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  1. #1
    Curt's Avatar
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    LED or Halogen light source configurations

    I've seen enlarger light sources as covering a flat plane, such as cold light grids and LEDs in grid arrays. I've also seen halogen bulbs as light sources for "light boxes", a Styrofoam lined box with a hole for the light to direct in and diffuse onto a plastic, Plexiglas sheet. Older enlargers even had a bulb in a can with opal diffusing glass.

    I've read the threads here, contacted http://huws.org.uk/ and I have experience with Aristo Cold Light Heads, http://www.aristogrid.com/, and Beseler Color heads. I can't remember seeing an LED group in a light box that's Styrofoam lined.

    I'm making a diffusion light box with three halogen bulbs because I have the bulbs and holders with dichroic filters in red, green, blue from a Beseler head. What I'm thinking now is why wouldn't very bright LEDs work in place of the halogen bulbs. Also why wouldn't the right color temperature LEDs work without the filters? I'm making a light source for 8x10 but it would be the same design in other sizes.

    This is where I am at the moment, I would like others to input here with their ideas and requirements.

    Curt
    Everytime I find a film or paper that I like, they discontinue it. - Paul Strand - Aperture monograph on Strand

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    Jerold Harter MD

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    Curt's Avatar
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    Did you see this thread?

    http://www.apug.org/forums/forum43/5...roic-leds.html
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    Everytime I find a film or paper that I like, they discontinue it. - Paul Strand - Aperture monograph on Strand

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    Curt's Avatar
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    LEDs in grid form requires a large heat sink and is too complex for the causal diy'er. Split grade Aristo cold light sources are too expensive and are for black and white only. A diffusion mixing box can accept an external light source such as Halogen or the LED light that Steve points out. The Halogen is proven, the LED for a mixing box is not as of yet, as far as I know. I don't know how much heat it gives off, I imagine it would require a fan as does the Halogen. Halogen bulbs can be dimmed and there is the question of voltage compensation and color temperature in LEDs.
    Everytime I find a film or paper that I like, they discontinue it. - Paul Strand - Aperture monograph on Strand

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    There are MR-16 base LED bulbs that operate on 12 volts, but they don't provide anything close to the light from a 200+ watt Halogen bulb that's typical for the big enlargers, though 3 might work for your purposes. Superbright LEDs is one source http://www.superbrightleds.com/

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    Quote Originally Posted by bdial View Post
    There are MR-16 base LED bulbs that operate on 12 volts, but they don't provide anything close to the light from a 200+ watt Halogen bulb that's typical for the big enlargers, though 3 might work for your purposes. Superbright LEDs is one source http://www.superbrightleds.com/
    FWIW, I tried green and blue MR-11 bulbs from them in my Philips PCS130/150 enlarger. (This enlarger takes three 14V 35W MR-11 halogen bulbs; I only replaced the green and blue ones.) They lit up, but they were so dim by comparison to the originals that I'm sure the exposure times would have been ridiculous. (I didn't bother trying to expose paper with them, they were so dim.)

    Since I ran this test, though, the site has come out with a newer model that produces more light; however, this is a "white light" bulb, vs. the separate green and blue bulbs I used in my first test.

    I haven't looked at the MR-16 offerings all that closely, since my enlarger takes MR-11 bulbs.

    I've heard that LED technology is progressing rapidly, with light output doubling every few months. Thus, I figure it's only a matter of time (months to a few years) before LED bulbs that might function as drop-in replacements for tungsten or halogen bulbs in at least some enlargers arrive on the scene.

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    Quote Originally Posted by srs5694 View Post
    FWIW, I tried green and blue MR-11 bulbs from them in my Philips PCS130/150 enlarger. (This enlarger takes three 14V 35W MR-11 halogen bulbs; I only replaced the green and blue ones.) They lit up, but they were so dim by comparison to the originals that I'm sure the exposure times would have been ridiculous. (I didn't bother trying to expose paper with them, they were so dim.)
    It's possible that you could have reasonable exposure times as the light is the correct wavelengths for the emulsion. A huge portion of the light in filament bulbs is useless to the paper. You see it. The paper doesn't. It takes less of the "pure" color than you might think. Not very handy for focusing though.

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    Quote Originally Posted by JBrunner View Post
    It's possible that you could have reasonable exposure times as the light is the correct wavelengths for the emulsion. A huge portion of the light in filament bulbs is useless to the paper. You see it. The paper doesn't. It takes less of the "pure" color than you might think. Not very handy for focusing though.
    What I didn't make clear is that the PCS130/150 uses three bulbs, each with a filter (red, green, or blue), so the light is already dimmed in the out-of-filter wavelengths. Of course, it's possible that the filters let lots more light through than just the optimum, but still....

  10. #10
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    The newer technology LED's solve most of the concerns and lack of knowledge raised in this thread. Please do not confuse "brightness" with effective exposure illumination. Graded and VC paper emulsion are sensitive to light in very narrow wavelengths.

    A bright quartz halogen lamp produces a broadband spectrum. Very little of it's spectrum is in the desired bandwidths for B&W papers. Most of the energy from quartz halogen, (and other tungsten light sources, as well), goes to produce heat and red spectrum light. In many cases 80% or more of the energy from QH is heat. The QH light is filtered, either additive or subtractive to narrow the spectrum actually used in an enlarger head. The tubes in VC coldlight heads have filters, as well, to achieve the desired spectrum.

    As we all know you lose light with a filter and you cannot create a spectrum with a filter that is not in the originating light source.

    The newer, high-powered LEDís are available in very narrow light bandwidths. The Luxeon brands, as an example, produce approximately 80% of their light in +/- about 10 nm. LEDís are simple electronic diodes. The circuitry is dead simple. LEDís are devices that need current limiting. So, a typical grid array is serial terminated with a current limiting resister.

    LEDís, for our purpose, are exponentially more efficient in producing the desired light wavelengths. A suitably specified LED produces approximated 80% of itís light in the target wavelength compared to QH at about 3-5%. Again most of the energy from QH goes to HEAT!

    The heat LEDís produce is small, especially so when compared to the output. The critical heat management point is at the silicon chip juncture. Environmental heat is not an issue. With the number of LEDís that we need to produce the desired paper exposure, heat management is significantly less than required for the typical QH head. Excess head reduces the LED light output and decreases the expected duty life. It does not heat your darkroom!

    I am pretty excited about currently available LED technology. It is a growing technology, so the future, (pardon the pun!) is bright!

    Cheers,
    Geary
    Last edited by galyons; 07-07-2008 at 01:11 PM. Click to view previous post history. Reason: Hit "enter" too early!
    But your flag decal won't get you into Heaven any more. They're already overcrowded from your dirty little war.
    Now Jesus don't like killin' no matter what the reason's for, and your flag decal won't get you into Heaven any more. Ė John Prine

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