Anyone using LED lights for contact printing?

Discussion in 'Digital Negatives' started by John Dean, Apr 2, 2017.

  1. John Dean

    John Dean Member

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    Hello, I am going to be building a contact printing box to expose OHP negatives for Platinum/Palladium and Gum printing, as well as some silver contact printing.

    Is anyone using LED lights in such a lightbox and if so can you comment on how the compare to uv fluorecet in regard to fluorescents in terms of exposure time. Also since there are so many types of led lights on the market, which work best for this sort of application?

    Any help would be appreciated.

    John
     
  2. Brindaloo

    Brindaloo Member

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    Hi John, it's been a while since you asked your question, but I'll take a whack at it, as I'm currently experimenting with building my own exposure units based on UV LEDs.

    My first exposure unit was a massive 2'X4' fluorescent tube construction that used 10x T12 40-Watt black light bulbs. (I believe they were GE 10526.) I found that, at a distance of about five inches, my standard printing time for full exposure of cyanotypes was around 45 minutes. This was with digital negatives printed on Pictorico OHP, the "original" cyanotype chemistry, and 3/32"-thick glass for my contact printing frame.

    Last year, I moved to NYC and couldn't take my fluorescent monstrosity with me, so I decided to build a much smaller unit based around UV LEDs. Lots of people have used cheap LED strip lighting from Amazon to build exposure units, so I tried the same. A 16ft length of "3528 SMD" blacklight LEDs cost me something like $20. They claimed to emit in the 395nm-405nm range. I made sure to buy a non-waterproof version, which came free of any silicone encasing. (I figured that the silicone encapsulant, though clear, would absorb a lot of the UV light, reducing the effectiveness of the unit. I also thought the encapsulant might yellow or become brittle with age.) I cut the long LED string into shorter strings, soldered wires to them, connected them in parallel, and attached them to an aluminum plate roughly 8"x10". The resulting array was quite dense. I only conducted a few tests with the finished unit, but found that my printing times had reduced to about 20 minutes. I think the key here (compared to my fluorescent unit) is that I was able to bring my prints much closer to the UV source. I designed my wooden box so that my prints were about 1" away from the LED grid. It was not possible to bring my prints this close to the UV source in my fluorescent unit--the light fixtures I used left big gaps between bulbs.

    In the end, despite the shorter printing time, I wasn't satisfied with my strip-lighting LED approach. My construction was a bit crude, and my LEDs never seemed to illuminate evenly. (Just by looking at them you could see that they weren't all the same brightness.) So, now I'm working on developing my own tileable LED circuit boards and a driver board to keep them at a constant current (and brightness).

    You might have better luck with the strip-lighting. I think it's certainly a valid way to go.
     
    Last edited by a moderator: Aug 17, 2017
  3. Brindaloo

    Brindaloo Member

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    Hi John, it's been a while since you asked your question, but I'll take a whack at it, as I'm currently experimenting with building my own exposure units based on UV LEDs.

    My first exposure unit was a massive 2'X4' fluorescent tube construction that used 10x T12 40-Watt black light bulbs. (I believe they were GE 10526.) I found that, at a distance of about five inches, my standard printing time for full exposure of cyanotypes was around 45 minutes. This was with digital negatives printed on Pictorico OHP, the "original" cyanotype chemistry, and 3/32"-thick glass for my contact printing frame.

    Last year, I moved to NYC and couldn't take my fluorescent monstrosity with me, so I decided to build a much smaller unit based around UV LEDs. Lots of people have used cheap LED strip lighting from Amazon to build exposure units, so I tried the same. A 16ft length of "3528 SMD" blacklight LEDs cost me something like $20. They claimed to emit in the 395nm-405nm range. I made sure to buy a non-waterproof version, which came free of any silicone encasing. (I figured that the silicone encapsulant, though clear, would absorb a lot of the UV light, reducing the effectiveness of the unit. I also thought the encapsulant might yellow or become brittle with age.) I cut the long LED string into shorter strings, soldered wires to them, connected them in parallel, and attached them to an aluminum plate roughly 8"x10". The resulting array was quite dense. I only conducted a few tests with the finished unit, but found that my printing times had reduced to about 20 minutes. I think the key here (compared to my fluorescent unit) is that I was able to bring my prints much closer to the UV source. I designed a wooden box around the aluminum plate so that my prints were about 1" away from the LED grid. It was not possible to bring my prints this close to the UV source in my fluorescent unit--the light fixtures had big gaps between bulbs.

    In the end, despite the shorter printing times, I wasn't satisfied with my strip-lighting approach. My construction was a bit crude, and my LEDs never seemed to illuminate evenly. (Just by looking at them you could see that they weren't all the same brightness.) So, now I'm working on developing my own tileable LED boards and a driver board to keep them at a constant current (and brightness).

    You might have better luck with the strip-lighting. I think it's certainly a valid way to go. I think I gave up on it too soon.
     
    Last edited by a moderator: Aug 17, 2017
  4. tnp651

    tnp651 Subscriber

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  5. tnp651

    tnp651 Subscriber

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    This is my exposure setup. The UV light is suspended from a Lowell Scissor-clamp on the suspended ceiling, and a Lowell Pole.
    Exposure-setup-sm.jpg
     
  6. dlmorel

    dlmorel Member

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    Tom, What are your exposure times when using that setup?
     
  7. tnp651

    tnp651 Subscriber

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    With the light 30 inches from the contact frame, my times are 10-18 minutes, depending on developer and toner.
    Tom
     
  8. dlmorel

    dlmorel Member

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    Thank you! I am considering purchasing one. How large of a print can you make at 30 inches? Can you go closer and expose for a shorter time with say an 8x10?

    Thanks again!
     
  9. tnp651

    tnp651 Subscriber

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    There's no reason not to come closer for a smaller print, and of course your exposure time will be less. You'd need to test for that, of course. I'm standardized on 9x12" prints and coverage seems fine. You might see some vignetting at 16x20 based on the longer distance to the edges. You could use two lights to get a more even coverage.
     
  10. tnp651

    tnp651 Subscriber

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    I did some testing using an exposure meter. Photographic exposure meters aren't sensitive to UV but their response should be analogous.

    Here's what I found with my Quans light:
    9x12" print: 0.5 stop difference between center and edge of print
    11x14": 0.7 stop difference
    16x20": 1.5 stop difference

    Tom
     
  11. Bob Carnie

    Bob Carnie Subscriber

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    Quans Light - is there a larger unit more powerful??.. I love the concept of what you are doing
     
  12. tnp651

    tnp651 Subscriber

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    My 20W light is the biggest self-contained unit I found. There's this bulb https://www.cureuv.com/products/current-usa-gamma-40w-aquarium-uv-filtration-light but a) it takes a special socket and b) it's 254 NM wavelength. Kallitypes (and perhaps other alternative processes too) are most sensitive around 400 NM.
    Tom
     
  13. Bob Carnie

    Bob Carnie Subscriber

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  14. DennyS

    DennyS Member

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    Bob, Amazon is listing a QUANS 50W UV Ultra Violet LED Light for $85, but I think it would be important to contain the light, all that UV isn't good for your eyes.
     
  15. tnp651

    tnp651 Subscriber

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  16. SasquatchQB

    SasquatchQB Subscriber

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    I built my own similar setup, using two 5m strips of non-waterproof SMD5050 UV Led strip lighting hot-glued to a plywood board and wired in two sections through a 180W power supply. For gum bichromate, I ended up having print times of about 7 minutes, with the lights about 4 inches above the negative. Generally, it worked pretty well for the project I was using it for, but if I continue to do alt-process work seriously, I'll probably build something more robust.

    33365472_10155436045777927_7008677296043196416_n.jpg 33379061_10155436050247927_7913400676498014208_n.jpg
     
  17. Minas Stratigos

    Minas Stratigos Member

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