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  1. #11
    polyglot's Avatar
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    The other option is bicycle tail-lights, bought online for about $2 each. They're red LEDs and quite paper-safe. You can run them for a few sessions on a pair of AAAs or wire them up to a 3V plugpack for infinite life.

    I just leave a 3-LED one on top of my enlarger head facing upwards at the ceiling for diffusion through the room; two or three bounces are required for light to hit the easel. It's plenty of light - I can read the 6-point text on the keys of my f/stop timer.

  2. #12
    clayne's Avatar
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    There's previous threads on this. Been using superbrightleds.com LED safelights for a few years myself. Zero issues with fogging. I use the red ones, bounced off the ceiling.
    Stop worrying about grain, resolution, sharpness, and everything else that doesn't have a damn thing to do with substance.

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  3. #13
    BetterSense's Avatar
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    When I built my LED safelight I had separate dimmable amber and red luxeon LED; but it turned out that I can have a much brighter red LED and still be safe, so I hardly use the amber anymore.
    f/22 and be there.

  4. #14
    Ken Nadvornick's Avatar
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    Quote Originally Posted by domaz View Post
    I would be careful with the Amber LEDs. I used a Luxeon Rebel Amber LED (e.g. very high power model). It's supposed to to have a wavelength range of 584-597, yet it fogged the heck out of paper at 5 feet away. These are extremely powerful LEDs though so I think the light level may have been a bit much.
    As I've posted before, some LEDs do emit wavelengths significantly outside of their rated ranges. That, not overall brightness, is usually the cause of residual paper fogging. And as one would expect, the more powerful the LED, the greater the fogging that occurs.

    Try this. Go find an old CD somewhere. Turn on your LED and observe its light as reflected off the recording side of the CD, which acts as a poor man's prism. If you look closely I'm betting you'll see the real cause of your fogging. When I did this using my 635nm red LEDs I noticed small, but very distinct, spikes of blue and blue-green light. That explained the light fogging I was seeing.

    After mounting my LEDs under a single sheet of Rubylith the spikes, also as one would expect, disappeared completely. And so did my light fogging. As I've mentioned before, I then performed the pre-flashed paper fogging test (using Ilford MGIV FB/RC) and absolutely could not fog the paper even out to 60 minutes of direct exposure. I stopped the test as being pointless beyond that. Perhaps you could do the same or similar with Amberlith? Or the Roscoe filter described below?

    This situation is analogous to the claims that the Thomas Duplex low-pressure sodium safelights fog paper because "they're just too bright." Nonsense. If the frequency range of the safe light being emitted does not overlap the paper's sensitivity range, the paper will not fog when exposed to that light, no matter how bright it is.

    But the Duplex, like the LEDs, also emits at frequencies other than the (safe) doublet. These include numerous blues and greens, with one sizable spike just below 570nm.* Instead of using Rubylith, these can almost all be eliminated by filtering through an inexpensive sheet of Roscoe #19 Fire theatrical gel.** I've also done this in my darkroom and have tested a fully open Duplex using Kentmere Bromide graded paper out to 30 minutes with absolutely no detectable fog.

    Ken

    * See here for an example of a real world line spectrum of an unfiltered low-pressure sodium vapor emission formed through a 1mm slit. (Fourth item down the page, click on the third panel.) Note that everything to the left of that bright orange output (the doublet) is capable of fogging various b&w photo papers. Even though your unaided eyes cannot see them, similar outlying emissions can also occur with some LEDs.

    ** See here for a graph showing the absorption/transmission characteristics of the Roscoe #19 Fire filter.
    Last edited by Ken Nadvornick; 07-05-2012 at 02:30 AM. Click to view previous post history. Reason: Added Thomas Duplex example...
    "They are the proof that something was there and no longer is. Like a stain. And the stillness of them is boggling. You can turn away but when you come back they’ll still be there looking at you."

    — Diane Arbus, March 15, 1971, in response to a request for a brief statement about photographs

  5. #15
    Rafal Lukawiecki's Avatar
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    I can second that not all red LEDs are safe. Using the CD/prism test, I could see that of the three red LEDs, which I have tried, all have differing amounts of non-red ingredients, green mainly, when refracted this way. My current one is a rather very bright, powerful 4W red LED. Using the Kodak safelight test (http://motion.kodak.com/motion/uploa...light_1106.pdf), I was getting fogging at even a 1 minute exposures to the LED safelight, which was pointed at the ceiling, about 2m away. However, having dimmed it by means of an ND filter made out of an exposed/processed sheet of film (transmission density 1.4), it passes the standard Kodak test and is safe up to a 14 minute exposure. It is still very bright, much more than any other safelight I had before.

    I will try a different make, lower wattage red LED bulb, with and without a standard red safelight filter, some time this month.
    Rafal Lukawiecki
    See rafal.net | Read rafal.net/articles

  6. #16
    baachitraka's Avatar
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    Quote Originally Posted by polyglot View Post
    The other option is bicycle tail-lights, bought online for about $2 each. They're red LEDs and quite paper-safe. You can run them for a few sessions on a pair of AAAs or wire them up to a 3V plugpack for infinite life.

    I just leave a 3-LED one on top of my enlarger head facing upwards at the ceiling for diffusion through the room; two or three bounces are required for light to hit the easel. It's plenty of light - I can read the 6-point text on the keys of my f/stop timer.
    I use the same(tail-light) which have four LEDs that take 2xAAA.
    OM-1n: Do I need to own a Leica?
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  7. #17

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    I have to wonder if the "out of spec" wavelength described by Ken may be due to sample-to-sample variations as opposed to design specs.

    Good to know about the Roscoe gel for the Thomas Duplex. One sheet will easily do both filters.
    "Far more critical than what we know or do not know is what we do not want to know." - Eric Hoffer

  8. #18
    polyglot's Avatar
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    Quote Originally Posted by mgb74 View Post
    I have to wonder if the "out of spec" wavelength described by Ken may be due to sample-to-sample variations as opposed to design specs.

    Good to know about the Roscoe gel for the Thomas Duplex. One sheet will easily do both filters.
    No, LED wavelengths are a function of the chemistry used; you get one wavelength for each electron bandgap in the semiconductors used. You can get variations in relative intensity of the different wavelengths between batches due to varying mixtures of dopants, but the presence or lack of a particular wavelength is all down to the chosen dopants.

    Different brands will have different selections of wavelengths (chosen from a handful of basic chemical options); if one LED from a brand has a bunch of parasitic emissions then all of them will. Likewise for a monochrome LED, all the LEDs of that design will be monochrome.

    White LEDs are an exception as they are based on a phosphor excited by an UV LED, so they have a weirder spectrum that's much more subject to tweaking and variation.

  9. #19
    Lukas_87's Avatar
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    The most effective contemporary white LEDs are actually based on blue InGaN (indium gallium nitride) LEDs (usually epitaxial layer on top of the SiC substrate), rather than UV LEDs. but that's bit irrelevant to the topic, sorry...
    Last edited by Lukas_87; 07-06-2012 at 05:09 AM. Click to view previous post history. Reason: typing error

  10. #20

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    I'm an overkill guy. I built a safelight using both red and white LEDs from superbrightleds which are then filtered through Kodak safelight filters. For an extra few dollars I also put a dimmer on it (pulse width modulation dimmer from superbrightleds). I've tested safe times with my Ilford paper out to 45 minutes for fun. No fogging. Didn't bother testing longer. I get very long safe times for Ortho films too, which is very handy for making masks.

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