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Thread: LED UV light box

  1. #1

    LED UV light box

    Hi There,

    I'm new to the group but am really interested in creating a UV lightbox for alternate process etc.

    Was just wondering if anyone has had any experience with UV LED's. I was thinking that making a lightbox with them could give a better light distribution and they don't consume anywhere near the power of the tubes.

    What kind of output and exposure time are people using?

    I'll try and post more info if anyone is interested.

    cheers,

    b.

  2. #2

    LED UV light box

    I have heard of high output IR led's because of night vision applications.

    I have not heard of high output UV led's, but that doesn't mean they don't exist.

    Most very high power ones are at visible wavelengths...you might search for large (1 W , 5W) visible LED's and you will at least find out whether same people make a UV version.

    The visible high power ones are still pretty expensive, drive can be much more complex than a power supply and resistor needed for ordinary LED's. They are usually active circuits with feedback and careful circuit layout/grounding requirements.

    Oh, I have seen some comments from people that the li'l UV led's (T-1-3/4 size, for example) are weak, but they may had poor specimens. There is a German company Roithner or similar name that has a wider range of wavelengths than I have seen from anyone else. They have numerous blues, etc. They may have UV ones. I don't think they were a great bargain, but they have some pretty special parts...like say you wanted 420 nm blue (still visible). I don't think anyone else makes them.

    I'll keep my eyes open in electronic mags & ask the DIY know-it-all at work.

  3. #3

    LED UV light box

    Hi Murray,

    Thanks for that, good info.

    I have found the LED's here: http://www.lsdiodes.com/shop/index.p...fd06d4eb2f10bb

    ... but as you say i'm not sure if the output would be enough. They are 5mm and have a wavelength of 395.

    I guess i need to get some and have a play around.

    Thanks again,

    b.

  4. #4

    LED UV light box

    Okay, they're rated at 500 millicandela -- that's half a candlepower, each (give or take around 2%, in this case). By comparison, a common visible high-brightness LED, two generations older than the modern ones used in flashlights, was 5000 mcd, or ten times the output. Modern high-output LEDs as used for lighting applications are probably at least ten times that output; those are bright enough to use in an enlarger in arrays of from four to a dozen or so, each, in blue and green (plus a few in red to whiten the light for easier focusing). Generally speaking, the redder the light, the more output you can get.

    On a cost basis, you're almost certainly ahead to buy either the spiral BLB fluorescents (the 27 W version would be my recommendation; they're about $20 each) or just get complete black light fixtures at lighting or home improvement store (or party supply stores), for about $18 each with a single 18" T5 tube rated at 13W.

  5. #5

    LED UV light box

    Ah ok, so you're saying that the tubes or bulbs would be better for price/coverage than the LED's?

    Good to know. Well it was a good idea at the time

    b.

  6. #6

    LED UV light box

    how about using the sun?

    it gives good coverage and is pretty cheap!

    has a certain artistic credability too!

    constantine

  7. #7

    LED UV light box

    Well, the problem with the sun is that it's unavailable if you print at night (as many working folks must). Worse, in some climates it's not reliably available even in daytime.

    The cheapest way to be sun-independent is to get a single spiral BLB and a clamp-on reflector lamp; for about $35, you can make a setup that will expose a cyanotype in under a half hour, any time the power is on, or you can make a minimal setup for around $20; either will cover 8x10 evenly, or larger prints at greater distance and correspondingly slower exposures.

    For around $100 plus some scrounged scrap, you can make a multi-tube setup using commercial black lights that will cover 11x14 easily and expose a cyanotype in ten minutes or so.

  8. #8

    LED UV light box

    Anybody tried a black/blue bulb in there enlarger? I was thinking about it for cyanotypes? Do you think it's possible?

  9. #9

    LED UV light box

    If your enlarger uses standard base bulbs, it's possible. I can foresee a couple problems that might or might not be surmountable. First, it'll be hard to focus; most lenses focus differently in UV than in visible, and your eye doesn't see very well in the extreme blue that's all the visible light the BLB fluorescents emit; this would probably yield to some testing of the lens for correct UV focal length, followed by careful adjustment of the focus setting after achieving best visual focus (or depending on a small aperture for DOF, but that plays into the other problem). Second, the light output of BLB is much smaller than that of white light sources, and the transmissive materials in the light path of an enlarger aren't selected for their UV transmission, which means the final output will be severely limited in brightness, and you'll need extremely long exposures for a slow process like cyanotype.

    I was contact printing cyanotypes today with a 13 W BLB in spun stainless reflector in a contact frame faced with plain soda glass (like in a window); at a distance from the print of about nine inches, to ensure even light over a 4x5, using cyanotype rex technique with ferric ammonium citrate sensitizer, I needed exposures from 20 minutes for a very thin 120 negative to 45 for a relatively thick 4x5. The exposure in an enlarger will be longer than that by a minimum of the magnification factor; in practice, the lens aperture and scattering from the negative will further extend the required exposure time.

    If there's more to the rex technique than I'm aware of (very possible, since I'm more or less re-reinventing it from the little snippets I've been able to glean on the web), it might be possible to confirm claims of printing fast enough to expose in camera or under an enlarger, but from what I've seen today, it's only, at most, about 2 stops faster than traditional cyanotype under BLB, perhaps an additional stop faster under sunlight.

  10. #10

    LED UV light box

    I only know what I think I remember asking Mike Ware about his Argyrotype formula and blue visible light.

    AFAIK, response should be ballpark similar to other iron-silver processes.

    He said process is somewhat sensitive to blue light adn people do get by that way...but no numbers for sensitivity (time).

    I have rambled at length on my thoughts about glass and acrylic blockage of long UV possibly increasing exposure times, with respct to whether or not to have a diffuser.

    It just occurred to me it's probably pretty essential to have a piece of glass to flatten the neg onto the alt-process paper. (Reality check for me). I guess 1 layer of glass is better than 2.

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