My LED Darkroom Safelight

Discussion in 'Darkroom Equipment' started by twalsh341, Dec 16, 2012.

  1. twalsh341

    twalsh341 Member

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    Today I decided to get those parts I had laying around into a useful darkroom. I boarded up the bathroom window, make some workspace and then wend to Radio Shack to get some components for the LED safelight I wanted to make. I wanted to go LED because they put out a specific wavelength, in the case of red, my LEDs are about 640 nanometers (I forget the exact figure but it's -+10 nm). I used 2 1W high power LEDs powered by a 9V battery, calculators online can tell you how big a resistor is needed given the arrangment of LEDs and the power requirements of source and forward voltage etc. I popped all the junk into a project box with a switch and there we go. Its really bright and shows no signs of fogging the paper I was cutting and getting ready so far. It's bright enough that it lights up the whole bathroom when placed on the closet door, bouncing off the ceiling.
     

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  2. Ken Nadvornick

    Ken Nadvornick Subscriber

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    Nice job!

    When you get a chance, you may want to go find an old CD/DVD and observe the red light as it's reflected off the recording side of the disc. The disc will act as a simple prism and break the light up into discreet color bands.

    Look closely and make certain your LEDs are not also emitting small slivers of blue and/or green light. Too faint to see with the naked eye, but enough to sometimes cause slight fogging in your print highlights. It's not unusual for red LEDs to do this, regardless of what the specs say.

    My 635nm red LEDs showed both blue and green spikes. If yours do as well you may need to add a single layer of Rubylith as a filter. This will fix the problem. Also make sure you perform a pre-fogged safelight test with whatever paper you are using.

    Ken
     
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  3. twalsh341

    twalsh341 Member

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    Ken,

    Thanks for the tip, I checked with a DVD and unless I'm doing it wrong it's only emitting red. Which is great, because I went through this whole process to avoid having to use filters and that sort of thing.
     
  4. fran

    fran Member

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    A friend advised me to do the kodak safelight test. Well worth doing and more accurate than a simple coin test.


    BTW, I made a similar one to yours, I used regular red LEDs and I made an array with 24 of them running of an old wallwart. I put them in a red aerosol can lid and it passes the safelight test.
     
  5. Ken Nadvornick

    Ken Nadvornick Subscriber

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    Probably not. If the spikes are present they're pretty obvious. Small, but obvious. I noticed mine right away. So have most others who have seen and reported them.

    Sounds like you are good to go.

    :smile:

    Ken
     
  6. Rafal Lukawiecki

    Rafal Lukawiecki Subscriber

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    I'm with Fran on this one. Please do the Kodak test, it will only take 10 minutes and it will save out $$$ in paper, but above all, in frustration spent in chasing good contrast. The test is here: http://www.kodak.com/global/en/consumer/products/techInfo/k4/k4TestSafelite.shtml

    Coin test does not tell you the full picture. You may have a safelight that passes it, but which can still fully depress the highlights in your prints, causing you to overcompensate with high contrast settings.

    Second to this, in importance, is making sure your enlarger does not leak too much light.

    Well done for building such a neat device.

    Ps. My LED safelight works but it required an addition of a red filter. LEDs differ, and even the purest deep red, as checked by the CD/prism test mentioned by Ken, will affect paper if too bright.
     
  7. john_s

    john_s Subscriber

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    I have made a few LED safelights and I have never found an orange or red LED that emits anything like a single wavelength. If yours pass the CD test showing red only, can you tell us the part number please?
     
  8. michael_r

    michael_r Subscriber

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    Thought I'd post DIY LED safelight "Mark II" as it was a fun little project.

    It takes 8"x10" filters. Shown is a Kodak #1. Note I used Kodak filters because I was able to get a few recently for a song. Otherwise they are ridiculously expensive so you'd be better off with some Rosco or Lee gels or something.

    The pictures show the safelight with the red LED board installed. I would use either a Kodak #1 or #2 for ortho film (masking). The #1 works well for printing too. But I still tend to prefer the good old Kodak OC for printing so I made an identical LED board with warm white LEDs. I can slide that one in and use a Kodak OC filter.

    The "electrical work" for this is essentially plug-and-play for dummies from Superbrightleds.

    The dimmer works by "pulse width modulation" so that spectral output is constant regardless of dimmer level.

    These LED safelights are fun projects but as others have noted, always do proper safelight tests. These cheap red LEDs are not as sharp cutting as one might expect, nor do these particular red LEDs peak far enough into the red spectrum as I'd like. Superbrightleds does offer another red that peaks at 660nm with a fairly narrow band, but they are not plug-and-play (require soldering etc) so I didn't bother. Since I had the Kodak filters anyway, putting a #1 or #2 over red LEDs makes for very long safe times.

    Michael
     

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  9. scheimfluger_77

    scheimfluger_77 Subscriber

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    Michael,
    That is stinkn' simple, and to think I sweated so long waiting for the right deal on a Thomas safelight :sad:

    Thanks for sharing the project.

    Steve