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  1. #1

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    New lamp dimmer than old?

    Here's an interesting problem I'd like some ideas on.

    I've got an LPL C7700 and I ordered a new lamp for it (12V 100W) as I wondered if I could obtain higher max contrast in B&W with a new lamp.

    When I put the new one in it seemed dimmer than the old, especially fully open when focusing. I took a neg I'd printed before and used the same exposure. The paper was blank! At first I thought my dev was exhausted but remembering the dimness I tried again with the lens fully open. This time I got a good image. Contrast was no different from the old lamp, mind.

    But the odd thing is why should a new lamp be 3 stops dimmer than the old one? I checked and double checked I'd mounted it properly. Then I put the old one back in and the image was brighter.

    Dodgy lamp?
    Is there some brightness grade on these things I'm missing?
    Any ideas?
    Last edited by perkeleellinen; 02-02-2010 at 04:57 PM. Click to view previous post history.
    Steve.

  2. #2
    bsdunek's Avatar
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    One is not really a 100W lamp? Could you have misread the markings on the old lamp? Is the new one a lower wattage in a 100W package? Are they both 12V?
    If they're both really 12V 100W lamps, you shouldn't be able to tell the difference. It is a puzzle!
    Bruce

    Moma don't take my Kodachrome away!
    Oops, Kodak just did!
    For all practical purposes, they've taken Kodak away.


    BruceCSdunekPhotography.zenfolio.com

  3. #3

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    The only difference between the two is the old one was made by Osram and the new one is an EFP. Both marked 12V 100W.
    Steve.

  4. #4
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    I recently did a multi-lamp shootout with my kids diffusion dichroic enlarger. I tried mulitple 50w, 75w, 80W, 12v 13v and 18v bulbs of different brands. The winning bulbs had a horizontal filament and the dim bulbs (all measured on the baseboard with an enlarging meter) had vertical filaments. Weather the lamps said "spot" or "flood" did not seem to matter as much as the filament shape.

    It was surprising because the 50W was 1.5 to 2 stops brighter than the 80W but boy the 80W sure did get hotter.

    So, I concluded that even though it is a diffusion head, the way the lamp focuses the beam on the first diffuser plate is very important to overall intensity on the baseboard.

  5. #5
    AgX
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    Maybe it was wrongly signed and packed. Meter the resistance.

    But ic-racer's idea on filament position is more convincing.

  6. #6

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    There are huge differences in light output of 100 watt halogen lamps. A 1000hr bulb can be the same colour temp as a 50 hour bulb, but the long life bulb puts out much less visible light.

  7. #7

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    Measuring the resistance won't help either, the resistance of tungsten goes way up when it's at operating temp in a filament, that's why bulbs go pop on startup, the inrush current is huge and vaporizes a weakened part of the filament.

  8. #8
    AgX
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    My experience so far showed that lamps of the same kind and the same wattage share the same cold-resistance.

  9. #9
    AgX
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    Quote Originally Posted by Bob-D659 View Post
    There are huge differences in light output of 100 watt halogen lamps. A 1000hr bulb can be the same colour temp as a 50 hour bulb, but the long life bulb puts out much less visible light.
    A "overrated" lamp will show a strongly reduced liftime, it will produce absolutely and relatively more light of the blue part of the spectrum and thus the colour temperature will show higher values.



    But you are right in hinting at the chance that Steve substituted a overrateed halogen lamp for a common halogen lamp. I did not think of that.

  10. #10

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    Thanks for the replies. All very interesting. The lamp I bought was from Nova Darkroom. I'm wondering if I should try another supplier and see if I have better luck.
    Steve.

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