Can I place an acrylic Plexiglass Sheet, White Translucent 55% (2447), between the lights and the frame to diffuse the light?

You'll lose a considerable amount of light.
Also, the diffuse light will evidently be less collimated, which will affect how crisp e.g. masked edges will print, but also the microscopic detail within the image area itself. The latter may or may not be relevant to you; you'd have to try with more diffuse vs. more collimated light sources. I personally prefer a more collimated light source; i.e. a single light source at a larger distance.

 

[4LivingWage]

You'll lose a considerable amount of light.
Also, the diffuse light will evidently be less collimated, which will affect how crisp e.g. masked edges will print, but also the microscopic detail within the image area itself. The latter may or may not be relevant to you; you'd have to try with more diffuse vs. more collimated light sources. I personally prefer a more collimated light source; i.e. a single light source at a larger distance.

Thanks for your response. I will raise the lights another 6 inches and hopefully that will resolve the problem. I also was advised that the silver tape I lined my box with was not a good idea and that matte white paint would better. I'm not sure why, but I will await a response.

 

[koraks]

The silver tape vs. matte white paint won't make all that much of a difference. The LEDs are fairly directional; i.e. they beam downward. So whatever is above your LED strips/bars will only reflect light that was reflected back into the light source by the printing frame and its surroundings anyway. Theoretically you might get a little unevenness if the backing doesn't also diffuse the light, but in practice this is really a non-issue. More relevant is the spacing of the LED bars/strips; the closer you bunch them together, the less distance you need between the light source and the printing frame for even coverage.

Just increase distance until you get even coverage. It'll work, regardless. Then go with whatever printing times are needed to get the job done. If those are too long to your taste, increase power by adding bars/strips in the empty spaces or switch over to a different light source that's inherently more powerful.

 

[jeffreyg]

I do pt/pd. My light box is from Bostick and Sullivan and is painted matte white interior. I have been using black light bulbs for years. They are pretty close to the printing frame. Have you checked the spacing between the bulbs? I have never experienced banding.

 

[4LivingWage]

The silver tape vs. matte white paint won't make all that much of a difference. The LEDs are fairly directional; i.e. they beam downward. So whatever is above your LED strips/bars will only reflect light that was reflected back into the light source by the printing frame and its surroundings anyway. Theoretically you might get a little unevenness if the backing doesn't also diffuse the light, but in practice this is really a non-issue. More relevant is the spacing of the LED bars/strips; the closer you bunch them together, the less distance you need between the light source and the printing frame for even coverage.

Just increase distance until you get even coverage. It'll work, regardless. Then go with whatever printing times are needed to get the job done. If those are too long to your taste, increase power by adding bars/strips in the empty spaces or switch over to a different light source that's inherently more powerful.

Thanks again. My print times are ~1 minute for Kallitype and ~5 mins for Cyanotype classic, so even doubling won't be an issue for me. I just got started 5 months ago so I'm still in a rapid learning phase. Having fun.

 

[4LivingWage]

I do pt/pd. My light box is from Bostick and Sullivan and is painted matte white interior. I have been using black light bulbs for years. They are pretty close to the printing frame. Have you checked the spacing between the bulbs? I have never experienced banding.

Spacing is 2 inches apart. Funny, I didn't notice banding with Cyanotype, but I am now seeing it in Kallitype. I wonder if the chemistry makes it more noticeable.

 

[koraks]

Thanks again. My print times are ~1 minute for Kallitype and ~5 mins for Cyanotype classic, so even doubling won't be an issue for me. I just got started 5 months ago so I'm still in a rapid learning phase. Having fun.

Sounds good - have loads more fun!

 

[jeffreyg]

I haven’t measured how far apart the bulbs are from each other but it is less than two inches.

 

[4LivingWage]

Here's an update. I raised the lights so now they are 8 3/4 inches from the printing frame. My cyanotype prints now take ~9 minutes, almost double what they used to but no longer have any banding. I also lined the box with a matte white contact paper to cover the silver foil tape. So, I should be good to go now.

 

[koraks]

Perfect, well done!
If the exposure time bothers you, you can always try to increase the density of the lights by adding some more.