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  1. #11
    Curt's Avatar
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    I also noticed that the LEDs come in both 7000k and 3000k strips. Variable contrast head? Dimming of LEDs and edge burning possibility in the array?
    Lots of questions.

    Curt

  2. #12

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    Well, it wouldn't be very hard to hack up an LED VC-light source that would let you select the grade digitally. No more futzing around with filters.

    In fact, I've probably got most of the necessary bits sitting on my desk right now. :P

  3. #13

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    Paul, Jstraw, I simply have the wall transformer for the LEDs plugged into a GraLab 450 timer. For what it's worth, the GraLab is advertised as capable of handling inductive (fluorescent tube cold light) loads. I'm not sure if that pertains to the little AC/DC transformer for the LEDs, but so far I haven't had any problems with either the timer or transformer.

    The wall transformer I got from LEDtronics has the following rating: AC input 120 volts, 0.25 amps. DC output 12 volts, 1 amp, 12 watt maximum. The GraLab 450 just lists the following maximum loads: lamp 600 watts, or a resistive load of 1,200 watts.

    I'm glad to see some solutions to the LED 'fade'. I can best liken it to printing with a color head -- the fade of light from the bulb when it's turned off. I'm not too sure of myself to be dabbling with delicate electronics, so I've just been incorporating the 'fade' into the printing time. For me, it's nothing more complicated than making a test strip, deciding on a good time, then making a working/final print in the exact same manner and time as the test strip.

  4. #14

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    Curt, I chose the 7000K strips as according to the manufacturer they're the brightest they offer. The 3000K LEDs are much dimmer, about 1/4 as bright if I read their charts correctly. Using both wouldn't offer VC (7000K blue-white and 3000K dull yellowish color) and would get into problems with the brightness difference between the LED modules. The modules are one unit; and as my limited understanding of electronics goes, the LEDs are connected in series. I don't see a way to control each individual bulb for dimming and edge burning as you describe. Any dimming of the light would have to be applied to the entire strip of 12 bulbs.

    I think a larger 5x7 might be possible. I don't think the modules can be cut (at least I wouldn't!) as I see resistors built into the circuit boards of each strip every three bulbs -- I have no idea what cutting into the module would do to it. However, I think the 6" modules could be rearranged for a 5x7. Offhand I figure the head will probably have to be taller than the 4x5 I've built (to better diffuse the light out to the edges) and will need more than six light strips. I'll tinker with my setup and let you know ASAP about 5x7.

  5. #15

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    Hrm.

    You could always try wiring up the all transformer through the GraLab on the 12v DC side....

    Also (and I can walk folks through it if they want) you don't need to buy a strip, you can just get a perfboard from Radio Shack, some resistors, and some bare LEDs and make your own modules. Should be able make modules to fit any size that way.
    Last edited by wirehead; 12-07-2006 at 12:16 AM. Click to view previous post history. Reason: added a few more notes

  6. #16
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    Thanks all for the excellent answers to my questions. I am quite excited about the possibilities of using LEDs for a diffused light source. I was already looking for loose LEDs as wirehead had noted about making a board for use instead of strips. The strips though would simplify the work and seem to be a very good and well thought out process. A relay would be worth looking into with use of my existing timers.

    Thanks
    Curt

  7. #17
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    I think that someone here who is handy with electronics could make some money if he built a relatively cheap VC LED light source that was adaptable to the standard enlargers. The Calumet is > $1500 which seems awfully expensive for turning blue and green LED's off and on.

    I suppose the easiest way is to use the white LED strips mentioned here and then use below the lens glass filters for split contrast printing, but a head with both blue and green filters would be nice.
    Jerold Harter MD

  8. #18
    Lee L's Avatar
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    Quote Originally Posted by jeroldharter View Post
    I think that someone here who is handy with electronics could make some money if he built a relatively cheap VC LED light source that was adaptable to the standard enlargers. The Calumet is > $1500 which seems awfully expensive for turning blue and green LED's off and on.

    I suppose the easiest way is to use the white LED strips mentioned here and then use below the lens glass filters for split contrast printing, but a head with both blue and green filters would be nice.
    Jerold,

    I've been thinking about construction a light source for my D5 similar to the one in this thread, but using strips of blue and green LEDs from superbrightleds.com that are similar to the white ones used here. They have two kinds (one that snaps into shorter lengths) and they use half as many LEDs in the same space as the units in this thread. Given the times reported here, that light loss wouldn't be too problematic. UV or deeper blue LEDs might get more contrast.

    Lee

  9. #19
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    Do these LED's require any filtration in addition to VC filters? What is the right color temperature for a VC light source?

  10. #20

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    I haven't needed any filtration with the white LEDs other than my standard VC filter set. The light from the LEDtronics modules is a blue-white. Unfiltered, this light is the equivilent of a grade 3 (best guess) on my papers -- Kentmere VC RC and Agfa MC FB.

    5500K is 'daylight' and most tungsten/halogen bulbs are around 3000K. I suspect the right color for VC could be just about anything we want, just so long as we can get enough green, blue and UV in the mix that our papers are sensitive to.

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