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  1. #1
    Monophoto's Avatar
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    Spiral Bulbs - another question

    When compact fluorescent bulbs were first introduced, they were ungainly and generally didn't fit in most incandescent bulb applications. In addition, my recollection is that there were cautionary notes on the packaging that they could only be used in base-down installations.

    Those problems have all been overcome in the latest generation of spiral CFLs.

    OK, we are thinking about using spiral BLB CFLs to make a UV light box. All of the discussion I have seen has been around designs in which the bulbs are screwed into bases such that the axis of the bulb is perpendicular to the contract print frame. Hence, a valid consideration was the center-to-center spacing between bulbs.

    But as I look at spiral CFLs, it seems to me that there is more light emitted from the sides than from the ends. Wouldn't it make sense to arrange the bulbs so that their axis is parallel to the print frame? Has anyone every done this, and with what results? And the natural follow-up question - - - what was the spacing?

    Thanks

  2. #2

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    I'm not sure all those issues you mention have been cured. When I was looking at using them for an enlarger head I found a few things.

    1) The bulbs over a certain size don't like being enclosed. Heat becomes a issue. I think 28watts. That's one bulb. If you're using multiple bulbs I bet you need to worry about cooling even if the bulb is rated for enclosed fixtures.

    2) The bigger bulbs can only be burned bulb up.

  3. #3

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    I think that if I were going to consider getting an even light output from spiral bulbs I would probably look toward making a diffusion light box.

    By that I mean a box in which the lamp itself is not directly exposed to the paper much the same principle as light boxes used for diffusion enlargers.

    The problem thar arises when one considers bouncing the UV around is the reflective characteristics of the surfaces. UVA does not operate from the same reflective characteristics as light in the more visible realm.

    When I was doing some peliminary research into an Azo head for enlarging, I came across a material that was 96% UVA reflective. The name of this material was Mirro Silver, as I recall.

    All in all, for spiral bulbs, I think that diffusion holds a lot of promise.

  4. #4
    Photo Engineer's Avatar
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    When a spiral bulb is 'excited' at turn on, you see an initial flash of bright light that dies down to a lower level. Then light output increases gradually over a period of about one minute until it is constant.

    When you turn it off, there is a faint pinpoint bluish afterglow in the bulb.

    Overall, light wavelength seems to shift over the first few minutes of use.

    That is my take on these bulbs. We use them in most lamps in our home, but I would not use them in my darkroom lighting or in any exposing equipment.

    PE

  5. #5
    David A. Goldfarb's Avatar
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    These ramp-up/down effects can be avoided with any fluorescent source by letting it warm up, leaving it on and just inserting and removing the print frame.
    flickr--http://www.flickr.com/photos/davidagoldfarb/
    Photography (not as up to date as the flickr site)--http://www.davidagoldfarb.com/photo
    Academic (Slavic and Comparative Literature)--http://www.davidagoldfarb.com

  6. #6
    Photo Engineer's Avatar
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    David, of course I agree. I would feel remiss not having pointed this out though.

    In addition, one would have to measure the time needed to reach stability of hue and output for this to work. In a bank of bulbs, this would have to be adjusted for the slowest bulb to equillibrate.

    Actually, all vapor driven lamps such as sodium, mercury and a host of others using rare gasses all behave in a similar manner I believe and must be used photographically with care.

    PE

  7. #7
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    I made a light source using six of the BLB bulbs. Since I don't know any better, I pointed them down, put them inside a box painted white, screwed into the standard fixtures from the hardware store and accepted whatever spacing those fixtures allowed. It's about 2 1/2 inches. The ends are a couple of inches above the paper.

    I turn the bulbs on for about five minutes before beginning a session, then use a Graylab timer to turn them on and off. Exposures for 8x10 and 4x10 negatives originally made to print correctly on the last Azo Grade 2 now print on Vandyke brown in about 8-9 minutes. Exposure times are consistent over that period of time - I don't notice any variation from instability. My theory is that the exposure time is long enough for the variations to even out (at least for practical purposes). Nor do I notice any gaps from the spacing of the bulbs.

    juan

  8. #8

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    What you say is true but is no different from other light sources that people often use in alt printing, such as sun lamps,mercury vapor lamps, etc. What we must do with these type of lights is either give them time to warm up to maximum radiation, or even better, use them with a light integrator.

    Compared to regular tubes, however, this is one of the advantages of the spiral tubes. Regular tubes reach full output within just a few seconds of being turned on, whereas the spirals take about a 30-45 seconds by my testing with a light integrator.

    Still, I believe that it is theoretically possible to construct a lamp with the spiral tubes that will provide more output for a given area, and at less cost, than the tubes, assuming you make full use of the lamp with appropriate reflectors.

    Sandy

    Quote Originally Posted by Photo Engineer
    When a spiral bulb is 'excited' at turn on, you see an initial flash of bright light that dies down to a lower level. Then light output increases gradually over a period of about one minute until it is constant.

    When you turn it off, there is a faint pinpoint bluish afterglow in the bulb.

    Overall, light wavelength seems to shift over the first few minutes of use.

    That is my take on these bulbs. We use them in most lamps in our home, but I would not use them in my darkroom lighting or in any exposing equipment.

    PE

  9. #9

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    Still, I believe that it is theoretically possible to construct a lamp with the spiral tubes that will provide more output for a given area, and at less cost, than the tubes, assuming you make full use of the lamp with appropriate reflectors.
    I will soon be building my 4th UV light unit, this one the biggest yet, and am seriously considering the screw-in spiral bulbs. Sandy, how about a back-of-an-envelope rough design of how you would build one? What type of reflector material would you use and how would you space the bulbs?



 

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