LED bulbs for safelights

Discussion in 'Darkroom Equipment' started by Kirk Keyes, Apr 15, 2008.

  1. Kirk Keyes

    Kirk Keyes Member

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    I'm looking to get some LED bulbs to use as safelights for making film speed emulsions. (I use Doran sleeves on fluorescents bulbs for regular darkroom work.)

    I currently have 2 Westinghouse 1 watt Nanolux bulbs. $10 or so. http://www.amazon.com/Westinghouse-Nanolux-1-Watt-Bulb-03469/dp/B000UQ1Y0Y

    This bulb works really nicely at about 3 ft from my work area when in a conical reading lamp housing, but I'd like something a little more powerful to cover more area. Westinghouse also makes a 3 watt version that I was thinking of trying, but I thought I'd see if anyone here has actually tried some LED bulbs.

    So, what have you tried and what did you think?
     
  2. David Grenet

    David Grenet Member

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    I make my own - at the moment I'm using 3 10mm LEDs, although I'm going to add more because I too could do with some more light.

    If you're handy with a soldering iron it really isn't very hard...
     
  3. paul ewins

    paul ewins Member

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    I'm using an OptiLED bulb mounted in the regular ceiling fitting. It is very bright but doesn't fog the paper. Unfortunately it is so bright that it is difficult to focus the enlarger because I can barely see the image on the baseboard.
     
  4. Lee L

    Lee L Member

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    Search APUG for "led safelight" and you'll come up with multiple threads with many individual suggestions for suppliers and set ups.

    Lee
     
  5. Ryuji

    Ryuji Member

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    Does anyone know if any of those LED bulbs come with ORANGE COLOR with peak spectrum at around 625nm?
     
  6. Anscojohn

    Anscojohn Subscriber

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    Paul, What color is your Optiled?

    John, Mount Vernon, Virginia USA
     
  7. Jon King

    Jon King Member

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    I use a 1W Luxeon Red LED, although Ryuji, it is spec'd with a dominant wavelength of 625nm. I rolled my own, powering it with a wall transformer through a resistor - it isn't an accurate currant source, but good enough for the application.

    I'm bouncing it off the ceiling of a 11x12 foot room, and it is bright enough to see well. It is bright enough I need to block it when using an EM-10 exposure meter. People coming into the room don't need much time for their eyes to adjust. Ilford MG paper was good for 8 minutes without fogging - I got bored testing after that.:surprised:
     
  8. Ken Nadvornick

    Ken Nadvornick Member

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    I made a simple light bar consisting of six 627nm-rated red OptiLED S-11 Festival mini-bulbs (http://www.lightworld.com/optiled/index.asp?id=5). This allows me to configure six different levels of brightness as needed.

    I then ran a safelight test using pre-flashed Ilford MGIV RC paper. I used a five-minute step resolution. The illumination level was sufficient during the test for me to read a magazine while I waited through 12 steps (60 minutes). After processing and careful examination, I could detect absolutely no fogging whatsoever. Oddly, however, the same test executed using Kentmere Bromide grade 3 showed fogging at the 20 minute mark. All tests were run with all six LEDs lit and located approximately seven inches from a 9-foot matt-white acoustical tile ceiling.

    Afterward, a cursory spectral analysis (using one of my son's CDs) did show a sliver of blue-green emissions from these bulbs. Apparently the Kentmere must be more sensitive to these residual emissions.

    Ken
     
    Last edited by a moderator: Apr 15, 2008
  9. RJS

    RJS Member

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    I am using two Optiled lights, I believe they are 625 in color - quite bright. I have them in cone shaped fixtures bounced off a fairly low ceiling. I ran tests as described in Beyond Monochrome (?) and found if bounced they are fine; aimed at Ilford MG from four feet they will fog after a couple of minutes. I process paper face down (I like to be surprised) and the safelight by my enlarger is switched off when the enlarger goes on so exposure to the safelight is brief.
     
  10. fschifano

    fschifano Member

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    Kentmere papers are quite fast.
     
  11. Ryuji

    Ryuji Member

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    Well, I have just made one using 3 orange LEDs with 625nm peak, driven by a simple current source (LM317) and will test if this plan works, but the reason why I'm so specific about this is that...

    I'm in process of making infrared sensitive plates. I've designed a dye mixture that gives sensitivity in 700-850nm, and this mix should also desensitize below 700nm.

    What this means is that I don't need an opaque filter, and I should be able to use a dark orange safelight with no deep red component. Conventional filter plus light bulb emits a lot of IR, so I can't use those. Orange LED is about the only thing I can think of that might work...

    I think for most printing emulsions, making a safelight with orange + red LESs may make more sense, but for my application, just orange...

    Ryuji
     
  12. paul ewins

    paul ewins Member

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    I'm using a red Festoon bulb - part# FS-B22-RD - and I also bought an orange one as well but haven't tried it as the red worked. That's with standard Ilford MGRC papers. I sat a sheet of paper on the enlarger easel with one half covered for twenty minutes. After processing both sides were the same base white. I don't normally take paper out of the box or paper safe until I am going to use it so that seemed good enough for me.
     
  13. Ken Nadvornick

    Ken Nadvornick Member

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    Yes, that would seem to be the case. Interestingly, that same Kentmere Bromide (from the same box) showed no fogging out to 30 minutes (where my testing ended) when the same test was run using my Thomas Duplex DUB low-pressure sodium vapor unit.

    Whereas the OptiLED bulbs are supposedly rated for a spectral half-width of about 20nm, I seem to remember reading somewhere that the sodium emission doublet (at 588.9950nm and 589.5924nm) show a combined half-width of something like only 2nm, with the next closest emission at 568.8205nm being only 0.7% the intensity of the stronger doublet line. If true, that's pretty darn pure light and may help explain the difference in fogging times.

    In any case, prints I make for eventual scanning and Web display are made under the red LEDs using Ilford MGVI RC glossy, as it scans much better on my older scanner. Keepers for display, however, are printed on the Kentmere Bromide under sodium light, which is so bright and cheerful it's almost stupid...

    Ken
     
  14. David Grenet

    David Grenet Member

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    Ryuji - as pointed out 'red' LEDs often have a 625nm peak value, 'orange' seems to be 600-610nm and 'amber' is 590nm.

    'Red' leds with a peak wavelength of 660nm are also available but seem to have a lower light output.
     
  15. PeterB

    PeterB Subscriber

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    Ryuji, if the mix continues to desensitize below 700nm, why not use yellow or green LEDs ? (uncomfortable on the eyes ?) The 625nm peak LEDs might just have enough spectral bandwidth to fog the emulsion at 700nm. In fact make sure you drive the LEDs at about half their max rated continuous current otherwise the emitted spectrum will spread out more than you want.


    Peter
     
  16. David Grenet

    David Grenet Member

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    In fact I'd be inclined to go all out and use RGB LEDs (making sure to use half the rated current and testing rigorously).

    Safe, white light!

    Btw good LEDs often have a data sheet which states the bandwidth (often at lower than max current) so you can have a better idea how safe they are...
     
  17. Nicholas Lindan

    Nicholas Lindan Advertiser Advertiser

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    Some LEDs have fogging problems and some don't. I've found a sheet of Rubylith needs to be placed over red LEDs to make them completely safe with all papers - without having to worry about the spectra of any particular LED.

    I haven't tried Amberlith in conjunction with orange LEDs, but it may work.

    For an OC look you may want to use both red and orange LEDs to have a broader but still safe light source.

    Of course, if bright enough, any light source will cause fogging.
     
  18. Ryuji

    Ryuji Member

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    I haven't actually tested the dye mix with emulsion yet. But based on the known properties of the emulsion and the dye, green will fog the emulsion very easily. Yellow is also close to the sensitivity limit of the emulsion.

    Another reason for orange LED of 625nm is that it is probably safe for ortho dyes like simple diethylcyanine. OC safelight will fog those ortho emulsions.

    Well, let's see what I find out with orange. If it fails, I may have to make a safelight with 3 switchable colors (yellow, orange and red) and pick one or two colors for each application I guess...
     
  19. PeterB

    PeterB Subscriber

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    A kit spectrophotometer.

    Here is an idea for a tool to help discern the spectral spread of various LEDs. A kit spectrophotometer.

    Prior to doing a paper fogging test, you could screen a bunch of LEDs from different manufacturers and at different drive currents using the spectrophotometer. That way you could potentially see which were the most likely to suit your needs prior to doing the paper fogging tests.

    I have bought one, and it is quite a novelty. You calibrate it by pointing it at a fluorescent light and lining up the scale to a specific green emission line at 546nm.

    Peter
     
  20. Ryuji

    Ryuji Member

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    I set up 3 orange LEDs of 625nm peak in my darkroom, and did some fogging test. I drove them at 50mA (when abs max rating is 75mA), and it's soldered on lots of copper lands for heat sink. The LEDs were about 50 cm away.

    First, I used silver iodobromide emulsion of daylight speed about 800. The safelight fogged emulsion very badly (not usable at all).

    Martin from alt-photo list (which is a very good resource) warned me that those orange and red LEDs have undocumented green emission, so I put on a red gel filter (I buy a sheet of 20x24 and cut it out for various uses... such as covering up my iPod, Treo and sometimes MacBook when I work in darkroom). This filter has less than 1% transmission below 600nm, and only about 25% transmission at 625nm. With this filter, fogging is lighter but it still fogs... while regular OC safelight and sodium vapor safelight did not fog this emulsion as badly.

    (Of course, I tested with fast emulsions, so this result may not apply to most printing emulsions, which are 100x slower than this emulsion.)

    I think the problem is that this LED safelight is quite bright. Even emulsions without spectral sensitization have some red sensitivity if heavily sulfur sensitized (although this is far too slow to be useful for photographic purposes) and this may be playing a role here.

    Lesson: even if you use LED for the light source for safelight, make sure to use it at a normal safelight illumination level. (how obvious!)
     
  21. PeterB

    PeterB Subscriber

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    This is very useful information Ryujii. Can you supply a part number for the LED's you used ? I'm curious to know who manufactured them so I can see the datasheet. Agilent have a good reputation for small values of FWHM. However some dodgy companies who don't care about manufacturing to their published specs have much wider spectral emissions (FWHM).

    Peter