Can I HID Lamp as cold light source !?

Discussion in 'Darkroom Equipment' started by andrew_hoi, Dec 27, 2010.

  1. andrew_hoi

    andrew_hoi Member

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    Hi all,
    I want to DIY my cold light source for my LPL7452.

    I found the HID lamp(the lamp for car ) have colour temp from 6500K to 12000K...
    Also, the stabilizer output fit with the HID power control gear...

    So, do anyone know, if I want to do this, which colour temp. good for this ?


    THX
     
  2. ic-racer

    ic-racer Member

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    Hmmm... lets see, characteristics of HID are, unstable color temp, unstable operating voltage through life cycle, heat generation, slow ignition, need for a ballast. I think they are good for illuminating baseball fields.
    I would rate HID lamps as probably the least suitable for photographic enlarging.
     
  3. onepuff

    onepuff Member

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    HID lamps are not suitable for enlarging as they are not "full spectrum" lamps. They emit light at a number of wavelengths which when combined give light at a given colour temperature but have significant gaps in their spectrum so will not render correct exposure results when using photographic paper.
     
  4. andrew_hoi

    andrew_hoi Member

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    OOO ic...
    I will give up the HID ...
    thx onepuff

    by the way, do the Fluorescent lamps produce full spectrum and suitable for BW paper ?
     
  5. Christopher Walrath

    Christopher Walrath Member

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    However, they do well as $200 headlights. Really.
     
  6. RalphLambrecht

    RalphLambrecht Subscriber

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    I never understood why cold light sources were so popular with some people anyway. They have few benefits and many disadvantages as far as I can tell. I find regular color heads or contrast filtration to be far superior.
     
  7. Curt

    Curt Subscriber

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    I agree; I was in the Aristo Cold Light head circle, owning several, but with major improvements in variable contrast paper several decades ago and the move to a color head had me asking why I needed a cold light head, tube type, at all. With built in dichroic filters and no limit to the intermediate settings, I see no need to go back to the cold light head. There have been a few things that have changed in photography as far as equipment availability and I've had to stop and evaluate each one for it's practical use. Two events happened; one is the availability of cheap color heads due to disuse in the industry and the demise of Aristo as a supplier. So I see color heads as a great diffusion light source with great adjustment controls.
     
  8. mike c

    mike c Subscriber

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    Curt,you don't happen to have any 5x7 cold lights hanging around that you want to get rid of,I can of need one.
    Mike
     
  9. ic-racer

    ic-racer Member

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    I have wondered about it also. My thought is that 'way back when' the coldlight had some advantages over the NON-Dichoric heads.

    With the advent of Dichoric heads, the coldlight does not compare so favorably. When you think about it dichroic filters are a pretty amazing concept. Heat and fade proof. Some people don't realize what a near-perfect light source they can make.
     
  10. Steve Smith

    Steve Smith Subscriber

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    It doesn't stop some people asking where they can get replacement filters from as theirs have 'faded' though!


    Steve.
     
  11. RalphLambrecht

    RalphLambrecht Subscriber

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    Steve

    My understanding is that dichroic filters are interference filters that selectively reflect the unwanted portion of the spectrum, passing only the desired color. Since the unwanted energy is reflected, and not absorbed by the filter, dichroic filters do not fade.

    http://en.wikipedia.org/wiki/Dichroic_filters

    However, if something is wrong with your filtes, It's probably easier to get a new (used) dichroic head than replacing the filters.

    If that is not successful, you can try here:

    http://www.dichroicfilters.co.uk/
     
  12. onepuff

    onepuff Member

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    Unfortunately, fluorescent lamps present a similar problem to HID lamps in that the light they emit is composed of several discrete wavebands. Fluorescents use a mixture of phosphors, each emitting a wavelength of light so they do not have a continuous emission spectrum. This is also the reason they tend to have a low CRI, even lower than most metal halide lamps.
     
  13. onepuff

    onepuff Member

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    There are a number of companies in the UK who supply dichroic filters and these can even be cut to order to suit a specific shape or size requirement. I have dealt with UQG before and they seem to be a good company. Others you may consider are http://www.comaroptics.com/ and http://www.knightoptical.co.uk/. There are more out there too.
     
  14. Nicholas Lindan

    Nicholas Lindan Advertiser Advertiser

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    Well, almost...

    A dichroic filter is a resonant cavity for light. It resonates at the pass/block wavelength - but also at sub-multiples. A bit like a musical instrument that produces not only the fundamental tone but also higher octave harmonics. A filter that passes at 700nM (deep red) will also pass at 350 nM (deep purple/near UV). This isn't much of a problem for most photo processes - though dichroics would make lousy safelight filters.

    To block the higher harmonics the filters incorporate an absorbing filter. This absorbing filter is subject to fade just like any other colored filter.

    The resonant cavity of a dichroic is made of very very very thin layers of metal and conductive metal oxides - so thin the metal is transparent. These coatings are subject to abrasion and corrosion if the protective over-coat degrades. Close proximity to a halogen lamp is a good degrader.

    Though they last a lot longer than wratten filters in the same duty, they are still subject to fade and degradation. It is not unheard of for them to need replacement. There is no need for precautionary replacement. When they fail it is quite apparent with blistering, peeling and mottling. Storage in high humidity environments, like the 10 years an abandoned enlarger can spend in the corner of a garage, can destroy the filters - but by then most of the enlarger will also be quite rusty and the lens covered in mold.
     
  15. mike c

    mike c Subscriber

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    For a B&W multi contrast head would they use a green and blue dichroic filters.
    ?
     
  16. Jon Shiu

    Jon Shiu Subscriber

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    They use same filters as color head, ie yellow, magenta, cyan.

    Jon
     
  17. mike c

    mike c Subscriber

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    Thanks Jon,I have a old chromega head that needs its gel filters replaced and was thinking of using dichroic filters to replace the gel filters.

    Mike