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Thread: Film sensitivity to GraLab clock glow

  1. #31

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    Re: Film sensitivity to GraLab clock glow

    Whoops! Correction on last comments:

    "Conclusion: Safelight (or more powerful Luminox Watch) glow should be safe..."

    I meant to say TIMER, not safelight. I would not recommend sticking exposed, unfixed film under your safelight! I don't think it'll hold up to that!

  2. #32
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    Re: Film sensitivity to GraLab clock glow

    Cletus,

    You're conclusions regarding the safety of the glow from a luminous dial are the same as mine (see post #4 in this thread).

    A few years ago, I purchased a new GraLab 300 timer (the one with the gray plastic case) and noticed that the dial and the hands glowed much more brightly than my old black metal-cased GraLab 300.

    Tested it after charging with florescent light to make it glow as brightly as possible.

    It fogged film at the contact point where I held it directly against the luminous dial. It fogged paper only after holding it there for a much longer time.

  3. #33

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    Re: Film sensitivity to GraLab clock glow

    I have used a Gralab for many years with no fogging. My Graylab is about three feet from the developer tray on a shelf above my sink. However, I am using a newer Gralab timer now (the type made of plastic) and the luminosity is so weak (the opposite of what another poster here reports) that with the room lights off I can hardly see the Gralab after a couple minutes. I attached little pieces of luminous tape on the dial and hands. That was REALLY bright - so bright that I was concerned. I could actually see my hands and the trays once my eyes acclimated to the dark. So, I cut the luminous tape with a razor blade that I had attached to the timer and removed most of the tape so that they were about 1/3rd the size I had orginally made them.

    A couple of other related comments: The inverse square law of light law really applies to point light sources. The luminous dial of a Gralab timer isn't a point light source but, for practical purposes, the rule is still useful. However, the Inverse Square Law was described incorrectly in page one of this thread and that should perhaps be clarified. Light intensity is not 1/9th of what it is at the light source when measured at three feet from the light source or, in another example, 1/4 of the intensity at two feet from the light source as explained. If it was, what would it be at 3 meters from the light source? It wouldn't be 1/9th of the intensity obviously. You have to start with a distance from the light source, not the light source itself. So, for example, say light intensity was X at a given distance from the light source, it would be 1/4 of that intensity if you doubled he distance. If you tripled the distance, light intensity would be 1/9th of what it was at the initial distance. In other words, it applies to the difference in two distances from the light source, not the distance from the light source itself.

    Lastly, remember that if you get slight fogging of the film, it can usually be burned through with no problem when printing. In other words, printing time may just be slightly longer. However, fogging can also reduce contrast just as it can when you pre-fog film or paper so you may have compensate for that - or you may already be doing it without realizing it. My base + fog densities have never shown any fogging over the years when processing in open trays with a Gralab about three feet from the developer tray. However, that could be simply because any fogging didn't reach the threshold of the film but it may have fogged the low density areas. If it is, it has never been a problem and my calibration is compensating for it. It would be interesting to test this just out of curiousity. Maybe I will do that the next time I test a film.

    BTW, I developed some film last night with my REALLY bright tape added to my Gralab and it doesn't appear to have caused a problem but I didn't test it so I can't say for sure. But they look good and are certainly printable. I have already removed most of the tape, though, because it really was bright. The tape I used supposedly glows for 24 hours once charged. I don't know about that but it sure glows a lot better than my newer-style (plastic) Gralab which, as I said, I almost couldn't see after a few minutes of dark.
    Last edited by ZoneIII; 21-Sep-2010 at 13:42.

  4. #34
    Cordless Bungee Jumper Sirius Glass's Avatar
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    Re: Film sensitivity to GraLab clock glow

    Quote Originally Posted by jonathan_lipkin View Post
    I'd agree with everyone above. I had a gralab timer directly above my sink where I would tray develop 4x5 sheet film and never had any problems.
    My experience too.

    Steve
    Nothing beats a great piece of glass!

    I leave the digital work for the urologists and proctologists.

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