High output LED's for enlarger light source

Discussion in 'Darkroom Equipment' started by dogzbum, Aug 13, 2006.

  1. dogzbum

    dogzbum Member

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    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 :smile: ?



    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. resummerfield

    resummerfield Subscriber

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  3. Sparky

    Sparky Member

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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. Nick Zentena

    Nick Zentena Member

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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. Jon King

    Jon King Member

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    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.
    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.
     
  6. Claire Senft

    Claire Senft Member

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    Doesn't Calumet have an LED head that is in the works?
     
  7. Loose Gravel

    Loose Gravel Member

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    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.
     
  8. MurrayMinchin

    MurrayMinchin Membership Council Council

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  9. jford

    jford Member

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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. Donald Miller

    Donald Miller Member

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    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.
     
  11. Donald Miller

    Donald Miller Member

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    At that price, I think I will pass.
     
  12. Donald Miller

    Donald Miller Member

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    If any of you are considering doing this, Ebay has 1 watt and 3 watt blue and green Lumileds for sale. $3.99 each for the 3 watt units and 9.99 for five of the 1 watt units.
     
  13. Sparky

    Sparky Member

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    There's a much newer breed of high-output LEDs out now - I remember reading about it a few months ago - I can't recall any specifics - but it might be worth doing the legwork on google.
     
  14. Sparky

    Sparky Member

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  15. rmann

    rmann Subscriber

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    I have built a 4x5 LED head using 3 watt Lumileds and a buckpuck driver. There was a thread earlier this spring on it. It took a little longer to finish that I expected. Two problems I had to solve were light fall off in the corners with blue and heat. To even the blue light I ended up using the same number of green and blue LEDs. To solve the heat problem I added a fan to the head enclosure. It is working fine with very consistent exposures - it is at least two stops brighter than the Zone VI head I was using before. I have added a dimming function so that I can use longer times if needed. I would estimate that it cost about $400 for the LEDs, drivers, power supply, and assorted switches and components. If you like working on a project and have the time I would encourage you to go ahead.
     
  16. mcglamery9

    mcglamery9 Member

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    Earlier this year I built a 4x5 enlarger head using 8 royal blue and 12 green 1 watt batwing luxeon leds. You need more green than blue leds to get a consistent printing speed, although you will still have to slightly adjust the current thru each bank of leds. Also the royal blue will provide a slightly higher contrast range than the blue. Most people seem to be using the lambertian leds instead of the batwing. I used the batwings primarily because the luxeon web site stated that the batwing leds would provide more even illumination of a optical surface. My calculations verified what they stated but I haven't tested the lambertians. I mounted 16 of the leds in a 2.5 inch diameter circle, then added the additional 4 green leds right inside the circle. The leds I used were the bare emitters not the stars. They were attached directly to a heavy aluminum heat sink with thermal epoxy. The leds are about 5.5 inches from the diffuser. Hope this is helpful.
    Richard