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  1. #1
    dogzbum's Avatar
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    High output LED's for enlarger light source

    I'm considering using Luxeon (or similar) 1W, 3W, or 5W LEDs to make a light source for a 5x7" enlarger. These apparently produce around 75 lumens per Watt. As generic brand versions are reasonably cheap it may be more affordable (for me) to buy 10 or 20 of these than import a cold cathode source.

    Note my reasons for doing this are to reduce heat and for better control as the current light source is not stabilised.

    I was specifically thinking of using 10 blue and 10 green, each bank separately dimmable for variable contrast filtering. The wavelength specs for the LEDs are below. (See also http://www.luxeon.com)

    Questions:
    • Has anyone built or can anyone see fundamental problems with using high output LEDs for enlarger sources?
    • How do I calculate how many I will need? What is typical output level (in lumens or similar) of cold cathode head for 5x7" enlarger?
    • Has anyone got plans for building one :-) ?




    LUXEON 3 Watt LED Star Modules
    *Viewing Angle: 160 degrees
    *Wavelength or Colour Temp:
    Colour Min. Typ. Max.
    Blue 465nm 470nm 475nm
    Green 520 nm 530nm 550nm

  2. #2
    resummerfield's Avatar
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    There has been some discussion on this site (http://www.apug.org/forums/showthrea...&highlight=hew ) about the LED light source. Hew Finney (http://www.textklick.demon.co.uk/ledhead.html ) built up the best VC LED head I've yet seen. He suggested about 30 of the 3w LEDs (18 green and 12 blue) would be ideal for 8x10.
    —Eric

  3. #3
    Sparky's Avatar
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    I really CAN'T see how any density of those can be bright enough - at least for enlargements beyond 2X. Wouldn't you start really getting into reciprocity problems?

  4. #4

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    One thing is you don't have any wasted red light. Plus use enough of them and it all adds up.

  5. #5
    Jon King's Avatar
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    Quote Originally Posted by dogzbum
    Questions:



    • Has anyone built or can anyone see fundamental problems with using high output LEDs for enlarger sources?
    I don't see any fundamental problems. I've built a 6x9cm head with 2 3W lumileds (2 green, 2 royal blue), into a mixing chamber. Exposure times are comparable to the tungesten head it replaced. My goal is to also make a 5x7 head. On the Internet, Huw Finney's pages are the best source I've seen, and there is a good deal of design work he did there to get them working well.
    • How do I calculate how many I will need? What is typical output level (in lumens or similar) of cold cathode head for 5x7" enlarger?
    • Has anyone got plans for building one :-) ?
    One approach could be to take Huw's design with 1W leds and replace them with 3W ones. Times should be similar to what he got, but the real problem is heat dissipation. The total power is not high, compared to a tungsten bulb, but the area that generates the heat is very small - without a good thermal design, the LEDs will get quite hot, and their output falls when hot, by a significant percentage.
    Jonathan
    -----------------------------------------------

  6. #6

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    Doesn't Calumet have an LED head that is in the works?
    Claire (Ms Anne Thrope is in the darkroom)

  7. #7
    Loose Gravel's Avatar
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    Quote Originally Posted by Claire Senft
    Doesn't Calumet have an LED head that is in the works?
    Seems as though it will always be in the works.

    Designing a LED enlarger source is quite a problem and I don't know what you've solved when you are all done. Also, if you have one of a kind equipment, you will be the one fixing and troubleshooting.

    The disadvantages of LEDs are:

    Blue light is 450nm. This isn't that blue for VC paper. 400 nm would be better.
    LEDs' light output is temperature sensitive.
    Green LEDs are more temperature sensitive than blue.
    LEDs' light output is age sensitive, although not great.


    These things mean that you will probably need some kind of stabalizer for light output. You may have a hard time reaching the high (4 - 5+) grades of VC paper do to the lack of 'true blue' in the blue LEDs. Getting the illumination even will be difficult and lossy. Expect a factor of 2x loss in brightness as a minimum. Finally, with enough LEDs to make this work, thermal management will be a bugger.

    It is doable. You will need to be a circuit designer, PCB/thermal designer, and a few other things. Probably easier to buy a coldlight, a stabalizer, and a pack of filters. You'll be printing sooner.
    Watch for Loose Gravel

  8. #8
    MurrayMinchin's Avatar
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    It seems Calumet has finally figured it out, and it's now available;

    http://www.calumetphoto.com/item/EN6400.html

    They used 24 1 watt emitters for a 4x5 light source.

    Murray
    _________________________________________
    Note to self: Turn your negatives into positives.

  9. #9

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    The use of Luxeon 1W LEDs requires very good thermal management, not to mention the use of 3W or 5W units. Most of the light fittings I've seen using these LEDs have the PC board laminated to a piece of aluminium at least 2mm thick as a heatsink. If you're enclosing the LEDs in any way then the heat control needs to be better. I think cooking these LEDs might be an expensive thing to do.

    John.

  10. #10

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    Quote Originally Posted by Loose Gravel
    Seems as though it will always be in the works.

    Designing a LED enlarger source is quite a problem and I don't know what you've solved when you are all done. Also, if you have one of a kind equipment, you will be the one fixing and troubleshooting.

    The disadvantages of LEDs are:

    Blue light is 450nm. This isn't that blue for VC paper. 400 nm would be better.
    LEDs' light output is temperature sensitive.
    Green LEDs are more temperature sensitive than blue.
    LEDs' light output is age sensitive, although not great.

    One could go to the Luxeon Dental. Since it is used for dental curing, it is probably into near band UV and that will give a ton of contrast and rapid printing times on photo paper.
    Art is a step from what is obvious and well-known toward what is arcane and concealed.

    Visit my website at http://www.donaldmillerphotography.com

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