New lamp dimmer than old?

Discussion in 'Enlarging' started by perkeleellinen, Feb 2, 2010.

  1. perkeleellinen

    perkeleellinen Member

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    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?
     
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  2. bsdunek

    bsdunek Subscriber

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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!
     
  3. perkeleellinen

    perkeleellinen Member

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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.
     
  4. ic-racer

    ic-racer Member

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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. AgX

    AgX Member

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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. Bob-D659

    Bob-D659 Member

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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. Bob-D659

    Bob-D659 Member

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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. AgX

    AgX Member

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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. AgX

    AgX Member

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    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. perkeleellinen

    perkeleellinen Member

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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.
     
  11. perkeleellinen

    perkeleellinen Member

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    A bit more information:

    The old lamp (Osram) has a vertical filament, the new lamp (no brand) is horizontal.

    The Osram is a 'HLX' lamp and I found the same model on ebay with the following description:

    http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=350246895181

    Possibly the difference in lamp brightness is a cause of the no brand lamp being a normal halogen and the Osram being a 'Xenophot'?
     
  12. perkeleellinen

    perkeleellinen Member

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    From some medical supplies site:

     
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  13. AgX

    AgX Member

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    Forget about that Xenon thing (indicated by Osram with HLX). It is of no importance to your problem, as the difference to the Krypton-filled lamps is only up to 10% gain in luminosity. And it is employed in standard and overrated ones alike.

    All those lamps we are talking about contain a Halogen.
     
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  14. paul_c5x4

    paul_c5x4 Subscriber

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    Rather than mail ordering, I'd suggest trying your local electrical wholesaler such as (picking two at random from the Oxford Yellow Pages):

    City Electrical Factors Ltd Unit 6, Oxford Trade Centre, Harrow Rd, Oxford

    Newey & Eyre Ltd, Curtis Yard, North Hinksey Lane, Botley

    You don't need to be trade, and if they are like my local suppliers, cash is just fine - Shouldn't be more than about £4 each.
     
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  15. perkeleellinen

    perkeleellinen Member

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    Before I read AgX's post above (and his pm) I went and ordered another lamp. This time making sure it's an Osram Xenophot. Not too sure if that was so wise now. But we'll see when it arrives.
     
  16. AgX

    AgX Member

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    The one Steve ordered seems to be the best choice. It bears the Osram number for an overrated lamp (50hours).

    Strange is that the dealer's code for this lamp is the same as for the substitute he already got...
     
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  17. pentaxuser

    pentaxuser Subscriber

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    Steve I'd be inclined to contact Nova. Unless they have changed a lot since I last used them, they will be interested and hopefully concerend that your lamp is that much poorer. If this is their standard lamp then presumably they can expect complaints from other customers so at the very least you will alerting them to a future customer problem.

    pentaxuser
     
  18. perkeleellinen

    perkeleellinen Member

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    Yes, calling Nova is a good idea. Firstly I want to make sure this new lamp is brighter then I can be sure I've solved my problem.
     
  19. perkeleellinen

    perkeleellinen Member

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    Problem solved. The Osram Xenophot lamp arrived and I fitted it this morning. Brightness is good and printing times are as expected (possibly a little more contrast).