Safelight question

Discussion in 'Black and White' started by Rick Helmke, Nov 27, 2017.

  1. Evening all,

    This is my 1001th post here. Only took ten years or so. Anyway as I continue to do more work in film, most of it B&W, I've run into a potential problem. Much of my darkroom gear came from a university auction as they closed down most, but not all, of their darkrooms on campus. A lot of it is equipment I used as an employee there. Among that are two Thompson duplex safelights, to me the best safelights available ever. These use, as I recall, a unique light source to create the light. It takes 10-15 minutes to warm up after it is turned on. Does anyone know what this light source is and where it might be purchased? I have other safelights as well and they would be fine but I prefer these. It may be a moot question as the lifespan on these seems nearly infinite but as soon as I get complacent they will fail or who knows, maybe they will just explode. :) Anyway are the components for these safelights available? Thanks.

    Rick H.
     
  2. It's called a low pressure sodium, or SOX, lamp. I think it's 35W. If you have never looked at yours, they're about a foot long and have a rather interesting shape.

    I have a friend in the UK who collects lightbulbs and has been after me for mine because it's the original Thomas brand one and he says private label SOX lamps are super rare.

    Unfortunately, SOX doesn't seem to have the popularity in the US as in Europe. They are available, but not overly easy to find. Expect to pay $40 or better for one.

    BTW, high pressure sodium is really easy to find(in the US). It not only uses a different fixture, but is totally unsuitable for use as a safelight. The benefit of a low pressure lamp is that it's nearly monochromatic at 589nm(a safe wavelength for paper). The filters cut out the low-intensity overtones. These are much more intense in a high pressure lamp.
     
    alan_marcus|2 likes this.
  3. Vincent Peri

    Vincent Peri Metairie, LA

    Wow, there is so much stuff I know nothing about...

    Hmm... tell me about it...
    [​IMG]
     
  4. San Jose, CA, uses low-pressure sodium for street lighting. It is easy to know when you drive over the city limit, when all the lights are yellow.

    But I suspect those are too big for darkroom use.

    I believe that there are sometimes used in physics labs, but there might not be a source for new ones.
     
  5. Glen, I think street lighting uses high-pressure sodium lamps. The band of light widens and its intensity increases with gas pressure, but it's still visually almost monochromatic.

    Low pressure sodium lamps emit mainly in the two closely spaced 'D' lines either side of 589 nanometres.

    These days, an array of amber LEDs would make a suitably narrow emission substitute. Those Duplex safelights were designed for large commercial darkrooms and are complete overkill for a small domestic setup. I believe they'll still fog modern fast varigrade paper if placed too close and for too long.

    FWIW, I think the ballast and starter for the LP sodium lamps are specialist items as well. Personally I'd use easily obtainable amber LEDs that can be run off an equally easily obtained constant-current D.C. supply.
     
  6. Correct-high pressure sodium(in street lamps) is a totally different beast.

    FWIW, my lightbulb-collector friend has told me that many of the Thomas lamps have been gutted for their fixture by bulb collectors as they are the most readily obtainable source of a SOX ballast and socket in the US.

    That same friend also tells me that the last production run of the lamps will be in 2019 or 2020, so get them while you can!
     
  7. In my day job as a chemist, I occasionally operation an atomic absorbance spectrophotometer(AAS). In a hand-waving way, light of a wavelength the same as that of the strongest emission band is put through a flame into which a sample containing the ions under consideration is aspirated. The signal is attenuated(or "absorbed") in the flame and the amount of absorbance is proportional to the same concentration.

    In any case, operation is highly element specific, and a monochromater with a small enough bandwidth to prevent interference from other elements would be both unnecessarily large and fragile. Instead, we use something called a hollow cathode lamp-it uses a small amount of the element under analysis under a low pressure inert atmosphere. Our most heavily used lamp(although we have a bunch of them) is Na/K, and of course for sodium analysis we use the narrow 589nm sodium line emitted by this.
     
  8. I just spotted a small amber LED array lamp that looked ideal as a safelight, in Google images.
    However, upon visiting the parent site I found a load of guff about 'sourced from NASA, as used by astronauts for healing purposes', and with a price tag of $199!
    Is there no end to people's gullibility, and other people's willingness to take advantage of it?

    Anyway, point is that amber LEDs with a nominal 590nm output are readily available.
     
    Last edited: Nov 30, 2017
  9. Color papers have a wavelength somewhere around the yellow where they are enough less sensitive to allow a safelight.
    (Though safedark would be more descriptive.)
     
  10. I haven't come back to this thread recently, thanks for all of this information. I also used these lights in the 70's at a couple of local newspaper darkrooms and came to like them very much. Never had a fogging problem though I always dropped the filters down and lowered the light output. $40 doesn't strike me as a bad price at all for something that seems to last for years if not decades. I think I will order a few of these and keep them as spares while they are still available.

    RIck H.
     
  11. An Osram DuKa 10 589nm wavelenght Sodium bulb, used for RA-4 color prints when you dimm the bulb mechanically with the aperture. Not suitable for B&W when you have a regular darkroom timer with sensor because Sodium lights you can not switch on-off-on. For B&W M.G. papers use an orange-red darkroom light (Kaiser - 7W or 15W max.) or selected Red LED's light with a relative small bandwith.
     
  12. I'll be ordering a few spares after Christmas but I mounted both safelights yesterday and they are exactly what I was hoping for.. Heavy as crap though. Now all I need is some new developing trays.

    Rick H.
     
  13. I have them, 30x40cm for Eur. 2.
     
  14. "Not suitable for B&W when you have a regular darkroom timer with sensor because Sodium lights you can not switch on-off-on."

    Another reason why amber LEDs would be a better option. I think the design of sodium safelights predates the invention of LEDs by some decades. Nowadays a LED safelight would be much lighter, have variable brightness and be more energy efficient, with possibly switchable wavelengths as well.

    "Now all I need is some new developing trays."

    Cat litter trays. Available in many sizes and colours, and for a fraction of the price. No grooves in the bottom, but I never found a problem with that.
     
  15. Yes, a few decades is about right. 1930 for the low-pressure sodium lamp:

    The Sodium Lamp - How it works and history

    and 1962 for the red GaAsP LED. Infrared GaAs were a little earlier.

    As well as I know, some photographic processing plants use IR light sources and IR viewers.
     
  16. 204 Euros for a car-underbody LED strip light!? Those Heiland guys are having a laugh.

    It just confirms my theory that any product with a "photographic" tag has its price inflated by anything from 2 to 10 times its real worth. They must think we're all Leica-toting spendthrifts with cash to burn.

    While on the subject of being thrifty or not. Another cheap source of developing trays is gardeners seed trays - the ones without draining holes obviously.
     
  17. I have to agree, anything that says 'photography' on it gets priced up so much higher. Same thing with aviation. I know that these safelights are good for use in a b&w darkroom as I've spent many many hours using them. Any other process I've done is always complete darkness. Cat litter trays eh? Good idea although given some of my b&w, all too fitting......

    Rick H.
     
  18. I wasn't criticising those sodium safelights for their performance Rick. I was promoting LEDs as a cheaper alternative to what could be costly maintenance if the tubes or ballast ever need replacement.

    Personally, my little Kodak "beehive" and collection of interchangable filters will do me fine. Although most of the materials the filters were designed for are out of production now!
     
  19. Rodeo Joe I think the world just moves on and leaves people like me behind. I have a few friends who think I am utterly nuts for not abandoning technology more than 15 minutes old. My wife is one....As long as I'm having fun with it she can just keep shaking her head.

    Rick H.
     

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