Film sensitivity to GraLab clock glow

[Gem Singer]

Vlad,

My makeshift darkroom is located in a large walk-in closet adjacent to the master bathroom in my house.

The florescent ceiling fixture was installed when the house was built. It was not my choice. However, no need to replace it. I just don't use it when dealing with light sensitive materials in that space.

[aduncanson]

What I don't really understand is why you would use fluorescent tubes in the darkroom. They take minutes to reach their full power, glow for minutes after being turned off, and give an ugly light which makes assessing prints difficult. Why would you want them in your darkroom?
I know they have some benefits, and I use a lot of them in my house. Just not in the darkroom.

Maybe it is because I do most of my enlarging with a cold light head.

I thought about this pretty thoroughly and decided that it was a compromise I could live with. New "Full Spectrum" fluorescents are not perfect, but actually give pretty nice light for evaluating B&W prints, (I like to assess and view prints quite well lit.) make very little heat, and do not exhibit appreciable delay in reaching full brightness. The glow certainly does not affect my enlarging or contact paper, and as I indicated I have a simple and perfectly effective way of avoiding any problem they may cause with film.

[Jerry Bodine]

What I don't really understand is why you would use fluorescent tubes in the darkroom. They take minutes to reach their full power, glow for minutes after being turned off, and give an ugly light which makes assessing prints difficult. Why would you want them in your darkroom?
I know they have some benefits, and I use a lot of them in my house. Just not in the darkroom.

Vlad,
I installed fluorescents mainly because they generate much less heat than incandescents. I don't use them for print assessment, and they are turned off during a printing session, but I use the room for other activities as well and the light output is not objectionable. Regarding the heat, I can control the temperatures of my chemicals when prepared in the trays for printing, but over the course of a long printing session the room temp can sometimes increase by over ten degrees, necessitating the use of the sink as a water jacket to maintain 20C in the solutions for consistency. So my intent is to minimize the generation of heat in the relatively small room size.

[Harold_4074]

Looked up and noticed that the two forty inch florescent tubes in the ceiling fixture were still glowing dimly. Probably would have fogged fast film had I exposed it to that glow.

Could you take a picture of that and post it for us?

I'm being facetious, but only partly---if you tried to deliberately make an image in the lowest light levels that you eyes can detect, the reciprocity correction would probably try the patience of a statue.

Like just about everyone else, I have been startled to discover that the timer that I have been using for years can provide enough glow for me to distinguish objects while I am developing film, and my darkroom "white light" is only two 40-watt bare incandescent bulbs, so supercharging the phosphor by fluorescent is not a factor. Film supposedly loses much of its sensitivity as it develops (which makes develop-by-inspection practical) so that helps as well.

I actually wonder if perhaps with advancing age the eye becomes more sensitive to light!

[Gem Singer]

Harold,

If I can see the outline of my hand in a darkened room, I believe that the light is bright enough to have an effect on light sensitive materials, especially 400 speed film.

If it's not bright enough to noticeably fog film or paper, it probably will have some sort of effect on it.

For example, I know from experience that an unsafe safe light will degrade the highlights in a print.

[DanK]

I've never had a problem with Gralab timers, and have more than one mounted on the wall above the trays (16 to 18 inches.)

The older Time-O-Light timers had more illumination on the face - I always covered these when handling film.

Safelights tend to be the biggest culprits - and seem to get worse over time - a good safelight last year, sometimes isn't as great this year...

Fluorescents do have the ability to fog both film and paper, IME. I had two 2 light eight foot fixtures in my first darkroom, and had an obvious glow immediately after turning them off, and for a good bit after. I used incandescent clamp lights prior to handling film, until I replaced the flourescents.

As with anything, as long as you are aware of the potential problem you can take precautions.

A couple items often overlooked are wristwatches with the glowing faces...and cell phones... in the past, I've seen students with fogged film from both - watch on while loading film, and cell phone in shirt pocket when they get a call and it lights up...

Thanks,
Dan

[Harold_4074]

If I can see the outline of my hand in a darkened room, I believe that the light is bright enough to have an effect on light sensitive materials, especially 400 speed film.

If it's not bright enough to noticeably fog film or paper, it probably will have some sort of effect on it.

For example, I know from experience that an unsafe safe light will degrade the highlights in a print.

I agree completely (I said I was being facetious ).

Pre-exposure of film or paper to lift the very toe of the curve into the neighborhood of the fog density is a technique certainly older than I am; doing this unintentionally is certainly not good craftsmanship, even if the effect is not immediately obvious. It is one of the things which complicates "testing" of safelights by developing "unexposed" paper.

Afterglow from tubular fluorescents in a small darkroom is problematic for a reason that I don't think has been mentioned. Illumination from a point source falls off as 1/(distance squared), but that from an infinitely long "line" source only falls off as 1/(distance), and this makes a big difference. Four-foot tubes are not exactly infinitely long, but if the distance is comparable to the length of the tubes the effect will still be there. For example, on a three foot high bench under an eight foot ceiling, with end-to-end four foot lights, the illumination will definitely not obey an inverse square law.

Our more "point like" sources (small clocks, even the ring of numbers on a Gralab) are more innocuous for this reason, even if they are fairly "bright". And that tiny pinhole in the aluminum foil taped over the window, even if it is hard to look at with dark-adapted eyes, will probably not do much unless it forms an image of the outdoors on your working surface!

[Drew Wiley]

I once equipped my dkrm with high-frequency ballasts which largely eliminated the
afterglow issue, but created havoc with any hi-tech enlgr controls nearby due to EMI.
So now I just wait for the afterglow to disappear in the work areas. Over the sink itself I strictly use incandescent bulbs, and even the safelight is the old-fashioned type.

[Vlad Soare]

I'm not sure the after-glow is entirely a ballast issue. I think it has more to do with the fluorescent inner coating of the tube, which continues to emit some light even after the UV emission has ceased. Or maybe it's the mercury vapours that continue to emit some UV even after the electrical current has been interrupted? I'm not sure which one is true (possibly both? ), but I suspect that the cause of the after-glow is something of this sort, and not necessarily the ballast.
A defective or low quality ballast can probably make it worse, but I think that even with the best ballast in the world there will still be a bit of after-glow.

[Cletus]

Funny, I was curious about this and did a little test on it last night. I have a Luminox wristwatch that has pretty dang bright dial that doesn't need to be "charged" to emit it's glow - something like Tritium, but not - and I've always wondered if it would fog film.

So in total dark, I unreeled about 6" of 35mm 400ISO film and held the watch face directly against it for at least one full minute and probably two. Then, I marked that spot (snipped a little off the edge with scissors) and pulled the next 6" out of the roll. This time, I just held the watch face near the emulsion side, a few inches away and kind of moved around slowly in that orientation for about 5 minutes.

Last, another 6" and about 5 minutes, this time with the film out in the "open", but not necessarily 'aiming' the watch dial at the film. Most of the time, the watch dial on my wrist was away from the film - if you wear your watch on the inside of your wrist, YMMV on this one. This last was an attempt to somewhat simulate actual handling of the film where it might occasionally "see" the glow from the watch.

Following all that, the film was developed at 1600ISO in 1+50 Rodinal (not the best developer for this maybe) for 18 minutes.

Here's the results: First test, watch left a big, dense black spot where I had held it against the emulsion. Second test, no discernible fogging that I could see, (with caveat that I should have used film that was unexposed from the camera - I used an old roll of exposed film for this, thinking it would be good enough, but the image detail might be obscuring test results). Third test, no discernible fogging.

Conclusion: Safelight (or more powerful Luminox Watch) glow should be safe for normal ISO films as long as the exposure from the glow is kept relatively indirect to, or at least not right up against, the emulsion for short periods (<10 min.) of time while processing.

I have done a similar test with paper and can detect zero fog, even with the watch face directly against the paper (I'd never do this in practice) and I intend to rerun this test with some totally unexposed 400 film in the future with a better developer, maybe Xtol.