UV light, anyone know the actual wavelengths?

Discussion in 'Alternative Processes' started by steven_e007, Jun 9, 2009.

  1. steven_e007

    steven_e007 Member

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    Hi,

    I want to build a simple light box to have a go at some alternative processes. Living as I do in the UK natural light is a bit... unpredictable :rolleyes:

    I am starting off with simple cyanotypes and salt prints. This has been quite succesful, but I'd like a bit more consistancy and control.

    I am lucky enough to have a laser power meter which measures light intensity at various wavelengths, so I can meter up various types of UV light sources and also measure the light passed or absorbed by various diffusers, which should make life a lot easier.

    There is are obviously a lot of different sources of UV available for different purposes. The tubes used in sunbeds are quite different to the ones I use in my fishpond water purifier - and both are very different to a Disco 'Black Light' effect.

    But... can anyone tell me which wavelengths or range of wavelengths we are looking for? Sunlight obviously contains a wide mix which will change depending on latitude, time of day, condition of the sky. I have already discovered that the amount of clouds in the sky can affect contrast.

    I haven't yet found any information on sensitivity of alternative photo chemical processes that discusses specific wavelengths, though.

    Can anyone point me to any information on this? Thanks.
     
  2. Joe Lipka

    Joe Lipka Member

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  3. Steve Smith

    Steve Smith Subscriber

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    Not sure of actual wavelengths but I used to use a portable UV sun lamp for exposing screen printing emulsion.

    This is a potassium dichromate emulsion, similar to the gum bichromate process so I assume these lights would work with that.



    Steve.
     
  4. steven_e007

    steven_e007 Member

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    That's an excellent article with everything I needed to know, Thanks.

    Basically, Ed recommends 365 nm as the 'ideal' for most alternative processes such as gum, carbon, cyanotype etc, but sources that peak at 420 nm (approaching the visible blue end of the spectrum) may be better for Palladium/ Platinum, Van Dyke or kallitypes. Also, he tells us that for a given process the longer wavelengths may give more contrast.

    Fascinating!

    I can go and measure a few light sources now and see what I can come up with :D
     
  5. nworth

    nworth Subscriber

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    "Black light" bulbs peak at about 360nm. Suntan fluorescents peak at a somewhat shorter wavelength (I don't know the number). Iron based processes have a broad peak sensitivity at about 350nm, extending into the blue. The best match is the 360BL or 350BL unfiltered fluorescent lamps, but filtered fluorescent and suntan lamps will work well. Blue fluorescents will also work, with a bit less speed, but they are more expensive and harder to find than the UV bulbs. In any case, make sure you use the same type and make for all the bulbs in your exposure unit. The output of different kinds of bulbs varies a lot.
     
  6. sanking

    sanking Restricted Access

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    Thanks for the kind comments about the article. However, I am going to add that a fellow named Sandy King, not Ed, is the author of the article. Ed is a real nice fellow and gave Sandy the opportunity to place the piece on his site, but Sandy is 100% responsible for the content.

    Sandy King