What's a Watt or more?

Discussion in 'Darkroom Equipment' started by Shangheye, Mar 5, 2009.

  1. Shangheye

    Shangheye Member

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    OK...so I've had long exposure times when printing, and based on a few threads I decided to peak at my bulb to see if maybe there was a problem there (I bought it 9 months ago). I discovered that the installed bulb was a 60W soft white bulb, which did not match what I expected to be there...at least 75W incandescent. My negatives can also tend to be slightly thick so I don't know for sure the bulb is the issue.

    Anyway, I bought some Philips bulbs (75W enlarger ones), but I have been rather challenged by the idea, of what the consequence of this change is going to be. Should I expect that the relationship for exposure times is linear...i.e. I am only going to gain about a 25% reduction in my exposure times (in which case I am not sure it is worth it). Or are enlarger lenses substantially brighter? If they are not, why are they sold sepratately to say....soft white bulbs?

    Anyway, I keep notes on all my prints, but now I am wondering if all that work for the last 6 months is wasted? i.e. will paper grades be affected etc.

    I would love that it would be a simple ratio thing (i.e. the bulb is not a major issue), and I know I have to test this in the darkroom, but would appreciate any thoughts.

    Advice sought! Thanks.

    Kal
     
  2. Steve Smith

    Steve Smith Member

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    If they were the same make of bulb and all other constuctional details were equal then there could be a correlation between wattage and brightness but between different brands and types it would not be so easy to predict.

    A bulb produces more heat than light from the energy you put into it and the small percentage which ends up as light varies a lot.

    You have answered your own question anyway saying that you know you will have to test it.


    Steve.
     
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    Shangheye

    Shangheye Member

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    Thanks Steve. Can you (or anyone else) explain the difference between a bulb specifically manufactured for an enlarger and the soft white bulb installed at the moment, assuming all other things are equal? Rgds, Kal
     
  4. nemo999

    nemo999 Member

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    Among other things, an enlarger bulb is more heavily coated internally to give even illumination and does not have printing on the bottom!
     
  5. Ian Grant

    Ian Grant Subscriber

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    The Photo lamps are designed to give out a certain colour spectrum because some people use them for colour printing it's the whitening agent that they use that differs most. Most people now use dichroic colour heads but the nelarger bulbs will still probably better for VC papers.

    Ian
     
  6. MattKing

    MattKing Subscriber

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    In addition to Ian's point, enlarger bulbs tend to either have no writing on them, or have the writing on the side, so as to avoid the possibility of an image of the writing appearing as part of your prints.

    I've heard as well that the diffusion frosting in enlarger bulbs may be more even, but I've never verified that.

    Matt
     
  7. Jim Jones

    Jim Jones Subscriber

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    Cal, try measuring the light on the baseboard with a lightmeter and switching between the 60W soft white bulb and the 75 Watt Enlarger bulb. This should give you a close enough correction factor for the first tests on photo paper.
     
  8. srs5694

    srs5694 Member

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    One other issue is that a bulb's output varies over its lifetime. I don't recall whether it goes up, down, or and up-then-down or down-then-up curve, though. This can make duplicating results from months ago based on notes difficult. IIRC, tungsten-halogen bulbs don't vary as much over time as plain tungsten bulbs do.
     
  9. Bob-D659

    Bob-D659 Member

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    211(75w) and 212(150w) enlarger bulbs have fairly short rated lives, around 50-100 hrs IIRC. A std 60 watt is usually 1000+ hrs. There is substantial difference in light colour temp and output between a 211 and a std household bulb. A number of older enlargers mounted the bulb base up right over the lens, so you couldn't use a normal bulb unless you wanted the bulb logo in the middle of your print. :sad:

    The latest 211's I bought have a somewhat uneven coating on the sides of the bulbs, so I have to make sure the most opaque side is facing the condenser. I wasn't real happy to find a half visible image of the filament on a print the first time I used one of the new bulbs.
     
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    Shangheye

    Shangheye Member

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    Thanks all. It would appear at first test that the difference is about one stop in light which surprised me. Anyway, I will keep track of every different image to make sure I don't leap to that conclusion on each one. Thanks again. Kal